CHAPTER 1 Introduction to Chemistry

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1.2 Chemistry and Matter

Chemistry is the study of matter and the changes that it undergoes. Matter is anything that has mass and takes up space. Mass is a measurement of the amount of matter in an object. Everything, however, is not made of matter. For example, heat, light, radio waves, and magnetic fields are some things that are not made of matter.

You might wonder why scientists measure matter in terms of

mass, and not in terms of weight. Your body is made of matter, and

you probably weigh yourself in pounds. However, your weight is not

just a measure of the amount of matter in your body. Your weight

also includes the effect of Earth’s gravitational pull on your body.

This force is not the same everywhere on Earth. Scientists use mass

to measure matter instead of weight because they need to compare

measurements taken in different locations.

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Matter is made up of particles, called atoms, that are so small

they cannot be seen with an ordinary light microscope. The

structure, composition, and behavior of all matter can be explained

by atoms and the changes they undergo.

Because there are so many types of matter, there are many

areas of study in the field of chemistry. Chemistry is usually divided

into five branches, as summarized in the table below.

Branches of Chemistry

Branch Area of emphasis Examples

Organic chemistry

most carbon-containing

chemicals

pharmaceuticals,

plastics

Inorganic

chemistry

in general, matter that does

not contain carbon

minerals, metals and

nonmetals, semi-

conductors

Physical

chemistry

the behavior and changes

of matter and the related

energy changes

reaction rates, reaction

mechanisms

Analytical

chemistry

components and composition

of substances

food nutrients, quality

control

Biochemistry matter and processes of

living organisms

metabolism,

fermentation

1.3 Scientific Methods

A scientific method is a systematic approach used to answer a question or study a situation. It is both an organized way for scientists to do research and a way for scientists to verify the work of other scientists. A typical scientific method includes making observations, forming a hypothesis, performing an experiment, and arriving at a conclusion.

Scientific study usually begins with observations. Often, a

scientist will begin with qualitative data—information that describes

color, odor, shape, or some other physical characteristic that relates

to the five senses. Chemists also use quantitative data. This type of data

is numerical. It tells how much, how little, how big, or how fast.

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Practice Problems

1. Identify each of the following as an example of qualitative data or

quantitative data.

a. taste of an apple d. length of a rod

b. mass of a brick e. texture of a leaf

c. speed of a car f. weight of an elephant

A hypothesis is a possible explanation for what has been observed. Based on the observations of ozone thinning and CFC buildup in the

atmosphere, the chemists Mario Molina and F. Sherwood Rowland hypothesized that CFCs break down in the atmosphere due to the Sun’s ultraviolet rays. They further hypothesized that a chlorine particle produced by the breakdown of CFCs could break down ozone.

An experiment is a set of controlled observations that test a hypothesis. In an experiment, a scientist will set up and change one variable at a time. A variable is a quantity that can have more than one value. The variable that is changed in an experiment is called the independent variable. The variable that you watch to see how it changes as a result of your changes to the independent variable is called the dependent variable. For example, if you wanted to test the effect of fertilizer on plant growth, you would change the amount of fertilizer applied to the same kinds of plants. The amount of fertilizer applied would be the independent variable in this experiment. Plant growth would be the dependent variable. Many experiments also include a control, which is a standard for comparison; in this case, plants to which no fertilizer is applied.

A conclusion is a judgment based on the data obtained in the experiment. If data support a hypothesis, the hypothesis is tentatively affirmed. Hypotheses are never proven; they are always subject to additional research. If additional data do not support a hypothesis, the hypothesis is discarded or modified. Most hypotheses are not supported by data. Whether the hypothesis is supported or not, the data collected may still be useful. Over time, data from many experiments can be used to form a visual, verbal, and/or mathematical explanation—called a model—of the phenomenon being studied.

A theory is an explanation that has been supported by many experiments. Theories state broad principles of nature. Although theories are the best explanations of phenomena that scientists have at any given time, they are always subject to new experimental data and are modified to include new data.

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A scientific law describes a relationship in nature that is

supported by many experiments and for which no exception has

been found. Scientists may use models and theories to explain why

this relationship exists.

1.4 Scientific Research

Pure research is done to gain knowledge for the sake of knowledge itself. Molina and Rowland’s research on the behavior of CFCs—showing that in the lab CFCs could speed up the breakdown of ozone—was motivated by their curiosity and is an example of pure research. Applied research is undertaken to solve a specific problem. Scientists are conducting experiments to find chemicals to replace CFCs. These experiments are examples of applied research.

Laboratory safety During your study of chemistry, you will conduct experiments in the laboratory. When working in the lab, you are responsible for the safety of yourself and others working around you. Each time you enter the lab, use these safety rules as a guide.

Safety in the Laboratory

1. Study your lab assignment before you come to the lab. If you have any

questions, be sure to ask your teacher for help.

2. Do not perform experiments without your teacher’s permission. Never

work alone in the laboratory.

3. Use the table on the inside front cover of this textbook to understand

the safety symbols. Read all CAUTION statements.

4. Safety goggles and a laboratory apron must be worn whenever you are

in the lab. Gloves should be worn whenever you use chemicals that

cause irritations or can be absorbed through the skin. Long hair must be

tied back.

5. Do not wear contact lenses in the lab, even under goggles. Lenses can

absorb vapors and are difficult to remove in case of an emergency.

6. Avoid wearing loose, draping clothing and dangling jewelry. Bare feet

and sandals are not permitted in the lab.

7. Eating, drinking, and chewing gum are not allowed in the lab.

8. Know where to find and how to use the fire extinguisher, safety shower, fire blanket, and first-aid kit.

9. Report any accident, injury, incorrect procedure, or damaged

equipment to your teacher.

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Safety in the Laboratory, continued

10. If chemicals come in contact with your eyes or skin, flush the area

immediately with large quantities of water. Immediately inform

your teacher of the nature of the spill.

11. Handle all chemicals carefully. Check the labels of all bottles

before removing the contents. Read the label three times:

Before you pick up the container.

When the container is in your hand.

When you put the bottle back.

12. Do not take reagent bottles to your work area unless instructed to

do so. Use test tubes, paper, or beakers to obtain your chemicals.

Take only small amounts. It is easier to get more than to dispose

of excess.

13. Do not return unused chemicals to the stock bottle.

14. Do not insert droppers into reagent bottles. Pour a small amount

of the chemical into a beaker.

15. Never taste any chemicals. Never draw any chemicals into a

pipette with your mouth.

16. Keep combustible materials away from open flames.

17. Handle toxic and combustible gases only under the direction of

your teacher. Use the fume hood when such materials are present.

18. When heating a substance in a test tube, be careful not to point

the mouth of the test tube at another person or yourself. Never

look down the mouth of a test tube.

19. Do not heat graduated cylinders, burettes, or pipettes with a

laboratory burner.

20. Use caution and proper equipment when handling hot apparatus

or glassware. Hot glass looks the same as cool glass.

21. Dispose of broken glass, unused chemicals, and products of

reactions only as directed by your teacher.

22. Know the correct procedure for preparing acid solutions. Always

add the acid slowly to the water.

23. Keep the balance area clean. Never place chemicals directly on

the pan of a balance.

24. After completing an experiment, clean and put away your

equipment. Clean your work area. Make sure the gas and water

are turned off. Wash your hands with soap and water before you

leave the lab.

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Chapter 1 Review

2. How does the ozone layer protect Earth?

3. Why did scientists think that the thinning of the ozone layer might

be related to CFCs?

4. Contrast mass and weight.

5. During a chemistry lab, a student noted the following data

about an unknown chemical she was studying: colorless,

dissolves in water at room temperature, melts at 95°C, boils at

800°C. Classify each piece of data as either qualitative data or

quantitative data.

6. Identify the dependent variable and the independent variable in the

following experiments.

a. A student tests the ability of a given chemical to dissolve in

water at three different temperatures.

b. A farmer compares how his crops grow with and without

phosphorous fertilizers.

c. An environmentalist tests the acidity of water samples at five

different distances from a factory.

7. Explain why hypotheses and theories are always tentative

explanations.

8. List two possible hypotheses about the relationship between ozone

and CFCs.

9. Classify each kind of research as either pure or applied.

a. A scientist studies plants in a rain forest in search of

chemicals that might be used to treat AIDS.

b. A researcher studies the effects of hormones on the brain of

a worm.

c. A researcher tries to develop cleaner burning fuels to help reduce

air pollution.

10. State two rules you should follow when handling chemicals.

11. How should you dispose of the following items in the lab:

broken glass, products of chemical reactions, unused

chemicals?

Answer Key

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Chapter 1

Practice Problems

1. a. qualitative data d. quantitative data

b. quantitative data e. qualitative data

c. quantitative data f. quantitative data

Chapter 1 Review

2. The ozone layer protects plants and animals from overexposure to

ultraviolet radiation.

3. About the same time that the decrease in the ozone layer was

documented, scientists noticed that a large amount of CFCs had

accumulated in the atmosphere.

4. Mass is a measurement of the amount of matter in an object. Weight

is a measurement of an object’s mass plus the effect of Earth’s

gravitational pull on the object.

5. qualitative data: colorless, dissolves in water at room temperature;

quantitative data: melts at 95C, boils at 800C

6. a. independent variable: temperature; dependent variable: ability

to dissolve in water

b. independent variable: presence of phosphorous fertilizer;

dependent variable: crop growth

c. independent variable: distance from the factory; dependent

variable: acidity

7. Both hypotheses and theories are subject to revision based on new

data.

8. Accept any reasonable hypotheses. Molina and Rowland

hypothesized that CFCs break down in the atmosphere due to the

Sun’s ultraviolet radiation and that a chlorine particle produced by

the breakdown of CFCs could break down ozone.

9. a. applied b. pure c. applied

10. Answers should include any two of the rules listed in the Safety in

the Laboratory table that relate to the handling of chemicals (rules 4,

10–18, 22, and 23).

11. according to your teacher’s directions