Government of Karnataka

SCIENCEPART-1(REvISEd)

ENGLISH MEdIUM

7SEvENTH STANdARd

KARNATAKA TEXT BOOK SOCIETY (R.)

100 Feet Ring Road, Banashankari 3rd Stage,Bengaluru - 560 085.

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Preface The Textbook Society, Karnataka, has been engaged in producing new textbooks according to the new syllabi which in turn are designed on NCF - 2005 since June 2010. Textbooks are prepared in 12 languages; seven of them serve as the media of instruction. From Standard 1 to 4 there is the EVS, mathematics and 5th to 10th there are three core subjects, namely, mathematics, science and social science.NCF - 2005 has a number of special features and they are: connecting knowledge to life activities. learning to shift from rote methods. enriching the curriculum beyond textbooks. learning experiences for the construction of knowledge. makingexaminationsflexibleandintegratingthemwithclassroom

experiences. caring concerns within the democratic policy of the country. making education relevant to the present and future needs. softening the subject boundaries integrated knowledge and

the joy of learning. the child is the constructor of knowledge. The new books are produced based on three fundamental approaches namely, Constructive approach, Spiral approach and Intergrated approach. The learner is encouraged to think, engage in activities, master skills and competencies. The materials presented in these books are integrated with values. The new books are not examination oriented in their nature. On the other hand they help the learner in the all round development of his/her personality, thus help him/her become a healthy member of a healthy society and a productive citizen of this great country, India. Mathematics is essential in the study of various subjects and in real life. NCF 2005 proposes moving away from complete calculations, construction of a framework of concepts, relate mathematics to real life experiences and cooperative learning. Many students have a maths

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phobia and in order to help them overcome this phobia, jokes, puzzles, riddles, stories and games have been included in textbooks. Each concept is intoduced through an activity or an interesting story at the primary level. The contributions of great Indian mathematicians are mentioned at appropriate places. We live in an age of Science and Technology. During the past five decades man has achieved great things and realized his dreams and reached pinnacle of glory. He has produced everything to make life comfortable. In the same way he has given himself to pleasures and reached the stage in which he seems to have forgotten basic sciences. We hope that at least a good number of young learners take to science in higher studies and become leading scientists and contribute their share to the existing stock of knowledge in order to make life prosperous. Ample opportunity has been given to learners to think, read, discuss and learn on their own with very little help from teachers. Learning is expected to be activity centered with the learners doing experiments, assignments and projects. 7th standard Social Science Textbook has been prepared based on the prescribed syllabus. And all the features of NCF 2005 and KCF 2007 have been included in the Text Book. This new Text Book has given importance to enhance the creativity of students by including activities. Many projects are included to help students to gain knowledge. This Text Book has been written in such a way that students need not memorise historical dates and other information. The Textbook Society expresses grateful thanks to the Chairpersons, Writers, Scrutinisers, Artists, Staff of DIETs and CTEs and the Members of the Editorial Board and Printers in helping the Textbook Society in producing these textbooks.

Prof. G.S. MudambadithayaChief Coordinator

Curriculum Revision and Textbook Preparation

Karnataka Textbook Society R.

Bengaluru, Karnataka

Nagendra KumarManaging Director

Karnataka Textbook Society R.

Bengaluru, Karnataka

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Chairpersons Speak

NCERT has framed National Curriculum Framework-2005 considering the educational changes at the global level. Based on this, Karnataka Curriculum Framework has been designed by involving teachers, subject experts and those who are interested in education.

Keeping in view the meaning and nature of science, the text book has been prepared on the basis of constructivism. Observation and experimentation are the basis of science. They are closely related to constructivism. An effort has been made to provide ample opportunities and encouragement to the children to draw conclusions by doing activities which promote thinking, exploringandselfexperience.Ithelpstoapplyscientificconceptsto real life experience and examples.

We hope that the box items such as Word help, Know this and Think given in each unit promote meaningful learning by involving the children in self-learning and participatory learning. We expect that the teachers and parents will help the children to develop research mind and creativity by giving co-operation and guidance to conduct the experiments and project works.

We thank all who involved in the preparation of the text book. Suggestions to improve the quality of the text book are always welcome.

dr. G.M. Nijagunadr. H.S. Ganesha Bhatta

Chairpersons

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Text Book CommitteeChairpersons:1. Dr. G.M. Nijaguna, Prinicipal(Retd.) Vijaya College, RV Road, Bengaluru.2. Dr. H.S. Ganesha Bhatta, Principal, MES College of Education,

Rajajinagar, Bengaluru.Members:1. Dr. P. Nagaraju, Vice Principal, Vijaya College, RV Road, Bengaluru.2. Sri M. Manjunathachar, H.M. GHS,Talamari, Raichur Dist. 3. Smt. Vimala Unni, # 77, Himagiri Apts., 15th Cross, Malleshwarm,

Bengaluru.4. Smt. Anuradha, Asst. teacher, Govt. PU College, Thekkatte,

Kundapura Tq., Udupi Dist.5. Smt. A.N. Shamala, Asst. teacher, Saraswathi Vidyanikethan,

Dommasandra, Anekal Tq., Bengaluru.6. Sri. L.D. Murahari, Asst. teacher, G.H.S, Kodambala, Humnabad Tq.,

Bidar Dist.7. Sri V.B. Shinge, Drawing teacher, Karnataka High School, Dharwad.Scrutinizers:1. Dr. R. Shailaja, Director, Regional Environmental Studies Center,

South Zone, 143, Infantry Road, Bengaluru.2. Sri. B.N. Suryanarayana, Principal(Retd.), KVS, West of Chord Road,

Bengaluru.Editorial Board:1. Dr.K.S. Sameera Simha, Professor(Retd.), Vijaya Teachers’ College,

Bengaluru.2. Sri B.R. Guruprasad,Scientist/PublicRelationsOfficer,ISRO,

Bengaluru.3. Dr. Katre Shakuntala, Professor of Zoology(Retd.), Bangalore University,

Bengaluru.4. Prof. V. V. Anand, Regional Institute of Education, Mysuru.Chief Co-ordinator: Prof. G.S. Mudambadithaya, Co-ordinator, Curriculum revision and

Text book preparation, KTBS, Bengaluru.Chief Advisors: Sri Nagendra Kumar, Managing Director, KTBS, Bengaluru. Smt C. Nagamani, Deputy Director, KTBS, Bengaluru.Programme Co-ordinator: Smt. N.R. Shylaja Kumari, Senior Assistant Director, KTBS, Bengaluru.

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About the Revision of TextbooksHonourable Chief Minister Sri Siddaramaiah who is also the Finance

Minister of Karnataka, in his response to the public opinion about the new textbooks from standard I to X, announced, in his 2014-15 budget speech of constituting an expert-committee, to look into the matter. He also spoke of the basic expectations there in, which the textbook experts should follow: “The textbooks should aim at inculcating social equality,moralvalues,developmentofpersonality,scientifictemper,critical acumen, secularism and the sense of national commitment”, he said.

Later, for the revision of the textbooks from class I to X, the Department of Education constituted twenty seven committees and passed an order on 24-11-2014. The committees so constituted were subject and class-wise and were in accordance with the standards prescribed. Teachers who are experts in matters of subjects and syllabi were in the committees.

There were already many complaints, and analyses about the textbooks. So, a freehand was given in the order dated 24-11-2014 to the responsible committees to examine and review text and even to prepare new text and revise if necessary. Eventually, a new order was passed on 19-9-2015 which also give freedom even to re-write the textbooks if necessary. In the same order, it was said that the completely revised textbooks could be put to force from 2017-18 instead of 2016-17.

Many self inspired individuals and institutions, listing out the wrong information and mistakes there in the text, had send them to the Education Minister and to the Textbook Society. They were rectified. Before rectification we had exchanged ideas by arrangingdebates. Discussions had taken place with Primary and Secondary Education Teachers’ Associations. Questionnaires were administered among teachers to pool up opinions. Separate meetings were held with teachers, subject inspectors and DIET Principals. Analytical opinions had been collected. To the subject experts of science, social science, mathematics and languages, textbooks were sent in advance and later meetings were held for discussions. Women associations and science related organistation were also invited for discussions. Thus, on the basis of all inputs received from various sources, the textbooks have been revised where ever necessary.

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Another important aspect has to be shared here. We constituted three expert committees. They were constituted to make suggestions after making a comparative study of the texts of science, mathematics and social science subjects of central schools (NCERT), along with state textbooks. Thus, the state text books have been enriched based on the comparative analysis and suggestions made by the experts. The state textbooks have been guarded not to go lower in standards than the textbooks of central school. Besides, these textbooks have been examined along side with the textbooks of Andhra Pradesh, Kerala, Tamil Nadu and Maharashtra states.

Anotherclarificationhastobegivenhere.Whateverwehavedonein the committees is only revision, it is not the total preparation of the textbooks. Therefore, the structure of the already prepared textbooks have in no way been affected or distorted. They have only been revised in the background of gender equality, regional representation, national integrity, equality and social harmony. While doing so, the curriculum frames of both central and state have not been transgressed. Besides, the aspirations of the constitution are incorporated carefully. Further, the reviews of the committees were once given to higher expert committees for examination and their opinions have been inculcated into the textbooks.

Finally, we express our grateful thanks to those who strived in all those 27 committees with complete dedication and also to those who served in higher committees. At the same time, we thank all the supervisingofficersoftheTextbookSocietywhosincerelyworkedhardin forming the committees and managed to see the task reach its logical completion. We thank all the members of the staff who co-operated in this venture. Our thanks are also due to the subject experts and to the associations who gave valuable suggestions.

Narasimhaiah Managing Director

Karnataka Textbook Society (R) Bengaluru.

Prof. Baraguru Ramachandrappa Chairman-in-Chief

Textbook Revision Committees Karnataka Textbook Society (R)

Bengaluru.

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Revision CommitteeChairman-in-Chief :Prof. Baraguru Ramachandrappa, State Textbook Revision Committees, Karnataka Textbook Society, Bengaluru. Chairperson : dr.S.Shishupala, Professor and Chairman, Department of microbiology, Davanagere University, Davanagere Members:Smt.K. Mamatha, Asst. teacher, GHS, Kengeri Upanagara, Bengaluru.Sri.K.S. Gireesh, Asst. teacher, GHS, Jalige, Devanahalli Tq., Bengaluru Rural Dist.Smt. G. Renuka, Asst. teacher, GHS, Honnashettihally, Gubbi Tq., Tumakuru Dist.Smt. R.N. vasantha Sujay, Asst. teacher, GHS, Hebbala, Bengaluru.Smt. A. Lakshmidevi, Asst. teacher, GHPS, Kaveripura, Bengaluru.Smt. B. Hemalatha, Asst. teacher, GLPS, K. Narayanapura, Bengaluru.Artist :Sri. U. Hazarat Ali., Lecturer, Department of Fine Arts,Tumkur University, Tumakuru.High Power Review Committee Members :dr. T.R. Anantharamu, Senior Scientist(Retd.), Geological Survey of India, Bengaluru.Prof. v.S. vatsala, Principal (Retd.), M.E.S College, Malleswaram, Bengaluru.dr. G.M. Nijaguna, Principal (Retd.), Vijaya College, Basavanagudi, Bengaluru.Prof. K.S. Nataraj, Professor of Physics(Retd.), National College, Jayanagara, Bengaluru.Translators :Sri M. Manjunathachar, H.M. GHS, Magadipalya Cross, Kunigal Tq. Tumakuru Dist.Smt. Anuradha, Asst. teacher, Govt. PU College, Thekkatte, Kundapura Tq., Udupi Dist.Smt. A.R. Shubha, Asst. teacher, G.H.S, Rajanukunte, Bengaluru.Smt. vijaya Upadhyaya, J.P Nagar, 1st phase, Bengaluru.Chief Advisors :Sri. Narasimhaiah, Managing Director, Karnataka Textbook Society, Bengaluru. Smt. C. Nagamani, Deputy Director, Karnataka Textbook Society, Bengaluru. Programme Co-ordinator :Smt. N.R. Shylaja kumari, Senior Assistant Director, KTBS, Bengaluru.

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PART-1

CONTENTS

Sl.No. UNIT PAGE NO.

1. Food and its Constituents 1 - 14

2. Cell and Cellular Organization 15 - 26

3. Friction 27 - 44

4. Acceleration 45 - 57

5. Energy 58 - 71

6.Properties of Solids, Liquids and Gases

72 - 79

7. Heat and Temperature 80 - 87

8. Acids, Bases and Salts 88 - 113

9. Atom 114 - 127

10. Hard water and Soft water 128 - 139

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UNIT - 1Food aNd ITs coNsTITUeNTs

after studying this unit you : � recognize the sources and constituents of food. � appreciate the importance of balanced diet. � explain the meaning, types and importance of carbohydrates,

proteins and lipids with examples. � cultivate healthy food habits.

Teacher : You all seem to be very cheerful and active. May I know the reason? Tell me Mohan, what is making you so happy today?

Mohan : Oh! I had my favourite breakfast -idli along with sambar and chutney.

Teacher : What did you have Razia?Razia : Chapathi and vegetable curry.Teacher : What did you have Gurmeet?Gurmeet : Bread and omelette. Teacher : What about you John?John : I had a few biscuits and milk.Teacher : Ramu, what about you?Ramu : I had a ragi ball, toor dhal sambar and

vegetable curry with rice and butter milk.In previous classes, you have learnt that we need food

for energy, growth and maintenance of our body. We obtain food from plant and animal sources. From the conversation, I learn that your breakfast includes different items. Do you think, your breakfast contains all the constituents of food and in right quantity?

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As you know, healthy food includes carbohydrates, proteins, lipids, vitamins, minerals and roughage.The food which includes the essential nutrients in a definite quantity is termed as balanced diet.

Fig. 1.1 : Sources of balanced diet

Know this :Water is essential for every organism on earth. Sufficient quantity of water is required by our body cells for their proper functioning. Our body metabolism also depends on water. Water helps our body to absorb nutrients and to discharge wastes.

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Here is an analysis of Ramu’s breakfast. It includes,ragiball - contains carbohydrates and

roughage.sambar and vegetable curry - contain proteins, lipids, vitamins,

minerals and roughage.rice - contains carbohydrates.butter milk - contains all components of milk

with almost no fats.What is your conclusion? Is Ramu’s breakfast a balanced

diet?Is it possible to obtain all the nutrients from a single food

item?

Activity 1.1 : With the help of your teacher, prepare a chart of various sources of food and the nutrients in them.

Activity 1.2 : Make a list of breakfast items of your friends. Tick the nutrients present in them in the table given below.

Name Breakfast items

Carbo-hydrates Proteins Lipids Vitamins Minerals Roughage

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Whose food is balanced? Why?

In this unit, you learn more about carbohydrates, proteins and lipids.1. carbohydrates :

Carbohydrates are commonly called sugars or saccharides. They are made up of carbon, hydrogen and oxygen.

Observe the structure of a carbohydrate molecule shown in the figure. Red balls represent carbon atoms, black balls oxygen and green balls represent hydrogen. The tubes shown here bind all these together. Major portion of energy released in our body is from carbohydrates.

Types of carbohydrates :

There are three types of carbohydrates. They are monosaccharides, oligosaccharides and polysaccharides.

Do you know why the patients and athletes are given glucose?

Glucose is a simple sugar unit (molecule). What do fruits contain? They contain another simple sugar called fructose. Glucose and fructose are called monosaccharides. Another type of sugar called galactose also belongs to this group . All these contain six carbon atoms. Hence, they are called hexose sugars. Sugar with five carbon atoms are called pentoses. Ribose and deoxyribose are pentoses. Thus, monosaccharides are carbohydrates containing one simple sugar molecule. They are sweet to taste and soluble in water.

Fig. 1.2 : Structure of a carbohydrate molecule

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Know this :Glucose, fructose glucose fructose galactose

C6H12O6C6H12O6 C6H12O6

Fig. 1.3 : Structure of simple sugars

and galactose have same general molecular formula and differ only in the structure, arrangement of the various atoms with in the molecule.

Do you drink milk every day? Have you tasted milk without sugar? Is it sweet? Do you know that milk contains a sugar called lactose. The sugar that you add to milk is sucrose or common sugar. Both lactose and sucrose are the examples of disaccharides. Even maltose present in cereals is a disaccharide. A disaccharide is made of two units of monosaccharides. Disaccharides are also sweet to taste and soluble in water.

Lactose (milk sugar) = Glucose + Galactose

Sucrose (cane sugar or = Glucose + Fructose table sugar)

Maltose (malt sugar) = Glucose + Glucose

oligosaccharides may be formed by the linkage of two to ten monosaccharide units. Linkage between two adjacent monosaccharides is called glycosidic bond.

A plant cell has a cell membrane and a cell wall. Usually the cell wall is made up of cellulose. cellulose is formed of many (more than 10) monosaccharide units. Hence, it is called a polysaccharide. Another example of a polysaccharide is starch. Starch is the reserve carbohydrate in plants.

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Starch is tasteless and insoluble in water. It breaks up into glucose molecules in the process of degestion which are absorbed by the blood in our body.

Glycogen is another polysaccharide which is found in animals including human beings. Glycogen is described as animal starch.

When there is excess of glucose in our body, a part of it is converted into glycogen. It is usually stored in the liver and muscles, especially skeletal muscles. Extra glucose is also converted into fat. Both glycogen and fat provide us energy during starvation.

Know this :Human liver stores about 100 g of glucose as glycogen while skeletal muscles store about 400 g of glucose as glycogen.

Importance of carbohydrates :

1. Glucose is the principal source of energy for all our activities.

2. Deoxyribose, a pentose sugar is a part of our genetic (hereditary) material.

3. Starch and glycogen serve as energy storage products.

4. Polysaccharides like cellulose, hemicellulose, lignin and pectin though do not supply energy, are important as fibrous components (roughage) of our food.

Think :

We cannot digest cellulose and other fibrous materials. Why?

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2. Proteins :

Proteins are made up Know this :

Fig.1.4 : Structure of a generalised amino acid

molecule

Group Carbon

Carboxyl groupAmino group

of amino acids. Amino acids contain carbon, hydrogen, oxygen and nitrogen. There are 20 different types of amino acids. These amino acids are linked by peptide bonds to form proteins (polypeptides).

Know this :Amino acids can be grouped as essential amino acids and non-essential amino acids.i) Essential amino acids : These are not synthesized in our body but are required for the growth and function of our body. Hence they have to be taken as a part of the diet. Essential amino acids are present in soyabean, pulses, meat, milk etc. For example, lysine and valine. Among the twenty types of amino acids, only nine are essential. Such amino acids can be obtained by different sources of food.ii) Non-essential amino acids :These are synthesized in our body. Hence, they need not be a part of our diet. For example: proline and serine.

Types of proteins :We consume pulses or dhals and milk regularly. Do you

know why? They contain proteins. Even egg and meat are rich in proteins. Egg white contains proteins (albumins) that are made up of only amino acids. Such proteins are called simple proteins.

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You know that our blood is red in colour. Can you name the substance that gives red colour to our blood? It is haemoglobin. Haemoglobin is made up of a simple protein called globin and a non-protein part called haem. Such proteins which are made up of a protein and a non-protein component are called conjugated proteins.

Activity 1.3 : Contact a diagnostic laboratory or hospital and obtain the haemoglobin values of at least 20-25 persons. Compare the values and find out how many of them have normal haemoglobin level and how many have less than the normal amount? What conclusions do you draw?Importance of proteins :

1. Proteins are present in the cell membrane, hair, nails, bones, cartilage, tendons and muscles.

2. They regulate various life processes.3. They increase the rate of chemical reactions in

our body.4. They cause the muscle contraction and help in our

movement.5. They help in transporting substances. For example,

haemoglobin transports oxygen.6. They provide immunity to the body.7. They help in blood clotting and prevent bleeding.8. They are essential for the growth of our body parts.

3. Lipids :Like carbohydrates, lipids are also made up of carbon,

hydrogen and oxygen. But, they contain less oxygen than in carbohydrates. A lipid molecule is made up of building blocks called fatty acids linked by ester bonds. Lipids are insoluble in water. But are soluble in organic solvents like ether.

Are you fond of butter, ghee and cheese? What are they? They are animal fats. Similarly, we consume vegetable oils like groundnut oil, mustard oil, sesame oil and coconut oil.

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Fats and oils made up of fatty acids and glycerol are simple lipids. Fats are solids and oils are liquids at room temperature.

When lipids combine with other groups like glucose and protein etc., they form compound lipids.

Lipoprotein is an example of compound lipids.Importance of lipids :

1. Along with carbohydrates, lipids (fats) also provide energy.

2. Fats act as thermal insulators and help in maintaining body temperature.

3. Lipids are a part of cell membrane.Know this :

Fatty acids may be saturated with no double bonds in the molecule or unsaturated with one or more double bonds. Vegetable oils like sunflower oil, soyabean oil are unsaturated while animal fat and vegetable oils like coconut oil, palm oil etc., are saturated. Saturated fats are dangerous as they lead to narrowing of blood vessels which in turn leads to high blood pressure, heart attack etc.

3. Necessity of fibre in food :Suresh was suffering from stomach pain. When teacher

asked, he told that he felt difficult to pass stool that day. This is called constipation. You might have heard that doctors usually suggest eating banana at the time of constipation. It is very important to have enough fibre in our food. Fibre prevents hardening of stool, after digestion of the food. Green vegetables, fruits, and millets like ragi, pearl millet, foxtail millet, kodo millet etc., are rich in fibre. They help in proper digestion of food and prevents constipation.Activity 1.4 : List out the food items which contain fibre. With the help of the teacher know the percentage of fibre in these food items.

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Know this :Food items and their energy value in kilo calories (Kcal) against quantity (Reference: Dietary guidelines for Indians, National Institute of Nutrition, ICMR, Hyderabad, 1998).

Food Items Quantity per serving Energy in KcalRice 1 cup 170Bread 2 slices 170Upma 1 cup 270Idli 2 No. 150Dosa 1 No. 125Poori 1 No. 100Cereal flakes with milk 1 cup 220Boiled Dhal ½ cup 100Boiled egg 1 90Fish (fried) 2 big pieces 220Omelette 1 160Vada 2 No. 140Cheese balls 2 No. 250Ice cream ½ cup 200Tea/Coffee 1 cup 100Milk 100 g 70Cashew nuts 10 No. 95Peanuts 50 No. 90Apple 1 medium 65Banana 1 medium 90Guava 1 medium 50Grapes 30 No. 70Jack fruit 4 pieces 90Mango 1 medium 180Moosambi/Orange 1 medium 40Papaya 1 piece 80Water Melon 1 slice 15Sapota 1 medium 80Soya bean 100g 432Peas 100g 315Bengal gram 100g 360

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Word help :

Calorie - quantity of heat required to raise the temperature of 1g of a substance to 10 C.

1 Calorie = 4.2 joules

Know this :Malnutrition: The term malnutrition refers to a condition which occurs due to an absolute deficiency or excess of one or more essential nutrients. It includes under nutrition, over nutrition, imbalance and specific deficiency.

Remember

� We need food for energy, growth and maintenance of our body.

� Food is obtained from plant and animal sources.

� A balanced diet includes carbohydrates, proteins, lipids, vitamins, minerals and roughage.

� Carbohydrates are made up of carbon, hydrogen and oxygen.

� The three types of carbohydrates are monosaccharides, oligosaccharides and polysaccharides.

� Proteins are made up of amino acids.

� The two types of proteins are simple proteins and conjugated proteins.

� Lipids are made up of carbon, hydrogen and oxygen. But they contain less oxygen than in carbohydrates.

� The two types of lipids are simple lipids and compound lipids.

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Tips

y Have a balanced diet for a healthy body. y Avoid junk food, select your food wisely.

y Drink atleast 2 litres of clean water per day.

exercises

I. Four alternatives are given under each complete/ incomplete statement. choose the correct answer and put a tick () mark against it :

1. One of the following is an energy source for our body.

a) carbohydrates b) minerals

c) vitamins d) roughage

2. The number of molecules of simple sugars in an oligosaccharide isa) three b) two to ten

c) more than ten d) two

3. The principal energy source in our body is a) glucose b) maltose

c) starch d) glycogen

4. The constituents of food which serve as thermal insulators are

a) carbohydrates b) proteins

c) fats d) roughage

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II. Fill in the blanks with suitable words :

1. A simple lipid which is solid at room temperature is ___________.

2. An example of conjugated protein is___________.

3. In carbohydrates, hydrogen and oxygen are present in a ratio of _____________.

4. Proteins are made up of ______________ .

5. An example of animal carbohydrate is___________.

III. Match the following :

a B1. fructose a) roughage

2. glycosidic bond b) simple lipid 3. cellulose c) simple proteins

4. proteins made up of d) linkage between two only amino acids monosaccharides5. vegetable oil e) monosaccharide

f) oligosaccharide

IV. answer the following questions :

1. Name any three constituents of our food.

2. Which two constituents of food provide energy for our body?

3. What are carbohydrates? Give two examples.

4. Write a difference between monosaccharides and oligosaccharides. Give an example for each.

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5. Mention the importance of the following.

a) carbohydrates b) proteins c) lipids

6. Name the storage carbohydrate in plants and the storage carbohydrate in animals.

7. Differentiate an amino acid from a protein.

8. What are proteins? Give two examples.

9. Define simple proteins. Give an example.

10. What do you mean by a conjugated protein? Give an example.

11. What are lipids? Give two examples.

12. Write a difference between fat and oil. Give an example for each.

13. What are simple lipids? Give an example.

Project Work

� Collect information about the causes, effects and remedies of malnutrition.

� Organise a poster exhibition in your school to create awareness about the importance of balanced diet. Highlight the effects of malnutrition and under nutrition.

� Take up a survey of a community to know about the food habits of its residents. With the help of your teacher, prepare specific questions and seek answers from the people included for the survey. Analyze the data and draw conclusions regarding their nutritional status and health.

RR

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UNIT - 2cell aNd cellUlaR ORGaNIZaTION

after studying this unit you : � understand and describe the structure of a cell. � distinguish between prokaryotes and eukaryotes. � differentiate unicellular and multicellular organisms. � develop the skill of drawing the diagram of a cell and

labelling its parts. � appreciate different levels of organization of organisms.

In your previous classes, you have come to know that on our planet earth, there are numerous varieties of plants and animals living in different habitats. In addition to them, there are also a variety of organisms like viruses, bacteria, lower forms of plants and animals. These organisms are not visible to the naked eye but are visible under a microscope. Hence, such organisms are called micro-organisms.

Know this :anton van leeuwen hoek, a Dutch optician, observed that tiny objects appear big when viewed through the lenses. Using the lenses, he designed an instrument through which he could see objects, ordinarily not visible to the naked eye. With the help of this microscope he studied micro organisms.

Activity 2.1 : Make a list of different types of microscopes.

What is the body of these organisms made up of ?You already know that every organism is made up of tiny

units called cells. Who discovered the cells?

Fig 2.1: Leeuwen hoek observing throgh the Microscope designed by himself.

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Robert Hooke, an English scientist discovered the cells. When he viewed a thin slice of cork through a microscope, he was amazed to see tiny compartments closely arranged like a honeycomb. He named these tiny structures as cells.

Know this :Parashara, an ancient Indian sage, lived around first century AD. He has written a book called Vrikshayurveda. In this book, he has described various aspects of plants and agriculture. According to him, a leaf (parna) contains a number of tiny structures not visible to the human eye. He named them rasakoshas (now called cells). He even says that these rasakoshas contain a pigment (varnike) which helps in preparing food.

What is a cell made up of ?A cell is made up of a colourless jelly-like substance

called protoplasm It is enclosed by a membrane called the cell membrane or plasma membrane. Each cell contains a nucleus and cytoplasm. Protoplasm inside the nucleus is nucleoplasm which is surrounded by a nuclear membrane.The Protoplasm present between the nucleus and the plasma membrane is known as cytoplasm. Inside the cytoplasm, there are several tiny structures called cell organelles.

Word help :

Organelle - Living component in a cell with specific structure and function.

Are the cells of all organisms similar?Yes. The basic structure of cells of different organisms is

similar. A cell is described as the basic structural and functional unit of an organism. Like bricks forming structural units of a house, cells are the structural units of the body of an organism. Cells are of various shapes and sizes.

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Know this : � The largest cell is ostrich egg which is about 15 cm long,

13 cm wide and nearly 2 kg in weight. � The longest animal cell is nerve cell which measures

about 90 cm in length. � The longest plant cell is sclerenchyma fibre from Hemp

plant and it measures about 100 cm in length. � The smallest cell is the bacterial cell, mycoplasma which

measures 0.1 micro metre(µm) to 0.25 micro metre (µm) in size.

Now, let us understand the cellular organization in organisms.

In organisms, there are two basic types of cells based on their structure. They are prokaryotic and eukaryotic cells.

In lower organisms, the body is made up of a simple cell . In this cell, the nucleus is not surrounded by a nuclear membrane. Such a nucleus is called a primitive nucleus. Usually its genetic material is represented by naked Deoxy Ribo Nucleic Acid (DNA). The cell is surrounded by a cell membrane and a cell wall. The cytoplasm shows small ribosomes but organelles like mitochondria, endoplasmic reticulum and golgi complex (see figure 2.2) are absent. A cell with this pattern of structure is called a prokaryotic cell and the organism that possesses this type of a cell is called a prokaryote. Prokaryotic cells are seen in bacteria, cyanobacteria and mycoplasmas.

Fig. 2.2 : Structure of a prokaryotic cell

DNA

cell membrane

ribosome

cell wall

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Word help :

The word prokaryote is derived from two Greek words: Pro and karyon Pro means first or primitive and karyon means nucleus.

In majority of organisms, the cell has a nucleus surrounded by a nuclear membrane. Inside the nucleus, the genetic material is present in the form of chromatin. Such a nucleus is called a true nucleus. Cytoplasm shows large ribosomes and organelles like mitochondria, endoplasmic reticulum and golgi complex. A cell with this pattern of structure is called a eukaryotic cell and the organism that possesses this type of cell is called a eukaryote. All organisms other than bacteria are examples of eukaryotes.

Word help :

The word eukaryote is derived from two Greek words: Eu and Karyon. eu means true and karyon means nucleus.

cell membrane

nuclear membranenucleolus

nucleoplasm

ribosomemitochondrionlysosome

golgi complexcentriole

chromatin endoplasmic reticulumribosome

cytoplasmvacuole

Fig. 2.3 Structure of a eukaryotic cell

nu

cleu

s

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different parts of a eukaryotic cell and their functions :

Parts of a cell Functions

Nucleus

Controls and co-ordinates all the activities of the cell. Hence, it is called the headquarter of the cell.

MitochondrionHelps in producing energy from food. Hence, it is called the power house of the cell.

Ribosome Helps in protein synthesis. Hence, it is called protein factory of the cell.

Centriole Helps in cell division.

VacuoleStores wastes, secretions and reserve food products produced in the cells.

Endoplasmic reticulum

It transports substances from one part of the cell to the other and from one cell to another.

Golgi complexIt helps in the secretion of chemicals required for cellular activities.

Lysosome

Helps in the digestion of organic substances present in the cell. It destroys its own cell when cell becomes old or damaged. Hence, it is also called suicide bag of the cell.

Fig. 2.4: Eukaryotic cell - Parts and their functions

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Know this :In plants with eukaryotic cells, another type of organelles called plastids are present. Among the different types of plastids, the green coloured chloroplasts are most common and these help in photosynthesis.

differences between prokaryotic and eukaryotic cells :

Sl.No. Feature Prokaryotic cell eukaryotic cell

1. Nature of nucleus

Primitive or incipient, without

a nuclear membrane

True nucleus with a definite

nuclear membrane

2. Genetic material

Represented by naked DNA

Organized into definite

chromosomes3. Cell organelles

like mitochondria, golgi complex, endoplasmic

reticulum

Absent Present

4. Ribosomes Small Large

Activity 2.2 : Demonstration of cells in the onion peel.(by the teacher)

Take a clean glass slide with a drop of water on it. Remove a small piece of onion peel and place it on the water drop. Put a small drop of eosin or saffranin stain on the peel. Now place a cover glass on the peel and examine under a compound microscope. Identify the cell wall, cytoplasm and nucleus in the cells.

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Organisms may be made up of a single cell or many cells. If the body of organisms consists of only one cell, then such organisms are called unicellular organisms. In such organisms, the single cell feeds, grows, respires, excretes, responds to stimuli and reproduces like any higher or complex organism. Within the cell, there are various structures specialised for carrying out specific functions. Unicellular organisms include Bacteria, certain Algae such as Chlorella, Protozoans such as Amoeba, Euglena, Paramecium, etc.

Amoeba Euglena Paramecium

Fig. 2.5 : Unicellular organisms

There are organisms whose body is made up of many cells. Such organisms are called multicellular organisms. They can be either Hydra like micro scopic organism or large in size.

AntHydra Elephant Banyan tree

Fig. 2.6 : Multicellular organisms

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Usually in multicellular organisms, the cells are differentiated to perform specific functions. There are multicellular organisms in which cells are not differentiated into tissues. They show cellular grade of body construction but in most of the multicellular organisms, we observe that cells differentiate into true tissues and organs for specific functions. Thus they show tissue level, organs-system level of body organization.

Let us consider Human as an example and study the various levels of body organization.

Organism Many systems work together in our body to carry out the life processes.

OrganSystem

It is a combination of different organs which work together to carry out a particular function.

Organ It is a combination of different types of tissues which performs a specific function.

Tissue A tissue is a group of cells with similar structure and function.

Cell It is a tiny basic unit of an organism.

What conclusion do we draw from the above information?

Fig. 2.7 : Levels of organization in the human body

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We realize that in multicellular organisms with tissues, organs and organ-systems, there is division of labour.

Activity 2.3 : Prepare a list of various tissues and organs of a flowering plant and also prepare a list of various tissues, organs and organ systems in humans. Know each of their functions from your teacher and appreciate the concept of division of labour.

Flowering plant Human

Tissues Organs Tissues Organs Organ systems

Remember � Leeuwenhoek invented the micro organisms. � Robert Hooke discovered the cell. � Cell is the basic unit of an organism. � Organisms which possess simple cells with primitive

nucleus are called prokaryotes. � Organisms which possess complex cells with true nucleus

are called eukaryotes. � There are different levels of organization among organisms

such as cell, tissue, organ and organ system levels. � Tissue is a group of cells with similar structure and

function.

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� Organ is a combination of different types of tissues which performs a specific function.

� Organisms with a single cell are called unicellular organisms.

� Organisms with many cells are called multicellular organisms.

Tips

y Every organism, simple or complex has a right to live on the earth. Therefore, live and let live.

eXeRcISeS

I. Four alternatives are given under each complete/ incomplete statement. choose the correct answer and put a tick () mark against it :

1. Micro organisms are invented by a) Leeuwenhoek b) Parashara

c) Robert Hooke d) Robert Brown

2. Cell is discovered bya) Leeuwenhoek b) Robert Brown

c) Robert Hooke d) Parashara

3. A true nucleus is present in a) prokaryotic cell b) bacterial cell c) virus d) eukaryotic cell

4. The power house of a cell isa) nucleus b) ribosome

c) mitochondrion d) lysosome

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5. A group of cells with similar structure and function is a

a) tissue b) organ

c) organ system d) organism

II. Fill in the blanks with suitable words :1. The combination of different organs which carry out a

particular function is called ____________ .2. Ribosome helps in ____________ .

3. Lysosome helps in the digestion of ____________ .

4. Paramecium is an example for ____________ organisms.

5. The part which controls and co-ordinates all the activities of the cell is ____________ .

6. In a prokaryote, genetic material is represented by ____________.

III. answer the following questions :1. Define a cell. Explain the structure of a typical cell.

2. Draw a neat diagram of a eukaryotic cell and label its parts.

3. Differentiate between an organ and a tissue.

4. Mention the functions of the parts of a eukaryotic cell.

5. Distinguish between the following pairs-

a) prokaryotic and eukaryotic cells.

b) unicellular and multicellular organisms.

6. Draw a neat labelled diagram of a prokaryotic cell.

7. Describe the structure of a eukaryotic cell.

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8. Name the four levels of body organization in organisms.

9. Mention the advantage of tissue-organ level of body organization.

Project work

� With the help of your teacher, study the various parts of simple and compound microscopes present in your school. Classify the parts into optical and mechanical parts. Calculate the magnification power of each type of microscope. Which of the microscopes is advantageous and why? Make sketches and label the parts.

Use this :1.Magnification power of simple microscope = magnification power of eye lens2. Magnification power of compound light microscope = magnification power of

eye lens X magnification power of objective lens.

� Collect a water sample from a nearby pond or tank in the presence of your teacher. Place a drop of this sample on a glass slide and observe under a compound microscope. Look out for the presence of living organisms. If possible, identify them with the help of your teacher.

� Collect a water sample from a pond or tank in the presence of your teacher. Boil tap water mixed with dry grass taken in a large beaker. Cool this and mix it with the water sample (from pond) taken in a glass trough or large beaker. Leave it for a few days. Then, take drops of this sample on a glass slide and observe under the microscope. Observe the presence of Amoeba, Paramecium and such other organisms.

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UNIT - 3FRICTION

After studying this unit you :

� give illustrations of friction in day-to-day life.

� explain the cause for friction.

� define the term friction and its types.

� measure the frictional force.

� make a list of various factors affecting the friction.

� compare the magnitudes of different types of friction.

� classify the effects of friction.

� reason out the need for friction.

� distinguish between advantages and disadvantages of friction.

� differentiate the methods of increasing and decreasing the friction.

You might have seen that a moving ball slows down and stops after travelling some distance. Why is the sharp tip of a pencil become blunt while writing? why your bicycle slows down when brakes are applied? When you strike a matchstick against the smooth surface of an old match box it will not light up. Why? Why is it difficult to write on a smooth and slippery black board?

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Fig. 3.1

A body sliding over the surface of the other slows down. We know that force make the bodies to move or stop the moving bodies. Friction is such a force which tends to slow down or stop the moving bodies. Frictional force always acts in the direction opposite to motion.

A moving ball slows down because of the friction between the surfaces of the ball and the ground. Pencil becomes blunt because of friction between its tip and the surface of the paper. Friction between the brakes and the wheel stops the vehicle. Match stick do not light up due to lack of friction with the worn match box. Similarly writing won’t be clear on smooth black board because of least friction.

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Frictional force :Activity 3.1 : Try sliding

Fig. 3.2

a wooden block kept on a rough flat table as shown in the figure. Push the block with a small horizontal force, it does not move. Can you say that there is another horizontal force opposing the applied force? Yes, this opposing force is known as the frictional force, which is excerted by the table on the wooden block. When the applied force is gradually increased the block starts moving. Now actually the applied force exceeds the maximum frictional force.

A force that always opposes the relative motion of two surfaces in contact with one another is called frictional force.

How is Friction Caused?

A frictionless surface is only an imagination. All surfaces experience friction as they rub across each other. How ever smooth any two surfaces may be, on observing through a microscope you will see the irregularities on their surfaces. So when two bodies are placed upon one another the irregularities of the surfaces interlock.

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Think :Is there any place where there is absolutely no friction?

When a force is applied on a body sliding over another, its interlocked irregularities collide each other. Mutual forces between them opposes their sliding.

Measuring Frictional force :

Frictional force can be measured by a spring balance.

Activity 3.2 : Keep a stone on a table and tie a thread around it. Pull the stone using a spring balance as shown in the figure. Observe that the stone initially does not move. However when the applied force is gradually increased for a moment it just begins to slide. Note down reading on the spring balance. This gives the force of friction which opposes the applied force.

Fig. 3.3 : Pulling a stone using spring balance

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Factors affecting friction :

Activity 3.3 : Take an empty box, tie a string around it and pull the box slowly on a smooth surface of a floor. Do you feel any friction? Try pulling the same box on the different surfaces over the floor, such as a thick sheet of cloth, a sheet of coir mat, a sheet of rubber, a sheet of greasy paper and finally on a sand bed. What change do you observe in the magnitude of friction ? Repeat the same activity using a heavily filled box. Observe the difference. What might be the reason for this difference?

A boy pulling a box on a sand bed

A camel walking on a desert feels friction

Fig. 3.4

y Frictional force is caused due to inter molecular interactions between the bodies.

y Frictional force always opposes relative motion. y Frictional force vary in strength according to how hard

the two surfaces are pressed against one another and how slippery or how rough the surfaces are.

y The harder you press the two surfaces together, larger the frictional force they experience.

y Frictional force is more for rough surfaces and less for smooth surfaces.

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Types of Friction :Let us compare the friction between the surfaces of two

stationary bodies, to the surfaces of two sliding and rolling bodies.1. Static friction :

Activity 3.4 : Try to slide a heavy box

Fig. 3.5 : A person pushing a big heavy

box on the floor.

over the floor, A Small push does nothing. You find it particularly hard in the beginning because, the contact points of irregularities between the box and the floor have settled inter- locking one another. This opposition is due to friction which prevents two surfaces to slide across one another.

The force of friction acting between the two bodies does not allow them to start slide upon one another is called static friction.

Think :Why do automobiles require a push by heavy (first)

gear in the beginning of their movement?

2. Sliding friction : (Continuation of the previous activity 3.4)

Activity 3.5 : To get the box moving, more force is required to overcome static friction between the surfaces. Now push with more horizontal force than the static friction can excert. Once the box is moving static friction is replaced by another frictional force, which acts to stop the surfaces from sliding.

The force of friction acting between the two bodies when they are sliding upon one another with a uniform speed is called sliding friction.

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It is easier to keep the box moving than to get it started, therefore sliding friction is generally less than the static friction.

3. Rolling friction :

Have you ever felt rolling a pencil

Fig. 3.6 Rolling a pencil

between the palms

between your palms is easier than rubbing without a pencil? Try this.

In the previous activity 3.5, could it be easy to push the heavy box over roller wheels? Think.

Rolling bodies are not free from friction. When the surface of one body rolls over the surface of the other, the force of opposition offered to its motion is called rolling friction.

Actually rolling reduces friction. It is always easier to roll than to slide a body over another. Hence rolling friction is less than the sliding friction. Ball bearings works on this principle.

Know this :Static friction > Sliding Friction > Rolling Friction.

Effects of Friction :1. Friction Opposes motion :

When force is applied on a body to move over the other body, the irregularities of the surfaces interlock. Frictional force created due to this cause always acts in the opposite direction of the applied force. Therefore Friction always opposes the motion of the body and tries to stop it

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Example: Bicycle braking system works on the basis of this effect of friction.

Fig. 3.7 : Bicycle brake system2. Friction produces heat :Activity 3.6 : Take an iron nail, rub it on a rough stone surface. What do you observe? The nail becomes hot because of the friction. It is for the same reason that your palms get warm when rubbed against each other. The jar of the mixer grinder gets hot when run for a few minutes. In fact all moving parts of the machines get hot because of friction.

Hand pumpMixer grinder with a jar

Fig. 3.8

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Know this :In ancient times fire was produced by rubbing fire stones.

Think :Why do meteors catch fire and burn completely before

reaching the earth?

3. Friction causes wear and tear :

Have you ever compared the sole of an old shoe with that of new one? The soles of old shoes are worn out. Do you know why? It is because, when we walk or run, the sole material gets worn out due to friction with the floor.

Similarly the tyres of the vehicles, rubber bushes of furniture wear out due to friction. Moving parts of the machine under friction are frequently replaced due to wear and tear.

Fig 3.9: Worn out tyres and shoes

Friction - A necessary evil :

Friction plays a very important role in many of our life situations. So friction necessarily provide some advantages.

Just think, Is it easier to catch a slippery fish in your hand? Would it be simply possible to hold a wrestler who has applied oil on his body? No, we can not hold any thing without friction. Wall holds a screw or a nail only because of friction.

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H a v e y o u s e e n

Fig. 3.10 : Buffalo race on a muddy track (Kambala)

the buffalo race on a slushy track (Kambala)? Could it become more difficult or easier to ride your bicycle on a wet muddy track? However if there is no friction, the bodies will either slip or will not move. Further more the moving bodies will not stop. Even we can not walk properly without friction. It is very difficult to walk on smooth and wet floor as friction is very less. While we walk, friction between the ground and the feet prevents us from slipping.

Think :Why does the wheel of a vehicle caught in a slushy

ditch simply rotates there as it tends to move forward?

Do you know, we can not even write on anything without friction, and even no knot could be tied without friction Example, Match stick catches fire because of heat produced by the friction. Without friction the pulley of a motor can not move the conveyor belt to run a machine.

Fig. 3.11: A conveyor belt pulling a wheel

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However in some other cases friction is an evil, and it creates some disadvantages.

Force of friction brings about wear and tear in moving bodies. You might have seen worn out tyres of the automobiles, worn out soles of the shoes, worn out mechanical parts and ball bearings of the machines due to friction. Friction reduces the speed of the machines. The movable parts of a machine produce huge amount of heat, it leads to much loss of energy. Therefore the energy required to operate the machine increases by friction and friction reduces efficiency considerably.

So friction is both useful and harmful at different situations and hence it is a necessary evil.

Methods of increasing friction :Even though friction is an evil, it is necessarily required at

a desired level for the better grip in our day-to-day activities. In order to increase friction generally the surfaces in contact are made rough.

Have you observed spikes provided in the shoes of athletes, cricket players and rock climbers? Spikes increase friction and provide desired grip in their movement.

You might have seen automobile handles, steerings, foot rests, the handles of sports bats, suit cases, walkers and ramps. They are generally covered by holding grips of grooved rubber, They provide required friction in handling them.

Usually rubber bushes are fixed at the bottom of ladders, walking sticks and furniture to avoid slipping.

Have you seen the flooring of toilets, bath rooms, step edges of staircases? They have rough surfaces to provide grip while walking on them.

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Worn out tyres of the vehicles

Fig. 3.12 New tyre with heavy

treads and groves

may skid on the sharp turns of the roads due to less friction, and can cause serious accidents. It is for the same reason that special kinds of treads and groves are made in new tyres.

Braking system of the vehicles are provided with rough surfaces to acquire required friction, Grinding stones of the flour mills are designed with rough groves to increase friction in grinding.

Do you know why kabaddi players and wrestlers rub their hands with soil ? Weight lifters, gymnants use some coarse meterial ? It is to increase friction for better grip.

Kabaddi players WrestlersFig. 3.13

Increase in friction saves the energy in the above situations.Methods of reducing friction :

We know that friction is basically created due to inter locking irregularities of two surfaces.

In certain situations however friction is undesirable must be reduced so as to increase efficiency. In order to reduce friction generally the surfaces in contact are made smooth and slippery.

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Have you played carrom?

Fig. 3.14 Playing carrom

A fine talcum powder is sprinkled on the carrom board. Do you know why? It is to reduce friction between the board and the striker, so that the striker and coins’ movement become easier.

Think :Why are gel pens used for

faster hand writing?

You might have felt very comfort able to peddle your bicycle, when its chain and hubs are properly oiled. Similarly when a few drops of oil are poured on the hinges of a door, the door moves smoothly. Here oil acts as a lubricant to reduce friction.

A lubricant is a substance which reduces friction between surfaces in contact.

Oil, grease, graphite and soap solutions are commonly used as lubricants in machines. A thin layer of lubricant separates the two moving surfaces, so that they do not rub against each other directly.

Activity 3.7 : Take a sheet of paper. Hold it horizontaly and allow it to fall down. Observe the time taken to fall. Now crumple the same paper into shape of a ball and again allow it to fall down. You notice that the crumpled paper ball reaches the ground quicker than the spreaded sheet. Do you know why?

Fig. 3.15 Lubricating the bicycle

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Air and fluids like water

Fig 3.16

Submarine’s stream-lined shape

offer friction to the bodies moving through them. Modern automobiles, aircrafts, boats ships and submarines are given a streamlined shape so that they offer least friction to the air or water.

Think :Why have fishes and birds stream lined shape?

It is strainless to move on scating rollers, than to walk or run. Do you know why? We know that the wheel is one of the greatest inventions of the mankind. Wheels can easily roll and hence they reduce sliding friction. Rolling friction is generally less than sliding friction.

It is for the same reason, many heavy objects and luggages are fitted with small wheels called rollers.

Ball bearings used to run heavy machines and wheels of the automobiles reduces the friction to a large extent.

Pulling a luggage bag with rollers

ball bearings

Fig 3.17

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Remember

� Friction is a force which tends to slow down or stop the moving bodies.

� Friction opposes the relative motion between the two surfaces in contact.

� Friction is caused due to interlocked irregularities of the surfaces in contact.

� Friction depends on how hard the two surfaces pressed together, and how rough they are.

� Without friction no bodies will move, and even moving bodies will not stop.

� Static friction does not allow the surfaces in contact to start slide upon one another when they are at rest.

� Sliding friction does not allow the surfaces in contact to slide with uniform speed.

� Rolling friction does not allow the surfaces in contact to roll over another.

� Things moving under friction produce heat, noise, wear and tear resulting in loss of energy.

� Friction can be reduced by using lubricants, polishing surfaces, stream- lining and by using ball bearings.

Tips

y Apply oil or grease on the movable parts of the machines to reduce friction.

y Carry heavy things on rollers with ball bearings to save energy and to reduce friction.

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y Do not use highly polished flooring tiles in toilets and bathrooms.

y Replace worn out tyres of the vehicles to avoid accidents due to skid.

y Use foot wears and seat belts with proper grip to gain necessary friction.

Exercises

I. Four alternatives are given under each complete/ incomplete statement. Choose the correct answer and put a tick () mark against it :

1. Friction is caused mainly due to

a) softness of the surfaces

b) hardness of the surfaces

c) irregularities of the surfaces

d) smoothness of the surfaces

2. Proper arrangement of frictions in their decreasing order is

a) rolling, static, sliding.

b) rolling, sliding, static.

c) sliding, static, rolling.

d) static, sliding, rolling.

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3. The increasing order of friction in the following substances is

a) sand, glass, wood. b) glass, wood, sand.

c) glass, sand, wood. d) wood, glass, sand.

II. Fill in the blanks by choosing correct words from the list given in the brackets :

(less, heat, opposite, reduce, greater, more.)

1. Friction always acts in the direction __________ to the direction of the applied force.

2. Friction produces __________.

3. Static friction is __________than the sliding friction.

4. Frictional force is __________ in smooth surfaces.

5. Lubricant __________ the friction between the surfaces in contact.

III. Match the friction managing agents given in list ‘A’ with their applications given in list ‘B’ :

A B

1. spikes a) air crafts

2. treads and groves b) rollers

3. talcum powder c) ball bearings

4. grease d) carrom board

5. stream-lining e) tyres

f) shoes

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IV. Answer the following questions :

1. What is friction? Explain how it is caused.

2. Name the two important factors which affect friction?

3. Make a list of the effects of friction.

4. Why is friction called a necessary evil?

5. State two advantages of friction.

6. State two disadvantages of friction.

7. What is a lubricant? Give two examples.

8. How does a lubricant reduce friction?

9. How can you say that sliding friction is greater than the rolling friction?

10. Explain why objects moving in fluids must have stream-line shapes.

V. Give reasons for the following :

1. A ball rolling over the ground slows down.

2. The surface of a conveyor belt is made rough and tight.

3. The worn out tyres are discarded.

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UNIT - 4ACCELERATION

After studying this unit you :

� differentiate between uniform and non-uniform motion.

� establish relation between non-uniform motion and acceleration.

� define the terms acceleration, uniform acceleration and deceleration.

� identify the acceleration in the direction opposite to the motion.

� distinguish between acceleration and deceleration.

� explain the graphical representations of accelerated motion.

� make a list of illustrations of accelerated motion in day-to-day life.

� calculate the numerical values related to acceleration.

You might have enjoyed a ride on a bicycle. While you are moving along a given direction observe your position will be changing. In other words, you will be moving with a velocity which means that there will be a change in position along a given direction.

If a body changes its position equally at equal intervals of time it is said to be moving uniformly.

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Consider the situations given.

Situation 1 : Imagine that you are riding a bicycle at a steady pace along a straight path. If you are moving with a velocity of 2 ms -1, it means that you will cover a distance of 2 metre in one second, 20 metre in ten seconds, 200 metre in hundred seconds and so on, covering equal distances in equal time intervals. So in such cases velocity does not change .

Fig. 4.2

Vel

ocit

y (m

s- 1)

time(s)

Riding a bicycle Graph showing no change in velocity over time

Fig. 4.1

If a body changes its position unequally at equal intervals of time it is said to be non uniform motion.

Situation 2 : Suppose you are

Fig. 4.3 Riding a bicycle

in a hurry! You may begin to speed up your bicycle by covering the distance more and more quickly. If you cover a distance of 2 metre in one second, 30 metre in ten seconds and 500 metre in hundred seconds, your velocity will be 2 ms -1 at the end of first second, 3 ms -1 at the end of tenth second and 5 ms -1 at the end of hundredth second.

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Here the change in position is continuously increased with respect to time. So your velocity changes in an increasing order. (See figure 4.4) Finally, when the destination is near, now you are not in a hurry, you obtain a modest push. Here the change in position is continuously decreased with respect to time. So your velocity changes in a decreasing order. (See figure 4.5)

time(s)

Vel

ocit

y (m

s-1)

time(s)

Vel

ocit

y (m

s-1)

Fig. 4.4

Graph showing increase in velocity over time

Fig. 4.5

Graph showing decrease in velocity over time

In the above situations whether velocity may increases or decreases, it keeps on changing.

What is this change in velocity over time called?

Know this :Change in velocity is the difference between initial velocity and final velocity of a body in an interval of time.

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Change in velocity with reference to time is called acceleration. Acceleration measures how quickly velocity changes, whether you are speeding up, slowing down or changing the direction, you are accelerating! So, acceleration of a body is defined as the rate of change of its velocity.

u = initial velocity, v = final velocity, t = time.

The S.I unit of velocity is ms-1(metre per second) and that of acceleration is ms-2 (metre per second square).

Know this :

Physical quantities are of two types. Vector quantities and scalar quantities. A vector quantity consists of both magnitude and direction. The magnitude tells you how much of the quantity exists. While the direction tells you which way the quantity is pointing.

Force, displacement velocity and acceleration are some of the vector quantities. Whereas length, time, mass, volume, distance travelled and speed are some of the scalar quantities which have only magnitude but not direction.

For example, if the height of a tree is 15 m (magnitude) it is not necessary to mention whether it is from top to bottom or bottom to top.

Think :It a body moves with uniform velocity its acceleration is zero ms-2. Why?

Acceleration =final velocity - initial velocitytime taken

v-ut=

Acceleration (a) = change in velocitytime taken

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Deceleration :

Consider a vehicle race. When the race is over, generally they cross the closing line and tend to attain rest. It is because the velocity is decreasing over the time and hence the acceleration is negative thus they come to a stop. We often call this process as deceleration or retardation. It is just a special type of acceleration of a body where forward velocity diminishes until come to rest.

Fig. 4.6 : Racing bikes at the closing line

The negative acceleration is called deceleration.

Deceleration = ms-2decrease in velocity

time taken

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Uniform acceleration :

Situation 3 : Consider a body moving with a velocity of 2 ms-1 at the end of 5 minutes, let its velocity be 4 ms-1 at the end of 10 minutes. Further it is 6 ms-1 at the end of 15 minutes and so on. What is the amount of increase in velocity over every 5 minutes?

Yes, here the increase in velocity during every 5 minutes is 2 ms-1 and hence the acceleration is uniform.

acce

lera

tion

(ms-2

)

time (minutes)

Fig. 4.7 Graph showing equal change

in velocity over time

Acceleration is said to be uniform if the body changes its velocity by equal amounts in equal intervals of time.

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To help you to recognize the acceleration, here are some instances of motion with and without acceleration.

Accelerated motion Non accelerated motion � The ball kicked by a foot

ball player The velocity of the ball changes from zero to its maximum. So the ball is accelerating forward.

� A scooter climbing up a smooth straight hill at a steady speed No change in velocity or direction.

� A motor bike is about to stop at a traffic signal Here velocity changes from its maximum to zero. So it is accelerating negatively (deceleration).

� A car traveling straight forward on a level road at a steady speed No change in velocity or direction.

� An elevator lift just starts to move from first floor to fifth floor Velocity is changing from zero to its maximum. So it is accelerating upward.

� An elevator lift moving straight upward at a steady speed from first floor No change in velocity or direction, hence no acceleration.

Fig. 4.8 : Elevator lift Think :

All non accelerated motions are not decelerated motions. Why?

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Worked examples :

(1) Find the acceleration gained by a body in 5 seconds if its initial velocity is 20 ms-1 and final velocity is 40 ms-1.

Solution :Data :

Initial velocity u = 20 ms-1

Final velocity v = 40 ms-1

Time interval t = 5 seconds

Acceleration a = ?

ms-2v-ut

a =

a =

a =

a =

40 ms-1 - 20ms-1

5s20ms-1

5s

4ms-2

∴ Acceleration gained by the body is 4 ms-2

(2) A motor cyclist moving with certain velocity comes to rest in 6 seconds. Calculate the initial velocity if he was decelerated by - 3 ms-2.

Solution :Data :Final velocity v = 0Time interval t = 6 secondsDeceleration (a) = - 3 ms-2 Initial velocity u = ?

Acceleration = =v-u

tFinal velocity Initial velocity

time takenms-2

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a = v - ut

-3 ms-2 =

o - u6s

- u = - 3 ms-2 X 6 s.

- u = - 18 ms-1

u = 18 ms-1

∴ Initial velocity of the motor cycle is 18 ms-1

Remember

� If a body changes its position equally at equal intervals of time it is said to be uniform motion.

� Non uniform motion of a body is the unequal change in its position at equal intervals of time.

� Change in velocity is the difference between initial velocity and final velocity of a body in an interval of time.

� Acceleration of a body is the rate of change of its velocity. � Acceleration of a body change even with the change in its

direction of motion. � Acceleration is a vector quantity having both magnitude

and direction. � Deceleration is the negative acceleration where the velocity

of a body decreases over the time interval.

� Uniform acceleration of a body is the change in velocity by equal amounts in equal intervals of time.

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Tips y Use straight and smooth roads to accelerate the vehicles.

Remember, over speed is fatal. y Avoid unnecessary braking while riding the vehicle to

maintain acceleration. y Acceleration of a body is directly proportional to the force

applied on it along the direction of motion. So apply force along the direction of your motion and gain required acceleration.

y Friction reduces the acceleration of a body. So control unwanted friction in motion.

Exercises

I. Four alternatives are given under each complete/ incomplete statement. Choose the correct answer and put a tick () mark against it :

1. If a body moves with uniform velocity then its acceleration isa) uniform b) nonuniformc) zero d) negative

2. Acceleration of a body is the rate to change of a) distance travelled b) speedc) displacement d) velocity

3. The acceleration of a body is 3 ms-2. This means that the velocity changes in every two seconds by

a) 2 ms-1 b) 3 ms-1

c) 6 ms-1 d) 9 ms-1

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4. The velocity time graph implies that

time(s)

velo

city

(ms-1

)

0

the body

a) moves with constant velocity

b) has an initial velocity and uniformly decelerated to attain rest

c) starts from rest and has a uniform acceleration

d) has an initial velocity and non uniform acceleration

5. A physical quantity having both magnitude and direction is

a) time b) acceleration

c) speed d) distance travelled

II. Fill in the blanks by choosing correct words from the list given in brackets :

(deceleration, zero, ms-2, magnitude, 5 ms-1, acceleration)

1. The S.I. unit of acceleration is ___________ .

2. The negative acceleration is called ___________ .

3. If a moving body comes to a stop, its final velocity is___________ .

4. The velocity gained in 5 seconds by a body moving with uniform acceleration of 1 ms-2 is___________ .

5. A scalar quantity has only___________ .

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III. Match the following :

A B

At definite time intervals:

1. equal change in position a) uniform acceleration

2. unequal change in position b) deceleration

3. increase in velocity c) nonuniform acceleration

4. decrease in velocity d) nonuniform motion

5. equal change in velocity e) acceleration

f) uniform motion

IV. Answer the following questions :

1. State the difference between uniform and nonuniform

motion.

2. Define acceleration with an example.

3. Distinguish between acceleration and deceleration.

4. What is meant by uniform acceleration? State its

S.I. unit.

5. Explain the term deceleration with an example.

6. Calculate the acceleration of a body if it starts from

rest and attains the velocity 20 ms-1 in 10 seconds.

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7. An object moving at a velocity 24 ms-1 is brought to a halt in 8 seconds by applying a force in opposite direction to the motion. Calculate the acceleration.

8. If a vehicle is accelerated to 5 ms-2, how much time does it take to attain a velocity of 27 ms-1 which initially starts with 2 ms-1 ?

9. What does it imply and why? If :

a) acceleration of a body is zero ms-2

b) initial velocity of a body is zero ms-1

c) final velocity of a body is zero ms-1

V. Give reasons for the following :

1. A car travelling on an uneven mud road is an example of non-uniform motion.

2. Acceleration and deceleration have the same units yet they have difference.

Project Work

� Represent the following data in a velocity time graph and determine the type of acceleration.

Velocity (ms-1) 5 10 15 20 25 30

Time (s) 0 10 20 30 40 50

RR

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UNIT - 5ENErgy

After studying this unit you : � recognise the components of mechanical energy. � define potential energy and kinetic energy. � reason out the cause for potential energy and kinetic

energy of a body. � give examples for kinetic energy and potential energy. � differentiate between kinetic energy and potential energy. � make a list of the uses of kinetic energy and potential

energy in our day-to-day life. � establish relation between mass and velocity, mass

acceleration and height, mass force and acceleration, work, force and displacement of a body.

� identify the factors which affect the amount of work done by a body.

� calculate the amount of work done by a body in terms of force and displacement.

� make a list of the units used to represent energy, force, work, and displacement.

You know that energy is the capacity of a body to do work. Energy is measured by the work that the body can do. Energy exists in many forms such as heat, light, sound, wind, electricity, chemical energy, solar energy, magnetic energy and nuclear energy etc.

Energy exists prominently in the mechanical form which makes the body to work by virtue of its position or motion.

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Activity 5.1 : Consider the following Pictorial examples. List A List B

Arrow on a stretched bow.

Wound up spring of a doll.

Rock on a hill top.

Water stored in a dam.

Arrow in motion

Clapping doll

Rolling rock down the hill.

Running stream of water from the dam.

Fig. 5.1

In the above examples the mechanical energy of the items in list-A is in stored form by virtue of their position.

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But the energy acquired by the items in list-B is in the form of motion by virtue of change in position. Let us see how the position and change in position of a body leads to potential energy and kinetic energy respectively.

1. Potential energy : The energy possessed by a body by virtue of its position

is called potential energy.

Know this :The word potential comes from a Latin word which means to be able.

Let us try the following activities to understand potential energy.

Activity 5.2 : Take a catapult.

Fig. 5.2 : Stretched catapault

Hold the rubber slings at its ends, and stretch them as shown in the figure. Do you feel a pull back? Yes, they tend to regain their original position.A catapult acquires potential energy at a stretched position.

Activity 5.3 : Take a spring.

Fig. 5.3 Compressed spring on a table.

Put it vertically on a table and compress the spring vertically downward. Do you feel a push back? Yes it tends to regain its original position. Generally a spring acquires Potential energy at a compressed or stretched position. When this energy is released an equalent amount of work can be done. The potential energy of the compressed spring is used for firing a bullet from a gun.

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Think :Elasticity or position sustainity of a body is the real cause of its potential energy.

Know this : y An object at rest can have potential

Fig. 5.4 : Uploading wooden

logs to a truck

energy due to its raised position.

y The higher an object is raised above the ground level, the greater is its potential energy.

y Greater the mass of the body, the greater is the potential energy.

Expression for potential energy of a body at height ‘h’

Consider a body of mass m kg. If it

Fig. 5.5 : A sand bag of m kg lifted to

a height h metre

is lifted through a height h metre from the ground level, work is done on the body against the gravitational force g. The amount of work done in doing so is mgh joules(J) which is stored in the body as potential energy. This is calculated by the formula

P.E = mgh J

Know this :Work done = (force) (displacement)Potential energy = (mass × acceleration due to gravity) (height) P.E = (m × g) × h ∴ P.E = mgh here g = acceleration due to gravity. g = 9.8 ms-2

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2. Kinetic energy :

The energy possessed by a body by virtue of its motion is called kinetic energy.

Know this :The word kinetic comes from a Greek word which means motion.

Kinetic energy is measured by the amount of work the body can do before coming to rest. A moving vehicle, a moving bullet, flowing water, moving air, a falling body, a swinging pendulum, a moving ball, all of these possess kinetic energy.

Know this :In hydro power stations the kinetic energy of the falling water rotates the turbine connected to an electric generator, thus the electrical energy is generated by the kinetic energy of water.

Try the following activities to understand kinetic energy.

Activity 5.4 : Let us play the game of carrom. You set all the coins in the

Fig. 5.6 : Striker making the coins move

centre of the board. Hit them with the help of a striker. What happens? The striker makes the coins move because of its kinetic energy due to motion.

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Activity 5.5 : Have you played cricket? Take a plastic ball and a

Fig 5.7 : Throwing a ball towards stumps

rubber ball of same size. Throw them at the stumps one after the other with the same force. Which ball is more likely to hit them harder? Obviously the rubber ball, because it is heavier. Thus the rubber ball possess more kinetic energy than the plastic ball.

Activity 5.6 : Take a

Fig. 5.8 Rolling inclined plane experiment

used battery cell and an empty match box. Place the match box at the foot of an inclined plane, as shown in the figure inclined at small height. Roll the battery cell down the inclined plane so as to hit the match box. The kinetic energy of the rolling cell displaces the match box. Measure the displacement. Now raise the inclination so that to make it more steep. Let the cell roll down again and hit the match box with more speed. Measure the displacement. Raise the inclination and repeat the activity. What is your observation?

From the above activities (5.4, 5.5 and 5.6) we can conclude that :

1. Bodies in motion have kinetic energy.2. If two bodies of same size and different mass are

travelling at the same speed then the body of greater mass has greater kinetic energy.

3. If the speed of a body increases, its kinetic energy also increases and if the speed decreases its kinetic energy also decreases.

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Expression for kinetic energy :Consider a body mass m kg moving with the velocity v

ms-1. If a constant force F Newton is applied against the motion of the body to bring it to rest, the work done is equal to its kinetic energy.

This is calculated by the formula

KE mv joules21 2=

Equation for force :

If a body of mass m kg having an acceleration a ms-2, then its force F is represented by an equation.

F = m.a N

Work :Consider the following example.

If a man fails to lift a heavy stone no

Fig. 5.9 A man lifting a

heavy stone

work is said to be done. But certainly work is said to be done if he lifts it with his full effort. Do you know why?

In an ordinary sense, performing an activity is commonly considered as work. But work has unique meaning. Work is said to be done only if the force displaces the body in its own direction of action.

Note :No work when there is no displacement.No displacement when there is no force.

Activity 5.7 : Make a list of the situations where work is done by the force applied. Identify the force being used and the displacement caused.

J

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Factors affecting the work :Activity 5.8 : Ask your physical education teacher to conduct a sport event, say disc throw. Throw the disc with a

Fig. 5.10 : Throwing a disc

possible force and measure the displacement. Repeat the throws gradually increasing the applied force and note down the displacements. What do you observe? It is very clear that the magnitude of displacement is increasing over the increase in the magnitude of force applied.

Hence force and displacement are the factors which affect the work.

Note :Greater is the displacement, greater is the work.

Measurement of work :

If F is the force acting

Fig. 5.11

on a body and S is the distance travelled by a body in the direction of force, then work done by the force in moving a body is equal to product of the magnitude of force and the distance travelled by a body in the direction of force.

Work = Force × displacement along the direction of force.

W = F x s

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Worked examples :

(1) If a force of 10 newton moves a body through a distance of 4 metre, calculate the work done in the direction of force.

Solution :

Data : F = 10 N

Know this :In S.I. System the unit of force is newton (N) and unit of displacement is metre (m). So unit of work is newton × metre (joule).

1 joule = 1 newton metre

s = 4 m

W = ?

W = F s

W = 10 N × 4 m

W = 40 J.

(2) Calculate the displacement of an object in the direction of force applied if 40 joule work is done by the force of 5 N.

Solution :

Data : F = 5 N

W = 40 J

s = ?

W = F s

s = FW

s =

s = 8 m

40 Nm5 N

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remember

� A body can have two types of energy _ Potential and Kinetic.

� Potential energy and Kinetic energy taken together constitute mechanical energy.

� The energy possessed by a body by virtue of its position or shape is called potential energy.

� A moving object possess kinetic energy.

� Potential energy depends upon the mass of the body and the height to which it is raised.

� Kinetic energy depends upon the mass of the body and its velocity.

� Potential energy _ P.E = mgh J.

� Kinetic energy _ K.E = 21 mv2 J.

� Force _ F = ma N

� Work done _ W = Fs J.

� Potential energy of a body can be increased by raising it to more height or by bringing in to a definite shape.

� Kinetic energy of a body can be increased by increasing the force applied and reducing the friction.

Tips

y Do not step out suddenly from a moving vehicle. Other wise kinetic energy acquired by your body will make you to fell down.

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y Try to gain more kinetic energy by running fast before jumping in athletic events, such as long jump and high jump.

y Do not waste energy as it can be referred as stored work.

Exercises

I. Four alternatives are given under each complete/ incomplete statement. Choose the correct answer and put a tick () mark against it :

1. Mechanical energy is the combination of

a) potential energy and kinetic energy.

b) solar energy and heat energy.

c) wind energy and electrical energy.

d) water energy and bio energy.

2. Potential energy of a body increases with increase in

a) mass of the body.

b) height of the body.

c) both mass and height of the body.

d) speed of the body.

3. The object which has greater kinetic energy is :

a) mass = 3 kg, velocity = 4 ms-1.

b) mass = 5 kg, velocity = 6 ms-1.

c) mass = 8 kg, velocity = 2 ms-1.

d) mass = 10 kg, velocity = 3 ms-1.

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4. The S.I. unit of work is

a) newton b) watt

c) joule d) metre

5. The work is said to be done when a body is

a) at rest

b) displaced along the force applied

c) stationary even under an applied force

d) under a pair of equal and opposite forces

II. Fill in the blanks by choosing correct words from the list given in brackets :

(kinetic energy, force, rest, mass, displacement, potential energy.)

1. Water stored in an over head tank is an example for __________.

2. Rolling rock down the hill is an example for __________.

3. Kinetic energy is measured by the amount of work the body can do before coming to __________.

4. If two bodies are moving at the same speed, the body with the greater __________ has greater kinetic energy.

5. Amount of work done increases with increase in the magnitude of __________.

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III. Match the physical quantities given in list ‘A’ with their corresponding formula given in list ‘B’ : A B1. mechanical energy (M.E) a) m х a2. potential Energy (P.E) b) u + at3. kinetic Energy (K.E) c) F х S4. force (F) d) mgh

5. work (W) e) KE + PE

f) mv21 2 mv2

IV. Answer the following questions :

1. What are the two forms of mechanical energy?

2. What do you mean by potential energy? Give two examples.

3. What is kinetic energy? Give two examples.

4. On what factors do the potential energy of a body depend?

5. When does a body is said to possess kinetic energy?

6. Differentiate between potential energy and kinetic energy.

7. Name two factors which affect the work done by a body.

8. In which case do we consider the potential energy to be equal to zero?

9. What is the relationship between kinetic energy of a body to its mass and speed?

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10. Calculate the amount of work done when you push a table through a displacement of 8.5 m, with an applied force of 20 N.

11. What is the displacement a toy car when 30 J of work is done by an applied force of 6 N?

12. 68 J of work is done by a compressed spring when released. If it displaces an object through 8 m, calculate the force excerted by the spring.

V. give reasons for the following :

1. Flowing water is used to generate hydro electricity.

2. A deformed spring possesses potential energy.

3. Kinetic energy of a body at rest is assumed to be equal to zero.

Project Work

� Prepare a spring and a thread pendulums. Observe their oscillations. Give a brief description about of the conversion of energy occurring from potential energy to kinetic energy and kinetic energy to potential energy.

RR

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UNIT - 6ProPerTIes of solIds, lIqUIds aNd gases

after studying this unit you :

� reason out the differences in molecular arrangement in solids, liquids and gases.

� state the properties of solids, liquids and gases through activities.

� compare the properties of solids, liquids and gases.

� develop the skill to conduct experiments.

You have observed wood, stone, water, milk, smoke and fog in your surroundings. These things are in different states of matter. What are these physical states of matter? They are solids, liquids or gases. They are quite different too. What is the reason for these different states of matter?

The physical states of matter are due to the arrangement of molecules in them. They also have differences in their properties.

Solid Liquid Gas

Fig. 6.1 Arrangement of molecules in solid, liquid and gas

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1st Set BW Proof : 29-08-2013 : 001 to 139 (Total 141 Pages) : Print Given : suguna

2nd Set BW Proof : 29-09-2013 : 001 to 139 (Total 141 Pages) : Print Given : suguna

3rd Set BW Proof : 7-10-2013 : 001 to 139 (Total 141 Pages) : Print Given : suguna

4th Set BW Proof : 12-10-2013 : 001 to 139 (Total 141 Pages) : Print Given : suguna

5th Set BW Proof : 09-01-2014 : 001 to 139 (Total 141 Pages) : Print Given : suguna

6th Set Clr Proof : 30-01-2014 : 001 to 139 (Total 141 Pages) : Print Given : suguna

Extra BW / Clr Proof : 00-00-2013 : 000 to 000 (Total 000 Pages) : Print Given : Operator

Finalised Draft Print : 00-00-2013 : 000 to 000 (Total 000 Pages) : Print Given : Operator

Know this :Plasma, the fourth state of matter is an ionized gas. It is found in stars, lightning, auroras, flames and some types of X-rays.

Fig. 6.2 : Lightning

Properties of solids :Activity 6.1 : Take a fairly big pebble and try to fit it into a small glass. Will the pebble fit into the glass? It is not possible how ever much you try. This is because the pebble is a solid and is rigid. This shows that solids have a definite shape.

Activity 6.2 : Take a measuring jar and pour 100 ml of water into it. Tie a solid to one end of a thread andimmerse into the measuring jar in such a way that it does not touch the walls of the jar. What do you observe? The water level in the measuring jar rises. Note the rise in water. Note that a larger solid displaces more water level. This shows that solids occupy space and have a definite volume.

50 ml

150 ml

250 ml

50 ml

150 ml

250 ml

Fig. 6.3 Solids occupy space

and have definite volume

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You would have noticed how a vegetable vendor measures the quantity of vegetables you ask for. If you ask for 1 kg of potatoes, what does he do? He will take the 1 kg weight and place it in a pan of his common balance. What happens to the balance? The pan with the 1 kg weight tilts down and the empty pan goes up. This shows that solids have weight.

Take a piece of thread and pull it apart. Take a porceline cup and drop it. What happens? The thread gets cut and cup gets broken.Some solids break.

Is it easier to cut a rubber ball than a piece of wood? Yes. This tells us that some solids are soft while some are hard.

Know this :A sponge is a solid, yet it can be compressed, why? A sponge has pores filled with air. When compressed, the air in the pores escapes. It can be compressed only to its existing volume. Its density does not change.

Some solids can be compressed a little depending on the material they are made up of.experiment :Ball and ring experiment :

Take an iron ball and the ring

iron ball

after heating

before heating

Fig. 6.4 Solids expand on heating

in which the iron ball pass through easily. Pass the ball through the ring. It passes through the ring easily. Now heat the ball for about 5 minutes. Try to pass the ball through the ring. What happens? The ball does not pass through the ring. This shows that solids expand on heating.

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1st Set BW Proof : 29-08-2013 : 001 to 139 (Total 141 Pages) : Print Given : suguna

2nd Set BW Proof : 29-09-2013 : 001 to 139 (Total 141 Pages) : Print Given : suguna

3rd Set BW Proof : 7-10-2013 : 001 to 139 (Total 141 Pages) : Print Given : suguna

4th Set BW Proof : 12-10-2013 : 001 to 139 (Total 141 Pages) : Print Given : suguna

5th Set BW Proof : 09-01-2014 : 001 to 139 (Total 141 Pages) : Print Given : suguna

6th Set Clr Proof : 30-01-2014 : 001 to 139 (Total 141 Pages) : Print Given : suguna

Extra BW / Clr Proof : 00-00-2013 : 000 to 000 (Total 000 Pages) : Print Given : Operator

Finalised Draft Print : 00-00-2013 : 000 to 000 (Total 000 Pages) : Print Given : Operator

Ice melts at 00C and iron melts at 15400C. Solids have a definite melting point.Properties of liquids :Activity 6.3 : Lift a small empty bucket. Now fill the bucket with water and lift. What do you feel? The bucket when filled with water becomes heavier than the empty bucket. This shows us that water has mass.

Activity 6.4 : Pour water into a

Fig. 6.5 Measuring jar

containing water

measuring jar and measure the quantity of water in it. If we are able to measure the quantity of water it means water is a liquid having volume. Observe that water could be poured into the jar and it occupies space.

Activity 6.5 : Pour 100 ml of any liquid into a measuring jar, a conical flask and a beaker. Observe the shape taken by the liquid in all the three vessels. Are they same? No. Water take the shape of the containers it is poured into. That is, water do not have a definite shape.

Fig. 6.6 : Liquids take the shape of the containers they are kept in

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Properties of gases :

Activity 6.6 : Tie a balloon filled with air at one end of a scale and another balloon which is not filled with air at the other end of the same scale. Balance the scale at the centre with your finger. What do you observe? The scale tilts to the side of the inflated balloon. This shows that air has mass.

Activity 6.7 : Fill air into a balloon, football and a tyre tube. Observe their shapes. Do they all have same shape? No. Gases take the shape of the object they are filled into. They also occupy the maximum space as they spread. Gases do not have definite shape.

Gases can be stored in cylinders and transported as they can be compressed.

Think :Now a days helium gas is used to fill balloons instead

of hydrogen gas. Why?

experiment :

(Teacher assistance required to conduct this experiment)

Take a clean, dry, cylindrical transparent tube opened at both ends. Take two cotton dabs one dipped in hydrochloric acid and the other in ammonium hydroxide. Insert them at either ends of the tube and plug the tube ends using corks. Slightly heat the tube. What do you observe? A white ring is formed inside the tube. This white ring is ammonium chloride formed by the fusion of the diffused vapours of ammonium hydroxide and hydrochloric acid. This experiment shows that gases diffuse.

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1st Set BW Proof : 29-08-2013 : 001 to 139 (Total 141 Pages) : Print Given : suguna

2nd Set BW Proof : 29-09-2013 : 001 to 139 (Total 141 Pages) : Print Given : suguna

3rd Set BW Proof : 7-10-2013 : 001 to 139 (Total 141 Pages) : Print Given : suguna

4th Set BW Proof : 12-10-2013 : 001 to 139 (Total 141 Pages) : Print Given : suguna

5th Set BW Proof : 09-01-2014 : 001 to 139 (Total 141 Pages) : Print Given : suguna

6th Set Clr Proof : 30-01-2014 : 001 to 139 (Total 141 Pages) : Print Given : suguna

Extra BW / Clr Proof : 00-00-2013 : 000 to 000 (Total 000 Pages) : Print Given : Operator

Finalised Draft Print : 00-00-2013 : 000 to 000 (Total 000 Pages) : Print Given : Operator

Fig. 6.7 : Gases diffuse

burners

white ring

cotton piece with ammonium hydroxide

cotton piece with hydrochloric acid

The process of spreading of vapours of camphor, the smell of flowers, smell of good food, a lighted agarbathi or perfume through air is called diffusion.

remember

� Physical states of matter are due to their molecular arrangement.

� The four states of matter are solid, liquid, gas and plasma state.

� Solids have a definite shape, volume and occupy space.

� Solids have a definite melting point and mass.

� Solids expand on heating.

� Solids could be soft or hard and could break.

� Liquids have definite mass, occupy space and they flow.

� Liquids do not have a definite shape.

� Liquids spread when spilt.

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� Gases have mass and occupy space.

� Gases do not have a definite shape and volume.

� Gases can be compressed to a large extent.

� Gases diffuse.

Tips

y Solids, liquids and gases must be handled carefully.

y Wherever the liquids are spilt, care should be taken.

exercises

I. Underline the word which does not belong to the group :

1. carbon dioxide, carbon, hydrogen, carbon monoxide.

2. porceline, wood, iron, milk.

II. give two examples for each of the following :

1. Substances which have a definite shape.

2. Substances which flow.

3. Substances which are invisible but diffuse.

III. answer the following questions :

1. What is the reason for the different states of matter?

2. How are the properties of a brick different from that of air?

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1st Set BW Proof : 29-08-2013 : 001 to 139 (Total 141 Pages) : Print Given : suguna

2nd Set BW Proof : 29-09-2013 : 001 to 139 (Total 141 Pages) : Print Given : suguna

3rd Set BW Proof : 7-10-2013 : 001 to 139 (Total 141 Pages) : Print Given : suguna

4th Set BW Proof : 12-10-2013 : 001 to 139 (Total 141 Pages) : Print Given : suguna

5th Set BW Proof : 09-01-2014 : 001 to 139 (Total 141 Pages) : Print Given : suguna

6th Set Clr Proof : 30-01-2014 : 001 to 139 (Total 141 Pages) : Print Given : suguna

Extra BW / Clr Proof : 00-00-2013 : 000 to 000 (Total 000 Pages) : Print Given : Operator

Finalised Draft Print : 00-00-2013 : 000 to 000 (Total 000 Pages) : Print Given : Operator

3. Write two similarities between the properties of gases and liquids.

4. What is diffusion? Can liquids diffuse?

5. Conduct an experiment to show that gases diffuse and explain it.

6. Conduct an experiment to show that solids expand on heating and explain it.

IV. give reasons for the following :

1. Solids have a definite shape.

2. Liquids are capable of changing their shape.

3. Camphor could be smelt from a short distance.

4. Gases can be compressed.

5. A bucket filled with water will be heavier than an empty bucket.

RR

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UNIT - 7HeaT aNd TemperaTUre

after studying this unit you : � define heat and temperature. � make a list of the differences between heat and

temperature. � explain the construction of a laboratory thermometer. � develop the skill of drawing the diagram of a lab

thermometer. � explain the construction of a clinical thermometer. � develop the skill of drawing the diagram of a clinical

thermometer. � measure the temperature using lab thermometer and

clinical thermometer.

Have you experienced the weather changes that happen from morning till evening? When do you feel cool and when do you feel warmer? Why does it happen?

We feel cool in the morning and in the evening. We feel warmer during mid day. This is because of the variation in the sun’s radiations which we receive.

Rubbing the palms and folding the body are very common during cold season. While rubbing the palms muscular energy gets converted into kinetic energy of the palms, which leads to friction, then in turn produces heat.

While cleaning utensils and washing clothes, if you use hot water, cleaning will be easier. The dirt goes off easily as the hot water has more energy than the cold water.

Think : y How does a petrol engine or a diesel engine work? y Why is the dissolution faster in hot water than in

cold water?

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Activity 7.1 : Take a beaker containing cold water and another one containing hot water. Put a drop of ink to each of them.

hot watercold water

ink drop

Fig. 7.1

What differences do you observe in two beakers?

In the beaker containing cold water, ink spreads slowly, whereas in the beaker containing hot water, ink spreads faster. The spreading of ink takes place due to the movement of water molecules.

The atoms and molecules in matter are in continuous motion. So they possess kinetic energy.

The sum of kinetic energy of all the molecules in a matter is called heat.

As heat is a form of energy, the unit of energy itself is the unit of heat. So, S.I. unit of heat is joule (J).

Sources of heat :

1. Sun is the primary source of heat energy.

2. Heat is obtained by burning fuel. example : wood, kerosene, L.P.G., coal and petrol

are some commonly used fuel.

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3. Electricity produces heat. example : electric iron, electric boiler etc., are some

electrical appliances which convert electrical energy into heat.

Temperature :

Activity 7.2 : Touch a beaker containing cold water. What do you feel? Heat the beaker for 2 to 3 minutes. Now touch the beaker. What do you feel?

In the above activity, we feel cold while we touch the beaker before heating it. We feel hot after heating it. Heat changes a cold body into hot body. Heating increases the degree of hotness of any system.

The measure of degree of hotness of a body is called temperature.

While heating, energy of the system increases. So the kinetic energies of the molecules increase. Thus the average kinetic energy of the molecules also increases.

Temperature is defined as the average kinetic energy of the molecules.

We understand from the above activity, heat is the cause of increases in temperature, and temperature is the effect of heat.

Average Number of oleculesSum of inetic energy of all themoleculeskinetic energy m

k=

Activity 7.3 : Dip a small piece of hot iron into a small quantity of cold water in a cup. After sometime the piece of iron becomes cold and water becomes warm. The heat from the piece of iron is transferred to water.

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Heat transfers from hot body to cold body.differences between heat and temperature :

Heat Temperature

1. Heat is a form of energy. 1. Temperature is the measure of degree of hotness.

2. S.I. Unit of heat J (joule) 2. S.I. Unit of temperature is K (kelvin).

3. The sum of kinetic energy of all the molecules in a matter.

3. The average kinetic energy of the molecules.

In our day to day life, we come across a number of objects. Some of them are hot and some of them are cold.

Activity 7.4 : Classify the following substances into hot and cold objects and write them in the table given.

ice cream, metal handle of a frying pan, glucose solution, cooker consisting of steam,

juice kept in the refrigerator, boiling milk.

Hot substance Cold substance

We see that some objects are cold and some are hot. Some objects are hotter than others and some are colder than others. How do we decide which object is hotter than the other?

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Activity 7.5 : Take three large beakers. Name them as 1, 2 and 3. Fill some ice cold water in beaker 1. Fill some hot water in beaker 2. Mix some ice cold water and hot water in beaker 3. Dip your left hand in beaker 1, right hand in beaker 2. Keep the hands for 2 - 3 minutes. Put both the hands simultaneously in beaker 3.

Ice cold water Hot waterIce cold water and hot water

1 2 3

Fig. 7.2

What do you feel? Do both the hands get the same feeling?No, both the hands do not get the same feeling. The left

hand feels hot and the right hand feels cold.In such a situation, it is difficult to decide, how hot an

object is?A reliable measure of the degree of hotness of an object is

temperature.measurement of Temperature :

Temperature is measured by a device called thermometer.Thermometer is an instrument that measures the

temperature of a system quantitatively.There are different types of thermometers which are

classified on the basis of their application and working principle. The most commonly known thermometers are laboratory thermometer and clinical thermometer.

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1. Laboratory thermometer : A labora to ry the rmomete r

Fig. 7.3 Laboratory thermometers

consists of a thick walled glass capillary. One end of it has a thin walled glass bulb filled with mercury or red coloured alcohol. The air inside the capillary is removed and the other end is closed. The capillary is fitted inside a glass tube. The whole length is graduated suitable to enable us to measure the temperature.

Activity 7.6 : Measure the temperature of different substances using laboratory thermometer.2. Clinical thermometer :

A clinical thermometer is designed for clinical use of human and animals. It is made of a fine capillary with a bulb filled with mercury at one end. Near the bulb i t has a narrow bend known as constriction. The constriction prevents the back flow of mercury when it is taken out of a patient’s mouth or armpit. Before using it again, the thermometer is jerked so that the mercury flows back into the bulb.

To reduce the risk of cross - contamination between patients, it has to be sterilized after each use.

The normal temperature of human body is about 98.60F (370 C). Our body temperature cannot fall below 950 F or rise

Fig. 7.4 : Clinical thermometer

constriction

mercury bulb

scale

scale

mercury

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above 1080 F. Hence the range of clinical thermometer is between 950 F and 1080 F.(350 to 42.20C)

F= Fahrenheit, C=Celcius

Activity 7.7 : Take a clinical thermometer from your lab. Measure your body temperature. Measure the body temperature of your friends. Follow the safety rules.differences between laboratory thermometer and clinical thermometer :

Laboratory thermometer Clinical thermometer

1. Used to measure the temperature in the laboratory.

1. Used to measure the temperature of human body and animal body.

2. Range of temperature is from - 300 C to 1100 C.

2. Range of temperature is from 950 F to 1080 F. (35o C to 42.2o C)

3. Constriction is absent. 3. Constriction is present.Now a days many other advanced types of thermometers

are used. For example, digital thermometer, constant volume gas thermometer, platinum resistance thermometer, thermoelectric thermometer etc.

remember � The sum of kinetic energy of all the molecules in a matter

is called heat. � Heat is a form of energy. � The measure of degree of heat of a body is called

temperature. It is the average kinetic energy of the molecules.

� Temperature is measured in terms of Kelvin. � The thermometer is an instrument that measures the

temperature of a system quantitatively. � A laboratory thermometer is used to measure the

temperature of different systems in the laboratory.

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� A clinical thermometer consists of constriction. � A clinical thermometer is used to measure the temperature

of human beings and animals.

Tips y Do not wash a clinical thermometer using hot water. y Sterilize a clinical thermometer before using.

exercisesI. Fill in the blanks with suitable words :

1. The primary source of heat is ____________.2. In hot water the movement of molecules is ____________.3. Temperature is measured by ____________.4. The S.I unit of heat is ____________.5. The S.I unit of temperature is ____________.

II. answer the following questions :1. Write the differences between heat and temperature.2. Draw a neat labelled diagram of a laboratory

thermometer.3. Draw a neat labelled diagram of a clinical thermometer.4. Write the differences between a laboratory thermometer

and clinical thermometer.5. Heat transfers from a hot body to a cold body. Give an

illustration.project work

� Give the equivalent value of temperature of 0o C and

100o C in Fahrenheit.

� Measure and make a list of atmospheric temperature for a week.

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UNIT - 8ACIDS, BASES AND SALTS

After studying this unit you : � name some common acids, bases and salts. � explain the meaning of acids, bases and salts. � identify organic and mineral acids. � define acids and bases. � list out and explain the physical and chemical properties

of acids and bases with activities and experiments. � make a list of the properties of salts. � develop the skill in drawing neat diagrams showing the

experimental set up related to acids and bases. � differentiate between the properties of acids and bases. � make a list of the uses of acids, bases and salts. � define indicators. � explain the meaning of neutralization and formation of

salts. � explain the meaning of pH value, what does it indicate

and its importance in life.

You have already learnt the meaning of compounds. You also know the names and formulae of some of them. Can you name some compounds? Some of these compounds are naturally occurring and are essential for life. Chemical compounds are broadly classified into three groups. They are -

1. Acids.

2. Bases.

3. Salts.

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Let us now study about acids, bases and salts in detail.

1. Acids :

The food that we eat daily consists of cereals, vegetables, fruits etc.

Activity 8.1 : Squeeze out

Fig. 8.1 : Lime is sour to taste

the juice of a lime and taste a drop of it. What does it taste like? It is sour. This sour taste is due to the presence of a chemical compound called Citric acid. Can you name some other edibles that taste sour?

Know this :The word acid comes, from the Latin word acidus which means sour.

Most citrus fruits like lemon, orange, gooseberry and grapes are sources of vitamin C. Vitamin C is chemically called ascorbic acid. Vinegar, tamarind, milk, curd and tomato also contain acids.

When a person is stung by

Fig. 8.2 : Red ant and bee

bees or bitten by red ants, he e xpe r i enc e s a bu rn ing sensation on his skin. Do you know why? This is because these insects inject an acid into the body when they bite or sting. This acid is formic acid.

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Types of acids :Acids can be classified into two groups. They are organic

(carbonic) acids and mineral (acarbonic) acids.

1. Organic acids :Acids that occur naturally are called organic acids. The

table given below gives some naturally occurring acids and what they occur in.

With suitable reference fill in the blanks to complete the table.

sl.No. Organic Acid Occurs in

1. Citric acid and ascorbic acid lemon, orange

2. Tartaric acid tamarind, unripe mango, grapes

3. Lactic acid milk

4. Oxalic acid

5. Folic acid

6. Acetic acid

7. Tannic acid

8. Malic acid

Know this :Tartaric acid is used in making jams and carbonated grape beverages. It cleans and polishes metals, hence tamarind is used while washing and cleaning brass vessels.

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2. Mineral acids (inorganic acids) :

Mineral acids are made or prepared from minerals present in the earth. The common mineral acids are sulphuric acid (H2SO4), hydrochloric acid (HCl) and nitric acid (HNO3).

An acid has two parts - 1) the hydrogen part and 2) the acid radical part. This can be understood from the table given below.

Acid Hydrogen part Radical Part

HCl H+ Cl_

H2SO4 2H+ SO4

_ _

When acids dissolve in water they split up into their hydrogen part and radical part.

Know this :A radical is a charged group of atoms.

HCldissolves in H2O H+ + Cl

_

hydrogen ion

chlorideion

H2SO4

dissolves in H2O 2H+ + hydrogen

ionsulphate

ion

SO4

_ _

In the above examples we see that when acids dissolve in water, they give a positive hydrogen ion.

An acid is a compound which when dissolved in water gives only hydrogen ions (H+) as the positive ion.

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Properties of acids :Physical properties of acids :

1. Taste : Acids are sour to taste.

2. conductivity : A few drops

caution ! � Do not taste any

acid directly.

� Do not add water to acids.

of an acid in water makes water a good conductor of electricity.

3. solubility : Acids are soluble in water. Acids should be added to water drop by drop with constant stirring. The beaker containing this solution becomes hot as it is an exothermic reaction.

corrosiveness :

Activity 8.2 : Carefully put

Fig. 8.3 Acids are corrosive

a few drops of (concentrated) sulphuric acid on a piece of cloth. What do you observe? The acid destroys the cloth creating a hole. Acids can destroy paper, wood, metals and cause burns on skin. Most acids are corrosive in nature.

Know this :Acids are not stored in metal containers. Acids corrode metals like iron and aluminium. So they are not stored in metal containers but are safe to be stored in glass containers.

litmus effect :

Activity 8.3 : Squeeze out the

Fig. 8.4 : Blue litmus paper with a drop of acid

juice of a lime into a bowl. Dip a blue litmus paper into it. What do you observe? Acids turn blue litmus red.

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Know this :

Fig. 8.5 : Johann Rudolf Glanber

Johann Rudolf Glauber was born in 1604 in Germany. He was an alchemist and chemist. Some science historians described him as one of the very first chemical engineers. He was known to have supplied medicines and provided medical treatment to the poor. He improved the process for the manufacture of nitric acid and was the first to produce hydrochloric acid.

Johann Rudolf Glauber was known to have manufactured sodium sulphate which he called sal mirabilis meaning wonderful salt. It was later known as glauber’s salt after him.

chemical Properties of acids :

Fig. 8.6 : Reaction of magnesium wire with HCl

producing hydrogen

burning splinter

magnesium wirehydrochloric acid

1. Reaction of acids with metals : experiment : Take dilute

hydrochloric acid in a test tube and put two or three strips of magnesium wire into it. What do you observe? A gas is liberated. Bring a burning splinter near the mouth of the test tube. The gas burns with a POP sound. This gas is hydrogen.

Some metals react with dilute acids to form salt and liberate hydrogen.

Metal + acid → salt + hydrogen (↑)

Know this :Salt here does not refer to common salt (NaCl). It is the compound formed when acids react with elements and compounds.

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Example :

a) Magnesium + Hydrochloric acid → Magnesium chloride + Hydrogen (↑)

b) Zinc + Sulphuric acid → Zinc sulphate + Hydrogen(↑)

Metals like sodium, potassium and calcium react violently with dilute acids.

Metals like gold, silver and copper are less reactive metals as they cannot replace the hydrogen atom from acids.

2. Reaction of acids with carbonates and bicarbonates :

Experiment :

Take about 0.5 g of calcium carbonate(CaCO3) in a test tube and close it with a two holed cork. Insert a funnel and a delivery tube as shown in the figure.

delivery tube

Calcium Hydroxide

Hydrochloric acid

Calcium Carbonate

Carbon dioxide gas

funnel

Fig. 8.7 : Reaction of calcium carbonate with HCl producing CO2

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Take a small test tube containing lime water or calcium hydroxide- Ca(OH)2 and place it at the end of the delivery tube as shown in the figure.

Pour dilute hydrochloric acid (HCl) into the test tube through the funnel. What do you observe? A brisk effervescence is observed. This evolved gas passes into the lime water. What do you observe now? The lime water turns milky. The gas evolved is carbon dioxide (CO2). Carbon dioxide turns lime water milky.Metal carbonates/ bicarbonates + Acid → Salt + Carbon dioxide ↑ + Water.example :

a) Calcium carbonate + Hydrochloric acid → Calcium chloride + Water + Carbon dioxide ↑.

b) Sodium bicarbonate + Hydrochloric acid → Sodium chloride + Water + Carbon dioxide ↑.

Know this :The reaction of sodium carbonate with sulphuric acid is used to prepare carbon dioxide in the laboratory.

Acids are widely used in our homes and in industries.Uses of acids :1. Hydrochloric acid (Hcl) is used :

y to manufacture glue. y to purify common salt. y in the preparation of glucose and chlorides. y for bleaching in textile industry. y to clean metals before they are tinned, soldered or

galvanised.

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Know this :Galvanisation is the process of coating iron or steel with zinc either by immersing in a bath of molten zinc or by deposition from a solution of zinc sulphate. This is done to avoid corrosion.

2. Nitric acid (HNO3) is used : y to etch designs or names on metals

Fig. 8.8 Etching design on

a metal vessel

like copper, brass and bronze.

y in the purification of precious metals like gold and silver.

y to extract metals from their ores.

y in the manufacture of some dyes, perfumes, plastics, rayon (artificial silk), fertilizers (like ammonium nitrate), explosives (like TNT- trinitro toluene and nitro glycerine) and medicines.

Know this :An ore is a naturally occurring mineral that yields metals or valuable minerals.

3. sulphuric acid (H2sO4) is used : y to refine petrol.

y in the manufacture of Know this :

Sulphuric acid is called the King of acids as it has so many uses.

f e r t i l i z e r s ( a m m o n i u m sulphate, superphosphate), detergents, drugs, plastics,

paint and chemicals (copper sulphate, epsom salt.)

y in paper, leather, textile and automobile industries.

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Know this :Epsom salt is magnesium sulphate (MgSO4. 7H2O) It is a naturally occurring mineral in water. Its name is derived from the town of Epsom, England where the compound was first distilled.

4. carbonic acid (H2cO3) is used : y in the preparation of aerated soft drinks.

5. Aqua Regia is used : y in etching designs on metals like gold and platinum.

Know this :Aqua Regia is a mixture of concentrated hydrochloric acid and concentrated nitric acid in the ratio 3 :1. This mixture dissolves noble metals like gold and platinum.

bases :Have you tasted a bitter gourd?

Fig. 8.9 Bitter guard

What does it taste like? Obviously it is bitter as its name suggests. This bitterness is due to a chemical compound in it. Chemical compounds that are bitter to taste are called bases.

Just like how acids have a hydrogen part, bases have a hydroxyl (OH) part. A base is made up of one or more hydroxyl (OH) groups attached to a metal.

base Metal part Hydroxyl group

Na OH Na+ (OH -)

Ca OH2 Ca++ 2(OH-)

When bases dissolve in water they split up into the metal part and the hydroxyl group as shown in the above table.

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Know this :The oxides and hydroxides of metals are bases.

Do all bases dissolve in water? No, all bases do not dissolve in water. The bases that dissolve in water generate hydroxyl ion [(OH)-] and are called alkalis.

Know this :All alkalis are bases but all bases are not alkalis.

Bases that dissolve in water are alkalis.

Bases that do not dissolve in water are non-alkalis.

� Sodium hydroxide.

� Potassium hydroxide.

� Aluminium hydroxide.

� Copper hydroxide.

Properties of bases :

Physical properties of bases :

1. Taste : Bases are bitter to taste.

2. Feel : Bases are soapy to touch.

3. conductivity : Solutions of bases are good conductors of electricity.

4. corrosiveness : Some bases are corrosive in nature.

Know this :NaOH is the most corrosive base. Carbonic acid is the least corrosive acid.

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5. litmus effect : Activity 8.4 : Dip a red litmus paper in a solution of sodium hydroxide solution. What do you observe? Bases turn red litmus paper blue.

Fig. 8.10 Red litmus paper with a drop of a base

Activity 8.5 : Make your own litmus

Fig. 8.11 Red cabbage

paper at home. Boil some pieces of red cabbage in a vessel of water. Cool and strain out the coloured water. Cut strips of blotting paper and dip them into this coloured solution. Remove and place them on a plastic sheet to dry. Your home made litmus paper is ready.

chemical properties :

Bases react with acids to form salt and water. For example, when the base, calcium hydroxide reacts with sulphuric acid, the salt calcium sulphate and water are formed. � Calcium hydroxide + Sulphuric acid → Calcium sulphate

(salt) + Water.

� Sodium hydroxide + Hydrochloric acid → Sodium chloride (salt) + Water.

Indicators :

Indicators are chemical substances to indicate if a substance is acidic, basic or neutral (neither acidic nor basic).

The most commonly used indicator is litmus. Turmeric and red cabbage are natural indicators. The other indicaters used in a laboratory are methyl orange and phenolphthalein.

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The following table gives the change in colour when different indicators are added to acids and alkalis.

sl. No. Indicator colour in acids

colour in alkalis

1. Red- Cabbage (purple) red green

2. Turmeric water (yellow)

no change in colour reddish brown

3. Blue litmus red _____

4. Red litmus _____ blue

5. Methyl orange red yellow

6. Phenolphthalein colourless pink

Uses of bases :

The most commonly used bases are sodium hydroxide, calcium hydroxide and ammonium hydroxide.

1. sodium hydroxide (NaOH) (caustic soda) is used : y in textile, plastic and soap industries. y to refine petroleum. y in the manufacture of rayon, medicine and paper.

2. calcium hydroxide [ca(OH)2] (slaked lime) is used : y in white washing. y as an antidote for acid poisoning. y in the manufacture of bleaching powder, cement, mortar

and fungicides.

y for removing fur from animal skin.

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3. Ammonium hydroxide [NH4(OH)] is used : y to remove ink from clothes and grease stains.

y in the manufacture of fertilizers like ammonium nitrate, dyes, plastics and nylon.

Know this :Ammonium hydroxide is the only base that does not have a metal atom. Instead it has a (NH4)

+ radical in it.

Neutralization :

experiment :

Take about 10ml of sodium hydroxide solution in a conical flask. Using a dropper add a few drops of phenolphthalein and stir. What is the colour of the solution? It becomes pink in colour as sodium hydroxide is an alkali.

vv

white tile

conical flask

sodium hydroxide and

phenolphthalein

sulphuric acid

burette burette

Fig. 8.12 Neutralization reaction

Now add a few drops of dilute sulphuric acid using a burette and shake the flask. What do you observe?

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As dilute sulphuric acid is added, the pink colour of the solution fades. On adding more drops of dilute sulphuric acid, the pink colour disappears, making the solution colourless. What does this indicate? The solution is now acidic in nature.

Now add a drop of sodium hydroxide solution and stir. The solution becomes pink again. Add a drop of dilute sulphuric acid. What happens? The solution becomes colourless.

The reaction of a base with an acid to form the respective salt and water is called neutralisation reaction. The resulting solution is called the neutralised solution.

A neutralised solution is so called as the acidic and basic nature of the solution is cancelled out producing a neutral solution.

Applications of neutralisation :

The process of neutralisation is so very useful in day-to-day life.

Bee stings are acidic. An application of baking powder (sodium bicarbonate), a base on the sting area helps to neutralise and hence ease the pain and burning sensation on the skin.

Our stomach contains traces of dilute hydrochloric acid which is required for the digestion of food. The formation of too much of acid in the stomach due to unhealthy eating or not eating on time can cause discomfort and damage the inner layer of the stomach. This can be eased by taking antacids (which are bases) that help to neutralise the stomach.

Farmers mix lime (calcium oxide) to the soil which is acidic to neutralise the soil to make it fit to grow plants. Plants cannot grow well in soil which is too acidic or too basic in nature.

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Acids and bases - a comparison :

Property Acids bases.

Taste sour bitter

Feel irritates/ burns skin. soapy to touch

Action with litmus paper

turns blue litmus red.

Turns red litmus blue.

Corrosiveness corrosive some are corrosive.

Conductivity conducts electricity

conducts electricity.

Action with each other

reacts with bases forming salts and water

reacts with acids forming salts and water.

salts :

You already know that salts are prepared by the neutralisation reaction of acids and bases. You also know that salts can be formed by the reaction of acids with metals, metal oxides, metal carbonates and metal bicarbonates.

Properties of salts :

The general properties of salts are :

1. Most salts are solids with high melting and boiling point.

2. Most salts are soluble in water.

3. Salts soluble in water make the solution a good conductor of electricity.

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Uses of important salts :1. sodium chloride (common salt) is : y required in small quantities by the human body and adds

taste to our food. y very essential in pickling and curing of fish and meat. y used in pottery glazing. y necessary in the manufacture of chlorine, hydrochloric

acid, sodium carbonate, sodium hydroxide and sodium bicarbonate.

2. sodium carbonate (Na2cO3) (washing soda) is used : y to wash clothes y to refine petroleum y in the manufacture of caustic soda, borax, detergents,

paper and glass.3. sodium bicarbonate ( NaHcO3) (baking soda) is used : y in bakery products like bread and cakes

Fig. 8.13 Fire extinguisher

y as an antacid y in fire extinguishers.

4. copper sulphate (cusO4) (blue vitriol) is used : y to manufacture medicines. y as a fungicide.

y for electroplating, making dyes and in calico printing.

5. Potassium nitrate (KNO3) is used : y in glass, fertilizer and refrigeration industries y manufacture of gun powder.

6. Potash Alum [KAl(sO4)2] is used : y in the purification of water and in the tanning industry.

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Know this :Tanning is a process of making leather from the skin of animals.

7. silver nitrate (AgNO3) is used : y in developing films. Today it is not in much use as we have

digital photography.

pH Value :

Is it possible to measure the acidity or basic strength of substances? It can be measured using a special scale called the pH scale.

neutralbase

milk of magnesiamilk

watercabbagelemon juice

hydrochloric acid

acid

Fig. 8.14 : pH scale

Know this :

pH is the measure of concentration of hydrogen ionand it indicates acidity or alkalinity of a solution.

If the value on a pH scale is zero to less than seven (i.e 0,1,2,3,4,5,6 and not 7) the substance is acidic in nature.

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If the value on a pH scale is greater than seven upto fourteen (i.e 8,9,10,11,12,13,14) the substance is a base.

What happens if the pH scale indicates seven ? A pH value of seven indicates that the given solution is neither an acid nor a base. It is neutral.

Importance of pH in our daily life :

The pH range within which the human body functions is 7 to 7.8. The human stomach produces hydrochloric acid (1.5 to 4 pH ) to help digestion. An increase in this acid can be managed by taking an antacid (a mild base) to neutralise the excess acid.

saliva 6.5 - 7.5 pH

upper stomach (fundie) 4.0 - 6.5 pH

lower stomach 1.5 - 4.0 pHduodenum 7.0 - 8.5 pHsmall intestine 4.0 - 7.0 pH

large intestine 4.0 - 7.0 pH

Fig. 8.15 Human digestive tract pH range chart

The pH range in the mouth should be around 6.5 to 7.5. If the pH value falls below 6.5, the acidity increases causing tooth decay. This could be prevented by cleaning the teeth with tooth paste which is basic.

The pH of soil plays a great role in the growth of plants.

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Remember

� Chemical compounds are classified into acids, bases and salts.

� Acids can be classified as organic acids and mineral acids (inorganic acids).

� Acids that occur in nature are called organic acids.

� Mineral acids are prepared from minerals obtained from the earth.

� When acids dissolve in water it splits up into its hydrogen part and radical part.

� An acid is a compound which when dissolved in water gives only hydrogen ions as the positive ion.

� Acids are sour to taste, corrosive.

� Acid in water makes the solution conductive.

� Acids turn blue litmus red.

� Acids react with metals to form the respective salts and liberate hydrogen.

� Acids react with metal carbonates and bicarbonates to form salts, carbondioxide and water.

� Hydrochloric acid is used to manufacture glue, purify common salt, to prepare glucose and chlorides. It is also used in the textile industry and in cleaning metals before tinning, soldering or galvanising.

� Nitric acid is used to etch designs on copper, brass or bronze vessels and in the purification of precious metals. It is used to extract metals from their ores and manufacture some dyes, perfumes, plastics, rayon, fertilizers, explosives and medicines.

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� Sulphuric acid is used to refine petrol, manufacture fertilizers, detergents, drugs, plastics, paint and chemicals. It is also used in the paper, leather, textile and automobile industries.

� Carbonic acid is used in the preparation of soft drinks.

� Aqua Regia is used in etching designs on precious metals.

� Bases when dissolved in water give rise to a metal part and a hydroxyl group.

� Bases are bitter to taste.

� Bases are soapy to touch.

� Solutions of bases in water are good conductors of electricity.

� Some bases are corrosive.

� Bases turn red litmus blue.

� Bases react with acids to form salt and water.

� An indicator is a chemical substance to indicate if a substance is acidic, basic or neutral. Turmeric and red cabbage are natural indicators.

� Litmus paper, methyl orange and phenolphthalein are other commonly used indicators.

� Sodium hydroxide (caustic soda) is used in textile, plastic and soap industries, in refining petroleum and in the manufacture of rayon, medicine and paper.

� Calcium hydroxide (slaked lime) is used in white washing, in the manufacture of bleaching powder, cement and fungicides. It is also used as an antidote for acid poisoning and removing fur from animal skin.

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� Ammonium hydroxide is used to remove ink and grease stains from clothes. It is also used in the manufacture of fertilizers, dyes, plastics and nylon.

� A neutralised solution is a solution which is neither acidic nor basic in nature.

� Salts are formed by neutralising reaction or by the reaction of acids with metals, metal oxides, metal carbonates or metal bicarbonates.

� Most salts are solids with high melting and boiling point. They dissolve in water making the solution a good conductor of electricity.

� Sodium chloride is essential for the human body. It is used in pickling and curing of fish and meat.

� Washing soda is used in washing clothes and refining petroleum.

� Baking soda is used in making bakery products.

� Copper sulphate is used in the manufacture of medicines and as a fungicide.

� Potassium nitrate is used in glass, fertilizer and refrigeration industries.

� Potash Alum is used in the purification of water.

� Silver nitrate is used in developing films.

� A scale called the pH scale is used to measure the acidity or basicity of substances.

� A value zero to less than seven on the pH scale indicates an acidic substance.

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� A value greater than seven to fourteen on the pH scale indicates a base.

� Exactly seven on the pH scale denotes a neutral solution or substance.

� An increase in acidity in the stomach causes discomfort.

� An increase in acidity in the mouth can cause tooth decay.

Tips y Avoid eating junk food which affects the digestion in our

body. y Develop good eating habits. Eat like a king in the morning. y Eat vitamin C rich fruits and vegetables which strengthens

your immune system.

exercises

I. Four alternatives are given under each complete/ incomplete statement. choose the correct answer and put a tick () mark against it :

1. The one which is not an organic acida) lactic acid b) acetic acidc) carbonic acid d) citric acid

2. Hydrochloric acid is used in a) purifying precious metals like goldb) refining petrolc) purifying common saltd) preparing soft drinks

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3. Caustic soda is not used in this industry a) textile b) rayonc) soap d) cement

4. The chemical used by farmers to neutralise acid content in the soil isa) calcium oxide b) calcium hydroxidec) calcium carbonate d) calcium chloride

II. Fill in the blanks with suitable words :1. Vitamin C is chemically called ___________ acid.

2. Mineral acids are also called ___________ acids.

3. Bases that dissolve in water are called ___________.

III. Write the chemical names for the following :

1. common salt 2. caustic soda 3. washing soda

4. slaked lime 5. baking soda 6. epsom salt.

IV. Match the following organic acids given in list ‘A’ with the food items given in list ‘b’ :

A b1. lactic acid a) lettuce leaves2. folic acid b) apple3. tannic acid c) unripe mango4. tartaric acid d) tomato5. malic acid e) tea f) vinegar g) milk

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V. Answer the following questions :

1. What are organic acids?

2. Make a list of four physical properties of

a) acids

b) bases

3. What are indicators? Give two examples.

4. What is a neutralisation reaction?

5. Mention two applications of neutralisation reaction?

6. What is pH value? If the pH value of a substance is 13, what does it indicate?

7. A solution indicates seven on the pH scale, what does this tell you about the solution?

8. Write two uses of each of the following :

a) hydrochloric acid

b) sulphuric acid

c) caustic soda

d) slaked lime

e) sodium chloride

f) baking soda

g) washing soda

9. Hydrogen is liberated when acids react with metals. Explain this with the help of an experiment.

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10. Explain the reaction of an acid with calcium carbonate with the help of a diagram.

11. Write an experiment to show the neutralisation of a base with an acid.

12. Make a list of four differences between the properties of acids and bases.

13. What is the importance of pH value in daily life.

VI. What happens when :

1. a blue litmus paper is dipped in lime juice?

2. potassium reacts with sulphuric acid?

3. calcium reacts with sulphuric acid?

4. mangnesium carbonate reacts with sulphuric acid?

5. a base reacts with an acid.

VII. Give reasons for the following :

1. A person bitten by red ants experiences a burning sensation on the skin.

2. A drop of concentrated sulphuric acid on a piece of cloth creates a hole in it.

3. Acids are not stored in metal containers.

4. All alkalis are bases but all bases are not alkalis.

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unit - 9atom

after studying this unit you : � define the term atom. � make a list of the assumptions made by John Dalton. � make a list of the sub atomic or fundamental particles

of an atom. � recognise the position of the fundamental particles of an

atom. � compare the basic properties of fundamental particles of

an atom. � explain the structure of hydrogen atom. � define terms like atomic number and mass number. � identify the shells in an atomic structure. � calculate the maximum number of electrons a shell can

contain. � define electronic configuration. � draw the atomic structure of the first twelve elements.

The ancient Indian philosopher Maharishi Kanada postulated that if matter is broken up, smaller and smaller particles of the same are obtained. As we do so, a stage will be reached where it cannot be further broken up or divided. Greek Philosophers like Laccippus and Democritus named it atom meaning indivisible. These concepts were abstract and were not based on experiments.

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John Dalton, a British Chemist, accepted this philosophy. After a series of experiments, he proposed his atomic theory called Dalton’s atomic theory.

Dalton’s atomic theory was based on the laws of chemical combination.

Know this :There are two laws of chemical combination. y Matter can neither be created nor destroyed in a chemical

reaction. y In a chemical substance, the elements are in definite

proportions.

Know this :

Fig 9.1 John Dalton

John Dalton was British scientist. At the young age of twelve, he assisted his elder brother in running his school. His most influential work in chemistry was his atomic theory proposed in 1808. This became one of the foundations of chemistry. He also conducted studies on colour blindness and called it Daltonism.

Dalton’s atomic theory :

John Dalton put forth his atomic theory in 1808. The postulates or assumptions made by him were as follows. � All matter is made up of small indivisible particles called

atoms. � Atoms can neither be created nor be destroyed. � There are many kinds of atoms as there are elements. � Atoms of a given element are identical in mass and chemical

properties.

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� Atoms of different elements have different masses and chemical properties.

� It is the atom in an element that takes part in a chemical reaction.

� Atoms of different elements combine in simple integral ratios to form compounds.

� Atoms of different elements can be hold apart by their atomic weight.

Know this :Atomic mass is the mass of an atom expressed in atomic mass units (amu). One amu also called as dalton, equals

121 th the weight of an atom of carbon 12.

Dalton’s atomic theory and the idea of the indivisibility of the atom was accepted for many years. Later scientists like William Crookes (1878), J. J. Thomson (1879) and Goldstein (1866) brought out theories against that of Dalton’s.

Some of John Dalton’s assumptions about atoms were not precise. It was modified and today we call it the modern atomic theory.

Fundamental particles of an atom :

Just as cells are the basic unit of organisms, atoms are the basic unit of matter. It is clearly understood that an atom can be further divided into smaller particles called sub - atomic particles.

Sub - atomic particles :

The sub - atomic particles of an atom are electrons, protons and neutrons. These particles are present in almost all atoms. The actual number of sub - atomic particles may vary from element to element and is always a whole number.

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Now you may be curious to know where in an atom are these sub atomic particles.

Position of Sub - atomic particles :

All atoms have a specific region in them called the nucleus. Protons and neutrons are situated in the nucleus of an atom and hence are called nucleons. Then where are the electrons?

nucleuselectron

protonneutron

Fig. 9.2 : Sub-atomic particles in an atom

Just as the planets revolve around the sun in fixed orbits, the electrons of an atom move around its nucleus along fixed paths called orbits.

Know this :J.J. Thomson discovered the electron, Goldstein discovered the proton and James Chadwick discovered the neutron.

Characteristics of electrons : � Electrons are negatively charged particles found in all

atoms. � The mass of an electron is about 1840

1 of the relative mass of hydrogen atom.

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Know this :

Fig 9.3 Sir J.J. Thomson

Sir Joseph John Thomson was a British Physicist. He discovered the electron and was awarded the Nobel Prize in physics for this discovery in 1906. He was also the first scientist to separate isotopes of chemical elements. His model of the atom was not accepted after new models were proposed by Ernest Rutherford in 1911 and Niels Bohr in 1913.

Characteristics of protons :

� Protons are positively charged particles found in all atoms.

� The relative mass of a proton is 1 amu.

Know this :

The relative mass of the atom of an element is defined as the average mass of the atom, as compared to 12

1 th the mass of one carbon -12 atom.

Characteristics of neutrons :

� Neutrons do not have charge and hence are neutral particles.

� The relative mass of a neutron is the same as that of a proton i.e. 1 amu.

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Know this :

Fig. 9.4Sir J. Chadwick

Sir James Chadwick was a British Physicist. In 1935, he received the Nobel Prize in Physics for the discovery of the neutron. He also determined the mass of a neutron.

Let us now sum up the position, relative charge and relative mass of the sub atomic particles.

Sub - atomic particle Position Relative

chargeRelative mass

(amu)

Electronoutside the nucleus, in specific orbits

Negative 18401 of

hydrogen atom

Proton in the nucleus Positive 1

Neutron in the nucleuszero

(no charge)1

You already know that neutrons are sub atomic particles present in all atoms, except hydrogen. Now let us study the structure of the hydrogen atom.

Structure of Hydrogen atom :

The symbol used to represent a hydrogen atom is H. The term hydrogen comes from the greek word meaning water former. It is the lightest and simplest known atom.

Sir Henry Cavendish discovered hydrogen and identified it as an element in 1766. Livoisier named it hydrogen.

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Know this :

Fig. 9.5 Sir Henry Cavendish

Sir Henry Cavendish was a British physicist and chemist. In 1766 he discovered the properties of hydrogen, identified it as an element and called it inflammable air. Later he also showed that water was a compound of hydrogen and oxygen. His work on electricity resulted in many fundamental laws.

In the structure of the hydrogen atom

proton

nucleuselectron

Fig. 9.6 Hydrogen atom

we see that the nucleus contains one proton. An electron orbits the nucleus.

The number of protons in an atom of an element is unique to that particular element and this number is called its atomic number. As hydrogen has one proton, its atomic number is one.

Every atom of an element has a unique number called mass number. The mass number of an atom is the total number of protons and neutrons in the nucleus of that atom. As hydrogen has one proton and no neutrons, its mass number is one.

Shells of an atom :

T h e o r b i t s a r o u n d

321882

KLMN

nucleus

Fig. 9.7 Electronic shells of an atom

the nucleus of an atom are called shells. In these shells electrons revolve round the nucles in different orbitals . The shells are named as K, L, M, N etc.

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K - Shell :

The shell closest to the nucleus is the K - Shell or first shell. It can contain a maximum number of 2 electrons.

L - Shell :

The shell next to the K - Shell is the L - Shell or the second shell. It can contain a maximum number of 8 electrons.

m - Shell :

The shell next to the L - Shell is the M - Shell or the third shell. It can contain a maximum number of 18 electrons.

n - Shell :

The shell next to the M - Shell is the N - Shell or the fourth shell. It can contain a maximum of 32 electrons.

maximum number of electrons in a shell :

How is the maximum number of electrons in a particular shell calculated? It is calculated using the formula 2n2 where n is the shell number. For the K - Shell n =1, for the L - Shell n = 2 and so on.

Calculate the maximum number of electrons in each shell.

name of shell n 2n2 maximum number of electrons

K 1 2 × 12 = 2 2L 2 2 × 22 = 8 8

M ______ __________ _____________

N ______ __________ _____________O ______ __________ _____________

P ______ __________ _____________

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Electronic configuration :

The distribution of electrons in various shells of an atom is called its electronic configuration. Look at the following table to understand the atomic structure and electronic configuration of the first twelve elements.

Element Symbol atomic structure

Eletronic configuration

K L m n

Hydrogen H 1

Helium He 2

Lithium Li 2 1

Beryllium Be 2 2

Boron B 2 3

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Carbon C 2 4

Nitrogen N 2 5

Oxygen O 2 6

Fluorine F 2 7

Neon Ne 2 8

Sodium Na 2 8 1

Magnesium Mg 2 8 2

Fig. 9.8 : Atomic structure and electronic configuration of elements.

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Remember

� The Dalton’s atomic theory was put forth in 1808 by John Dalton.

� Electrons, protons and neutrons are the sub atomic particles of an atom.

� Protons and neutrons are in the nucleus of an atom.

� Electrons orbit around the nucleus of an atom.

� Electrons are negatively charged particles. Its mass is about 1840

1 of the relative mass of the hydrogen atom.

� Protons are positively charged particles. Its relative mass is 1 amu.

� Neutrons are neutral.(Neither negative nor positive)

� Atoms of all elements except hydrogen have neutrons.

� The relative mass of a neutron is 1 amu.

� James Chadwick discovered the neutron.

� Hydrogen is the lightest and simplest known atom.

� Sir Henry Cavendish discovered hydrogen.

� The number of protons in an atom represents its atomic number.

� The total number of protons and neutrons of an atom is called mass number.

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� The orbits of an atom are called its shells. The K- Shell contains a maximum of 2 electrons, the L - shell 8, the M - shell 18 and the N - Shell 32 electrons.

� The formula to calculate the maximum number of electrons in a shell of an atom is 2n2, where n = 1,2,3,4,5.

Exercises

i. Four alternatives are given under each complete/ incomplete statement. Choose the correct answer and put a tick () mark against it :

1. The maximum number of electrons that the N - Shell can hold is

a) 12 b) 18

c) 2 d) 32

2. The scientist who named electrons is

a) J. J. Thomson b) John Dalton

c) Kanada d) James Chadwick

3. The scientist who discovered the neutron is

a) Ernest Rutherford b) J. J. Thomson

c) James Chadwick d) John Dalton

4. The sub - atomic particles in the nucleus is

a) electrons and orbit b) electrons and neutrons

c) neutrons and protons d) protons and electrons

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5. The maximum number of electrons in the M shell is

a) 2 b) 18

c) 50 d) 32

6. The symbol for hydrogen atom is

a) He b) H2

c) Hg d) H

ii. Fill in the blanks with suitable words :

1. The basic unit of an element is ____________.

2. The smaller particles in an atom are called ____________ .

3. The charge of an electron is ____________.

4. The relative mass of a proton is ____________ amu.

iii. match the elements given in list ‘a’ with their electronic configurations given in list ‘B’ :

A B

1. Hydrogen a) 2

2. Nitrogen b) 2, 8, 2

3. Lithium c) 2, 8

4. Neon d) 2, 5

5. Magnesium e) 1

f) 2, 1

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iV. answer the following questions :

1. What is atomic number?

2. What is 1 amu?

3. Explain sub-atomic particles.

4. What is mass number?

5. What is electronic configuration?

6. What are the characteristics of

a) electrons

b) protons

c) neutrons

7. Make a list of any four postulates of Dalton’s atomic theory.

8. Neutrons are called neutral particles. Why?

Project work

� Make a model showing the atomic structure of an element.

� Prepare a chart showing the symbols and electronic configuration of the first twenty elements.

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UNIT - 10HARD WATER AND SOFT WATER

After studying this unit you : � recall the meaning of hard water. � define the term hard water. � make a list of the salts present in hard water. � make a list of the disadvantages of hard water. � define the term soft water. � conduct simple experiments to soften hard water. � appreciate the uses of soft water. � differentiate between hard and soft water. � recognise the different types of hydrogen atoms. � define the term heavy water. � recognise the physical properties of heavy water. � mention the uses of heavy water. � state the disadvantages of heavy water.

You know that the surface of the earth has many water bodies. The largest sources of water are the seas and oceans. Do you think that all this water is usable by man? No. Do you know why?

Know this :22 nd March is celebrated as world water day.

Have you ever tried to dissolve the substances such as sugar, jaggery and salt in water ? Do they dissolve? Most of the substances dissolve in water. Why? This is because water is a universal solvent.

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Let us find out what happens to water when materials or chemicals dissolve in it.Experiment :

Take equal quantities of distilled water in five test tubes namely A, B, C, D and E. Dissolve chlorides of sodium, potassium, ammonium, calcium and magnesium in each test tube respectively.

Pour a small quantity of soap solution into each test tube and shake the test tubes well. What do you observe?

A B C D E

sodium chloride potassium

chloride

ammonium chloride calcium

chloride

magnesium chloride

Fig. 10.1 : Water samplesThe test tubes A, B and C produce lather with soap

solution the test tubes D and E do not produce lather with the soap solution.

What do you conclude from this ? Calcium and magnesium salts in water prevent soap solution from lathering.Hard water :

Water is termed hard water if it contains dissolved salts of chlorides, sulphates and bicarbonates of calcium and magnesium.

Example : water of some wells, sea water etc.

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Soft water :

Water that is free from calcium and magnesium salts that cause hardness of water is called soft water. Examples : Rain water and distilled water.

Know this :Hard water could contain one of these compounds. Calcium chloride, calcium sulphate, calcium bicarbonate, magnesium chloride, magnesium sulphate and magnesium bicarbonate.

Areas that have hard water face some difficulties.Disadvantages of hard water :

Have you observed that water from all sources do not produce lather with soap? Do you know why?

When clothes are washed in hard water the magnesium ions (Mg++) and the calcium ions (Ca++) present in hard water, react with soap to form scum, which is insoluble in water. This results in wastage of soap. Moreover the clothes do not become clean.

Most industries need super heated steam for different processes carried out by them. To produce this super heated steam, water is boiled in huge boilers and passed through pipes.

If hard water containing calcium bicarbonate is used for this purpose, the calcium bicarbonate decomposes to insoluble calcium carbonate.

Calcium bicarbonate boiling

Calcium carbonate + Carbon dioxide + Water.

The calcium carbonate thus formed deposits at the bottom of the boiler and the walls of pipes. This deposit is stone like and is called scaling.

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Fig. 10.2 : Scaling in pipes

The deposit of calcium carbonate in the boiler is a bad conductor of heat. As more and more hard water is boiled more deposit is formed. When water is further heated, it is noticed that it takes more time for the water to boil. The deposited layer of calcium carbonate could develop cracks and pressure could increase inside the boiler. This could lead to a dangerous boiler blast. Hence hard water is neither economical nor safe to be used in industries.

When utensils are washed in hard water, they tend to lose their luster. These utensils generally have a dull, dirty look.

Types of hard water :Hard water is of two types they are, temporary hard water

and permanent hard water.

1. Temporary hard water :Temporary hardness of water is caused due to the dissolved

bicarbonate of calcium and magnesium. It can be removed by the process of boiling. The bicarbonates decompose to carbonates. The carbonates can be filtered out.

2. Permanent hard water :Permanent hardness is caused due to the dissolved

chlorides and sulphates of calcium and magnesium. It can be removed by adding sodium carbonate or by passing permanent hard water through zeolite.

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Hard water needs to be softened as it has some disadvantages. Depending on the salts dissolved in water, different methods can be administered to soften hard water.

Methods to soften hard water :1. Boiling :

Hard water has to be boiled and filtered to remove hardness.

2. Adding sodium carbonate (washing soda) :

Activity 10.1 : Take 20 ml of hard water in a beaker. Add a spoon of sodium carbonate to it. What do you observe? An insoluble precipitate is formed. This precipitate is either calcium carbonate or magnesium carbonate depending on the salt present in the hard water sample taken. Remove the precipitate by filtration. The water, so obtained is soft. To further test this water, pour some soap solution in it and shake well. Does it lather? Yes,it does, showing that the water is soft.

3. Ion exchange process :

Permanent hardness isinlet for hard water

brine solution

outlet for soft water

soft water

permutit

coarse sand and gravel

other uses

Fig. 10.3 : Ion exchange process

due to the dissolved salts of chlorides and sulphates of calcium and magnesium. This type of hardness can be removed by the process of ion exchange.

Hard water is passed through a mixture called zeolite to obtain soft water.

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Zeolite is a mixture of sodium, aluminium and silicates. When hard water is passed though this mixture, the calcium ions and the magnesium ions of hard water are replaced by the sodium ions of the mixture making the water soft. Zeolite is widely used in domestic and commercial water purification.

Know this :An example of zeolite is natrolite Na2Al2Si3O10. 2H2O. Synthetic zeolite is called permutit and hence this process is also called permutit process.

Uses of soft water :

1. By using soft water to wash cloths we can minimise the use of soap and cloths will be cleaned better.

2. The life span of appliances are prolonged when soft water is used.

3. Soft water helps to improve digestion.

Differences between hard water and soft water :

Hard water Soft water1. Hard water does not

lather with soap easily.1. Soft water lathers easily

with soap.2. It contains dissolved

salts of calcium and magnesium.

2. It does not contain dissolved salts of calcium and magnesium.

avÀæ 10.4 : ªÉÄzÀÄ ¤ÃgÀÄ ¸Á§Æ¤£ÉÆA¢UÉ £ÉÆgÉ PÉÆqÀÄvÀÛzÉ.

Fig. 10.4 : Soft water lathers with soap

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Types of hydrogen atom :You are familiar with the electron

nucleus showing one proton

Fig. 10.5 Structure of hydrogen atom

structure of the hydrogen atom. There are three types of hydrogen atoms. What is the difference between these atoms?

A hydrogen atom with one proton and one electron is called protium.

A Hydrogen atom with a proton, a neutron and an electron is called deuterium.

A Hydrogen atom with a proton, two neutrons and an electron is called tritium.

Know this :Elements that have the same number of protons and different number of neutrons are called isotopes.

Heavy water :Deuterium reacts with oxygen to form a compound called

deuterium oxide (D2O). This is called heavy water.

Know this : The American chemist Herold.C.Urey

Fig. 10.6 Herold.C.Urey

discovered deuterium. He won the Nobel Prize in chemistry for this discovery in 1934. He isolated deuterium, the stable isotope of hydrogen by repeatedly distilling a sample of liquid hydrogen. Harold.C.Urey had a significant role in developing the atom bomb, but his theories on the development of organic life from non - living matter made him known in the scientific field.

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Physical properties of heavy water :

The physical properties of heavy water are very different from that of water, because of the differences in the atomic masses of hydrogen and deuterium.

Know this :The atomic mass of hydrogen is 1.0079 amu and that of deuterium is 2.014 amu. (amu - atomic mass unit)

Heavy water is about 10% heavier than normal water. This is due to the extra neutron in deuterium.

The following table gives a comparison of the physical properties of water and heavy water.

Water Heavy water

1. Freezes at 0 oC 1. Freezes at 3.82 o C

2. Boils at 100 oC 2. Boils at 101.42 oC

3. Ice floats 3. Ice sinks

Uses of heavy water :

Heavy water is used to prepare deuterium and in nuclear reactors. You will study about the nuclear reactor in higher classes.

Disadvantages of heavy water :

Though water is very essential to us, heavy water has some disadvantages.

1. Heavy water is mildly toxic.

2. It is injurious to living organisms.

3. It is unfit for agriculture.

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Remember

� Water is a universal solvent.

� Hard water contains dissolved chlorides, sulphates and bicarbonates of calcium or magnesium.

� Water that is free from all calcium and magnesium salts that cause hardness of water is called soft water.

� Temporary hardness of water is caused due to the dissolved bicarbonates of calcium and magnesium.

� Permanent hardness of water is caused due to the dissolved chlorides and sulphates of calcium and magnesium.

� Hard water can be made soft by boiling, adding sodium carbonate or by the ion exchange process.

� Temporary hardness of water can be removed by boiling.

� Permanent hardness of water can be removed by adding sodium carbonate or by the ion exchange process.

� Soft water is more economical and efficient as it prolongs the life span of electrical appliances and it lathers readily with soap than hard water.

� A hydrogen atom with a proton and an electron is called protium.

� A hydrogen atom with a proton, a neutron and an electron is called deuterium.

� A hydrogen atom with a proton, two neutrons and an electron is called tritium.

� The oxide of deuterium is heavy water.

� Herold. C. Urey discovered deuterium.

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� Heavy water is about 10% heavier than normal water.

� Heavy water freezes at 3.82 oC and boils at 101.42 oC .

� Ice floats in water whereas it sinks in heavy water.

� Heavy water is used to prepare deuterium and in nuclear reactors.

� Heavy water is mildly toxic, injurious to living organisms and unfit for agriculture.

Tips

y Use soft water to wash clothes and utensils as it avoids the wastage of soap.

y Use water limitedly.

Exercises

I. Four alternatives are given under each complete/ incomplete statement. Choose the correct answer and put a tick () mark against it :

1. The chemical formula for calcium bicarbonate is

a) CaHCO3 b) Ca (HCO3)2c) CaH(CO3)2 d) Ca2(HCO3)2

2. Permanent hardness of water is due to the dissolved chlorides and sulphates of

a) Na and Mg b) Ca and Fe

c) Ca and Mg d) Na and Mn

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3. The number of protons, neutrons and electrons in deuterium is

a) 1,1,1 b) 1,0,2

c) 0,1,1 d) 1,2,3

II. Fill in the blanks with suitable words :

1. Temporary hardness of water is due to the dissolved bicarbonate of__________ and _________.

2. Water for commercial needs can be purified using __________.

3. Hydrogen has ___________protons and ___________ neutrons.

4. The temperature at which hard water freezes is __________.

5. Hard water boils at __________ 0C.

6. The total number of __________ and __________ in an atom is its mass number.

III. Underline the word which does not belong to the group :1. hydrogen, helium, tritium, deuterium.

2. calcium chloride, magnesium sulphate, carbon dioxide, calcium bicarbonate.

IV. Name the following :1. The isotope of hydrogen in heavy water.

2. The scientist who discovered deuterium.

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3. A method to remove temporary hardness of water.

4. A mixture of the oxides of sodium, aluminium sand and water.

V. Answer the following questions :1. Write the two disadvantage of hard water.

2. What is soft water?

3. Explain two methods of softening hard water.

4. What are the uses of soft water.

5. Differentiate between hard water and soft water.

6. Name the salts present in hard water.

7. What is the use of zeolite?

8. Describe an experiment to detect hardness and softness of water.

VI. What happens when :1. Hard water is used to wash clothes.

2. Ice is dropped into a beaker containing heavy water.

3. Utensils are constantly washed with hard water.

4. Washing soda is added to a beaker containing hard water.

VII. Give reasons for the following :1. It is dangerous to use hard water in industrial boilers.

2. Heavy water is unfit for agriculture.

3. The physical properties of heavy water are different from that of normal water.

RR

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