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GCSE Chemistry 3 Summary Questions

and Answers

C3.1.1 The early Periodic Table (p73) Q1 Explain Newlands’ law of Octaves.

A1 - He arranged all the elements known at the time into a table in order of relative atomic mass.

- Newlands' table showed a repeating or periodic pattern of properties, but this pattern eventually broke down.

- By ordering strictly according to atomic mass, Newlands was forced to put some elements into groups which did not match their chemical properties.

Q2 Explain why Newlands’ law was criticised.

A2 - His groups contained elements that didn’t have similar properties. - Non-metals and metals were mixed. - He didn’t leave any gaps for elements that hadn’t been discovered yet.

Q3 Explain why Mendeleev was much more successful than Newlands.

A3 - He recognised that there were some elements still to be discovered, so he left gaps in his table.

- He was not afraid to change the order of some elements in the table where it seemed to make sense.

- He was able use the table to successfully predict the properties of some elements which had not yet been discovered.

C3.1.2 The modern Periodic Table (p74)

Q4 How are the elements in the Periodic Table arranged?

A4 - Elements in the Periodic Table are arranged in order of atomic number (number of protons in the nucleus).

- Elements in the Periodic Table are also arranged by their electronic structure.

Q5 How are the electrons in an atom set out?

A5 - Electrons in an atom are set out in shells which each correspond to an energy level.

Q6 What is the group number equal to?

A6 - The group number is equal to the number of electrons in their highest occupied energy level.

Q7 What is the period number?

A7 - The period number is the same as the number of occupied energy levels.

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C3.1.3 Trends within the Periodic Table (p75-p77)

Q8 As you go down Group 1, what is the trend in reactivity?

A8 - Elements become more reactive because the outer electron is more easily lost, since it is further away from the nucleus.

- Elements have lower melting and boiling points.

Q9 What properties do Group 1 elements have in common?

A9 The elements in Group 1 of the Periodic Table (known as the alkali metals): - are metals with low density (the first three elements in the group are less dense than

water). - react with non-metals to form ionic compounds in which the metal ion carries a charge

of +1.The compounds are white solids that dissolve in water to form colourless solutions.

- react with water, releasing hydrogen. - form hydroxides that dissolve in water to give alkaline solutions.

Q10 Explain why there is an increase in reactivity going down Group 1. [H]

A10 - This is because the atoms lower down have more inner shells of electrons. - These 'shield' the outer electrons from the attraction of the nucleus, and allow the outer

electron to be lost more easily. - Since metals react by losing electrons, they become more reactive.

Q11 As you go down Group 7, what is the trend in reactivity?

A11 - Elements become less reactive because it is more difficult to gain an extra electron, since the outer shell is further from the nucleus.

- Elements have higher melting and boiling points.

Q12 What properties do Group 7 elements have in common?

A12 The halogens have the following properties in common: - they are non-metals. - they have low melting and low boiling points. - they are brittle when solid. - they are poor conductors of heat and electricity. - they have coloured vapours. - their molecules are diatomic (each contain two atoms).

Q13 Explain why there is an decrease in reactivity going down Group 7. [H]

A13 - The electrons become less reactive as we go down the group because the outermost electron shell gets further away from the influence of the nucleus.

- Due to shielding, an electron is less easily gained.

Q14 What are halides?

A14 - The halogens form 1- ions called halides when they bond with metals.

Q15 The halogens are all non-metals with coloured vapours. Describe the colour of each of the following and state how reactive they are.

(a) Fluorine (b) Chlorine (c) Bromine (d) Iodine

A15 (a) Fluorine is a very reactive, poisonous yellow gas. (b) Chlorine is a fairly reactive, poisonous dense green gas. (c) Bromine is a dense, poisonous, red-brown volatile liquid. (d) Iodine is a dark grey crystalline solid or a purple vapour.

Q16 Fill in the blank: A more reactive halogen can ________ a less reactive halogen from an aqueous solution of its salt.

A16 - Displace.

Q17 Describe the properties of transition metals.

A17 - They’re good conductors of heat and electricity. - They are very dense, strong and shiny. - Transition metals are much less reactive than Group 1 metals and so do not react as

vigorously with Water or Oxygen. - Compared to Group 1 metals, they have higher melting points (except for Mercury) and

higher densities.

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Q18 What colours do the transition compounds have: (a) Potassium chromate (b) Potassium manganite (c) Copper (II) sulphate

A18 (a) Yellow. (b) Purple. (c) Blue.

Q19 Explain how Iron, Manganese oxide and Nickel are useful as catalysts.

A19 - Iron is the catalyst used in the Haber process for making Ammonia. - Manganese oxide is the catalyst used for the decomposition of Hydrogen peroxide. - Nickel is useful for turning oils into fats for making margarine.

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C3.2.1 Hard and soft water (p78 and p79)

Q20 What can soft water form?

A20 - Lather.

Q21 What can hard water form?

A21 - Scum. - Scale.

Q22 Which dissolved substances does hard water contain?

A22 - Calcium ions/ Ca2+. - Magnesium ions/ Mg2+.

Q23 What are the advantages of hard water?

A23 - Hard water is good for the development and maintenance of bones and teeth. - Hard water can help to lower the risk of heart disease. - Hard water can improve the taste of water.

Q24 What are the disadvantages of hard water?

A24 - More soap is needed to produce lather, which increases costs. This happens with temporary or permanent hardness.

- Temporary hardness can reduce the efficiency of kettles and heating systems. This is because limescale (a solid containing Calcium carbonate) is produced when the water is heated.

- The scum produced is unsightly - spoiling the appearance of baths and shower screens, for example.

Q25 What is the difference between temporary hard water and permanent hard water?

A25 Permanent hard water remains hard when it is boiled. Temporary hard water is softened by boiling.

Q26 What causes temporary hard water to be softened by boiling? Which compound decomposes within temporary hard water? [H]

A26 Temporary hard water contains Hydrogen carbonate ions (HCO3-) that decompose on heating

to produce Carbonate ions which react with Calcium and Magnesium ions to form precipitates.

Q27 Why does using hard water increase costs?

A27 - More soap is needed to get a lather OR limescale formed on elements of appliances.

Q28 What causes the efficiency of heating systems and kettles to be reduced when hard water is heated in kettles?

A28 - Limescale build up (Calcium carbonate) reduces efficiency of the heating element.

Q29 Write down the word equation that demonstrates the formation of Calcium hydrogen carbonate.

A29 - Calcium hydrogencarbonate Calcium carbonate + Water + Carbon dioxide

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Q30 Hard water can be made soft by removing the dissolved Calcium and Magnesium ions. Describe the TWO methods in which this can be done.

A30 - Adding Sodium carbonate, which reacts with the Calcium and Magnesium ions to form a precipitate of Calcium carbonate and Magnesium carbonate.

- Using commercial water softeners such as ion exchange columns containing Hydrogen ions or Sodium ions, which replace the Calcium and Magnesium ions when hard water passes through the column.

C3.2.2 Purifying water (p80)

Q31 Fill in the blanks: Water of the correct quality is essential for life. For humans, drinking water should have sufficiently _____ levels of _________ ___________ and _______.

A31 - low, dissolved salts, microbes.

Q32 In this question you will be assessed on using good English, organising information clearly and using specialist terms where appropriate. Explain the stages needed in order to make water clean to drink. (6 marks)

A32 - Screening o As the water enters the water treatment works, it passes through a screen. o This is made from bars of metal placed together. o These catch large objects such as leaves and twigs.

- Settlement Tank o Sand and soil settle out.

- Adding Aluminium sulphate and Lime to water o Makes particles of dirt clump together and settle.

- Filter (bed) o Fine sand filters remaining particles (insoluble solid).

- Chlorination o Water may contain some harmful bacteria. o Therefore adding chlorine kills the bacteria.

- Arrival of water to buildings o The pH of the water is checked and corrected so that it is neutral. o It is then stored in large tanks and service reservoirs ready to be pumped to

homes, schools, offices, factories etc.

Q33 Discuss the advantages and disadvantages of adding chlorine and fluoride to drinking water.

A33 - Fluorine helps to reduce tooth decay. - Chlorine is added to prevent disease. - Some studies have linked adding Chlorine to water with an increase in certain cancers. - Chlorine can react with other natural substances in water to produce toxic by-products

which some people think could cause cancer. - In high doses, Fluoride can cause cancer and bone problems in humans. - There is a concern about whether it is right to ‘mass medicate’ – people can choose

whether to use a Fluoride toothpaste, but they cannot choose whether their tap water has added Fluoride.

- Levels of chemicals added to drinking water need to be carefully monitored.

Q34 How does an ion exchange work?

A34 - Calcium / Magnesium ions are replaced for Hydrogen / Sodium ions.

Q35 How can totally pure water be produced and what can it be used for?

A35 - Totally pure water with nothing dissolved in it can be produced by distillation. - Distillation involves boiling water to make steam and condensing the steam. - Distilled water is used in chemistry labs.

Q36 What are the disadvantages of producing drinking water by distillation?

A36 - It is expensive because large amounts of energy are needed to heat the seawater. - It increases the use of fossil fuels - which are non-renewable resources. - Carbon dioxide emissions from burning fossil fuels contribute to global warming.

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Q37 In this question you will be assessed on using good English, organising information clearly and using specialist terms where appropriate. Explain how you would carry out titration to compare the hardness of water samples.

(6 marks)

A37 1. Fill a burette with 50cm3 of soap solution. 2. Add 50cm3 of the first water sample into a flask. 3. Use a burette to add 1cm3 of soap solution to the flask. 4. Put a bung in the flask and shake for 10 seconds. 5. Repeat steps 3 and 4 until a lasting lather (bubble cover the surface for at least

30 seconds) is formed. 6. Record how much soap was needed to create a lasting lather. 7. Repeat steps 1 to 6 with the other water samples. 8. Boil, fresh samples of each type of water for 10 minutes, and repeat the experiment.

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C3.3.1 Energy from reactions (p89-p92)

Q38 Explain how fuel energy is calculated using a calorimeter.

A38 1. Put 50g of water in the copper can and record its (starting) temperature. 2. Heat the water using the flame from the burning fuel. 3. Record the final temperature of the water. 4. Weight the spirit burner and lid again.

Q39 Describe how you would carry out the energy changes for neutralisation reactions or for reactions of solids with water.

A39 To do this experiment: 1. Add a known volume of the first reactant (in solution) to the insulated container. 2. Record the starting temperature of the liquid. 3. Add the second reactant (either in solution or as a solid powder). 4. Replace the lid and stir the reaction mixture. 5. Record the maximum temperature that the reaction mixture reaches.

Q40 What formula can used to calculate the amount of energy transferred during a chemical reaction? You must state the meaning of the letter and the unit(s) used.

A40 Q = mc ΔT - Q = the heat energy transferred (joule, J). - m = the mass of the liquid being heated (grams, g). - c = the specific heat capacity of the liquid (joule per gram degree Celsius, J/g°C). - ΔT = the change in temperature of the liquid (degree Celsius, °C).

Q41 50 cm3 of an acid was added to 50 cm3 of an alkali. The mixture was stirred and the temperature increased from 18°C to 28°C. What was the amount of energy released in J? (3 marks)

A41 - Step 1: Calculate the temperature change, ΔT o 28 – 18 = 10°C

- Step 2: Use Q = mc ∆T o Remember that c = 4.2 J/g°C for liquids (unless you are told otherwise): o Q = mc ∆T o Q = (50 + 50) × 4.2 × 10 = 4200 J

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Q42 In an experiment, Ethanol was burnt from a spirit burner and the energy released was used to heat 50 g of water. The starting temperature of the water was 19°C but by the end of the reaction, the temperature had risen to 41°C. The mass of fuel in the spirit burner was initially 40.0 g, but this had decreased to 38.5 g by the end of the reaction. Calculate the energy change in kJ/g of fuel. (5 marks)

A42 - Step 1: Calculate the temperature change, ΔT o 41 – 19 = 22 °C

- Step 2: Use Q = mc ∆T o Remember that c = 4.2 J/g°C for liquids (unless you are told otherwise): o Q = mc ΔT o Q = 50 × 4.2 × 22 = 4620 J o Q = 4.62 kJ

- Step 3: Calculate the mass of fuel burnt o 40.0 – 38.5 = 1.5 g

- Step 4: Divide energy released by mass of fuel burnt o Energy change = 4.62 ÷ 1.5 = 3.08 kJ/g

Q43 What happens to the bonds of both products and reactants during a chemical reaction?

A43 During a chemical reaction: - bonds in the reactants are broken. - new bonds are made in the products.

Q44 What is an exothermic reaction? Do products have more or less energy than reactants in exothermic reactions?

A44 - Exothermic reactions give out heat energy to the surroundings. - This means that energy is being lost so the products have less energy than the

reactants.

Q45 What is an endothermic reaction? Do products have more or less energy than reactants in endothermic reactions?

A45 - Endothermic reactions absorb heat energy from the surroundings, making the temperature of the surroundings cooler.

- This means that energy is gained, so the products have more energy than the reactants.

Q46 Label the energy level diagram of figure 1, an exothermic reaction and figure 2, an endothermic reaction.

Figure 1 Figure 2

A46 Figure 1 1- reactants, 2- products, 3- energy, 4- progress of reaction, 5- released. Figure 2 1-reactants, 2- products, 3- energy, 4- progress of reaction, 5-absorbed.

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Q47

Figure 3 Label figure 3, showing the energy changes in chemical reactions.

A47 1-activation energy, 2- overall change in energy (△H), 3- products, 4- reactants.

Q48 Study figure 3. Explain what is meant by number 1 on the diagram.

A48 - Activation energy represents the minimum energy needed by reacting particles to break their bonds.

Q49 Draw figure 3 and show on the diagram how a catalyst may have an effect.

A49

Q50 Describe the advantages of lowering the activation energy.

A50 - It means that reactions happen more quickly and are more economical in terms of the energy required for industrial-scale reactions.

Q51 Complete questions 4 and 5 on page 126 in the CGP GCSE Chemistry Workbook.

A51 4) (a) (412 × 4) + (2 × 498) = 1648 + 996 = 2644 kJ/mol (b) (2 × 743) + (4 × 463) = 1486 + 1852 = 3338 kJ/mol (c) △H = 2644 – 3338 = -694 kJ/mol 5) (391 × 4) + 158 + 498 = 1564 + 656 = 2220 945 + (4 × 463) = 945 + 1852 = 2797

△H = 2220 – 2797 = -577 kJ/mol

Q52 Describe the TWO ways in which Hydrogen is used to power cars.

A52 - Burning hydrogen directly in the engine o Hydrogen gas can be burnt in Oxygen as a fuel in the combustion engines of

vehicles. o Hydrogen + Oxygen → Water

- Hydrogen fuel cells o In a Hydrogen fuel cell, Hydrogen reacts with Oxygen without burning. o The energy released is used to generate electricity, which is used to drive an

electric motor.

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Q53 Discuss the advantages and disadvantages of hydrogen as a fuel.

A53 Advantages Disadvantages

- unlike petrol and diesel, Hydrogen does not generate carbon dioxide when burnt.

- Hydrogen fuel cells are very efficient.

- few filling stations sell Hydrogen. - Hydrogen must be compressed

and liquefied, and then stored in tough, insulated fuel tanks.

- atmospheric pollution may be generated during the production of Hydrogen.

- Hydrogen fuel cells do not work at very low temperatures, and they may also require a Platinum catalyst (Platinum is expensive and prone to contamination by impurities).

Q54 Evaluate the use of fuel cells.

A54 Advantages Disadvantages

- Reduces pollution caused by burning fossil fuels, the only by product is water.

- Have a higher efficiency than diesel or gas engines.

- Maintenance is more simple - less moving parts in the system.

- Production, transportation, distribution and storage of Hydrogen is difficult.

- Driving range of cars is shorter than in a traditional vehicles.

- Refuelling and starting times of fuel cell vehicles are longer.

- Currently expensive to produce, uses some use expensive materials, e.g. Platinum.

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C3.4.1 Analysing substances (p93 and p94, p87 and p88)

Q55 Complete the table below showing the metal ion and the colour the flame goes.

METAL ION FLAME COLOUR

Lithium

Sodium

Potassium

Calcium

Barium

A55 METAL ION FLAME COLOUR

Lithium Crimson

Sodium Yellow

Potassium Lilac

Calcium Red

Barium Green

Q56 Complete the table below showing the metals ions and the colour the precipitate goes with Sodium hydroxide solution.

METAL ION PRECIPITATE COLOUR

Calcium, Ca2+

Copper(II), Cu2+

Iron(II), Fe2+

Iron(III), Fe3+

Aluminium, Al3+

Magnesium, Mg2+

A56 METAL ION PRECIPITATE COLOUR

Calcium, Ca2+ White

Copper(II), Cu2+ Blue

Iron(II), Fe2+ Green

Iron(III), Fe3+ Brown

Aluminium, Al3+ White at first, but then redissolves in excess NaOH to form a colourless solution

Magnesium, Mg2+ White

Q57 Describe the test for Carbonate ions.

A57 - You can test for the prescence of Carbon dioxide by bubbling it through limewater. The limewater turns cloudy if carbon dioxide is present.

- This can be used to test for Carbonate ions since carbonates react with dilute acids to form Carbon dioxide.

Q58 This question is about halide ions. How would you test for Chloride, Bromide or Iodide ions?

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A58 - Add dilute Nitric acid, followed by Silver nitrate solution.

Q59 Complete the table, which shows the precipitate formed and the colour of precipitate of the halide ions.

HALIDE ION PRECIPITATE FORMED COLOUR OF PRECIPITATE

Chloride, Cl–

Bromide, Br–

Iodide, I–

A59 HALIDE ION PRECIPITATE FORMED COLOUR OF PRECIPITATE

Chloride, Cl– Silver chloride, AgCl White

Bromide, Br– Silver bromide, AgBr Cream

Iodide, I– Silver iodide, AgI Yellow

Q60 Describe the test for Sulphate ions.

A60 - Add dilute Hydrochloric acid, followed by Barium chloride solution. - The presence of a white precipitate of Barium sulphate shows the presence of Sulphate

ions in the solution.

Q61 Describe what a titration is.

A61 - Titrations are used to determine the volumes of acid and alkali needed to react together to produce a neutral solution.

- Titrations are carried out using a piece of apparatus called a burette, along with a suitable indicator.

Q61 In this question you will be assessed on using good English, organising information clearly and using specialist terms where appropriate. Describe how a titration experiment is carried out. (6 marks)

A61 1. Add a known volume of alkali into a conical flask using a pipette. 2. Add a few drops of indicator. 3. Pour some acid into a burette, and record the reading. 4. Open the tap, add a small amount of acid and swirl the conical flask to mix. 5. Add acid until the solution is neutral as shown by the colour change in the indicator. 6. Repeat three times.

Q62 What formula is used to calculate the concentration in moles per dm3? State the units. [H]

A62 Concentration (mol/dm3) = number of moles / volume (in dm3)

Q63 What formula is used to calculate the concentration in grams per dm3? State the units. [H]

A63 Number of moles = mass (g) / relative formula mass.

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C3.5.1 Making Ammonia (p81 and p82)

Q64 How is ammonia produced?

A64 - Ammonia is produced using a reaction between Nitrogen and Hydrogen called the Haber process.

Q65 Describe how Nitrogen and Hydrogen are obtained.

A65 - Hydrogen is obtained by reacting natural gas (mostly Methane) with steam, or by cracking oil fractions.

- Nitrogen is obtained from the air. Air is 78 per cent Nitrogen; nearly all the rest is Oxygen. When Hydrogen is burned in air, the Oxygen combines with the Hydrogen - leaving Nitrogen behind.

Q66 Label the letters on Figure 4 of the Haber process.

Figure 4

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A66 a- Nitrogen from air b- Hydrogen from natural gas c- compressor d- Hydrogen and Nitrogen in e- Iron catalyst beds f- Nitrogen, Hydrogen and Ammonia out g- cooling tank/condenser h- Hydrogen and Nitrogen i- liquid Ammonia j- Ammonia out

Q67 In this question you will be assessed on using good English, organising information clearly and using specialist terms where appropriate. Explain what is happening at each stage of the Haber process. Use the numbers on Figure 4 to help you. (6 marks)

A67 Stage 1

Having obtained the Hydrogen and Nitrogen gases (from natural gas and the air respectively), they are pumped into the compressor through pipes.

Stage 2

The gases are pressurised to about 200 atmospheres of pressure inside the compressor.

Stage 3

The pressurised gases are pumped into a tank containing beds of Iron catalyst at about 450°C. In these conditions, some of the Hydrogen and Nitrogen will react to form Ammonia.

Stage 4

The unreacted Nitrogen and Hydrogen, together with the Ammonia, pass into a cooling tank. The cooling tank liquefies the Ammonia, which can be removed into pressurised storage vessels.

Stage 5

The unreacted Hydrogen and Nitrogen gases are recycled by being fed back through pipes to pass through the hot Iron catalyst beds again.

Q68 What is a closed system? [H]

A68 - A closed system is a system in which no reactants are added and no products are removed.

Q69 When a reversible reaction occurs in a closed system, what is reached? [H]

A69 - When a reversible reaction happens in a closed system, equilibrium is reached in which the rate of the forward reaction is the same as the backward reaction.

Q70 What do the relative amounts of all the reacting substances at equilibrium depend on? [H]

A70 - the conditions of the reaction.

Q71 Fill in the blanks: In a reversible reaction the position of equilibrium depends very strongly on the ___________ and ____________ surrounding the reaction. [H]

A71 - temperature, pressure (any order)

Q72 What happens when the temperature increases in a reversible reaction? [H]

A72 - If the temperature is increased, the yield from the endothermic reaction increases (and the yield from the exothermic reaction decreases).

Q73 What happens when the temperature decreases in a reversible reaction? [H]

A73 - If the temperature is decreased, the yield from the endothermic reaction decreases (and the yield from the exothermic reaction increases).

Q74 What happens when the pressure is raised in a reversible reaction? [H]

A74 - It will encourage the reaction which produces less volume.

Q75 What happens when the pressure is lowered in a reversible reaction? [H]

A75 - It will encourage the reaction which produces more volume.

Q76 Explain why adding a catalyst would not affect the equilibrium position. [H]

A76 - Catalysts speed up both the forward and backward reactions by the same amount. - So, adding a catalyst means the reaction reaches equilibrium quicker, but you end with

the same amount of product as you would without the catalyst.

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Q77 Evaluate the conditions used in industrial processes in terms of energy requirements.

A77 - Less energy is needed to break bonds in the Nitrogen and Hydrogen molecules than is released in the formation of the ammonia molecules.

- A low temperature favours the production of Ammonia but the reaction is slow. - A high temperature would make Ammonia form faster (and break down faster). A

compromised temperature used is 450˚C. - A high pressure favours the production of Ammonia but the reaction is expensive. A

compromise pressure used is 200 atmospheres.

Q78 Describe the conditions used in the manufacture of Ammonia to increase the rate of reaction. (4 marks)

A78 rate of reaction is increased Iron/powder acts as catalyst at higher temperatures at higher pressures any 4 answers for 1 mark each.

Q79 Describe and explain the conditions used in the manufacture of Ammonia to increase the yield. (7 marks)

A79 yield of Ammonia is increased at higher pressure since equilibrium is moved to the right (idea) but there is high cost in manufacturing the plant to withstand very high pressures so optimum* pressure of about 250 atmospheres is used (* – just quoting the figures not enough) very high pressure increases safety risk yield of Ammonia is increased at lower temperatures since equilibrium is moved to the right but the rate of reaction is reduced at lower temperatures so process becomes uneconomic optimum temperature of about 450°C is used yield of ammonia is increased if the Ammonia is removed from the reaction mixture since equilibrium is moved to the right (idea) so Ammonia is removed as a liquid after cooling and condensing unreacted Nitrogen and Hydrogen recycled (credit Nitrogen and Ammonia because of misprint on the diagram) NB Answers in (b) must clearly relate to yield not to rate (except for the qualification w.r.t. temperature) any 7 points for 1 mark each

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C3.6.1 Alcohols (p83)

Q80 What are Alcohols?

A80 - Alcohols are actually a family of organic compounds, all of which contain a –OH functional group.

Q81 What is the general formula for an Alcohol?

A81 - CnH2n+1OH

Q82 What properties do the first three Alcohols share?

A82 - They are colourless liquids that dissolve in water to form a neutral solution. - They react with Sodium to produce Hydrogen and a salt. - They burn in the air, releasing energy and producing Carbon dioxide and Water. - They are used as fuels and solvents, and Ethanol is the main alcohol in alcoholic

drinks.

Q83 What is Methylated spirit and describe its use?

A83 - Ethanol with chemicals (e.g. Methanol) added to it. - It is used to clean paint brushes and as a fuel.

Q84 State the formula and draw the structures for the three alcohols.

A84 Methanol Ethanol Propanol

CH3OH CH3CH2OH

CH3CH2CH2OH

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C3.6.2 Carboxylic acids (p84)

Q85 What are Carboxylic acids?

A85 - The Carboxylic acids are a homologous series of organic compounds.

Q86 What functional group do Carboxylic acids share?

A86 - Carboxylic acids all contain the same functional group –COOH.

Q87 What do the names of Carboxylic acids end in?

A87 - The names of Carboxylic acids end in ‘-oic acid’ – eg ethanoic acid.

Q88 Complete the table below:

CARBOXYLIC ACID NUMBER OF C ATOMS

STRUCTUAL FORMULA

DISPLAYED FORMULA

Methanoic acid

Ethanoic acid

Propanoic acid

A88 CARBOXYLIC ACID

NUMBER OF C ATOMS

STRUCTURAL FORMULA

DISPLAYED FORMULA

Methanoic acid 1 HCOOH

Ethanoic acid 2 CH3COOH

Propanoic acid 3 CH3CH2COOH

Q89 Complete the following reaction: Ethanoic acid + Sodium carbonate ______+ _______

A89 - Carbon dioxide + Sodium ethanoate

Q90 What is vinegar?

A90 - Vinegar is an aqueous solution containing Ethanoic acid.

Q91 How is Ethanoic acid formed?

A91 - Ethanoic acid is formed from the mild oxidation of the Ethanol (which is an alcohol).

Q92 How is the formation of Ethanoic acid achieved?

A92 - The addition of chemical oxidising agents - such as acidified Potassium dichromate. - The action of microbes in aerobic conditions (in the presence of Oxygen). This happens

on a small scale when a bottle of wine is left open and exposed to air. On a commercial scale, it is achieved in a fermenter using Acetic acid bacteria.

Q93 Describe the properties of Carboxylic acids. [H]

A93 Carboxylic acids: - dissolve in water to produce acidic solutions. - react with Carbonates to produce Carbon dioxide - react with alcohols in the presence of an acid catalyst to produce esters. - do not ionise completely when dissolved in water and so are weak acids. - aqueous solutions of weak acids have a higher pH value than aqueous solutions of

strong acids with the same concentration.

Q94 How are Carboxylic acids useful in industry?

A94 - Carboxylic acids with longer chains of carbon atoms are used to make soaps and detergents.

- Carboxylic acids are also used in the preparation of esters.

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C3.6.3 Esters (p85)

Q95 What are esters? What functional group do esters share?

A95 - Esters are organic compounds formed by the reaction of an alcohol with a carboxylic acid. They have the functional group –COO–.

Q96 What properties do esters have in common?

A96 - they are volatile - they are liquids that become vapours easily. - they have distinctive ‘fruity’ smells.

Q97 How do the properties of esters make them useful in the industry?

A97 - These properties make esters very useful as food flavourings, and as perfumes in cosmetics.

Q98 How is Ethyl ethanoate made?

A98 - Ethyl ethanoate is the ester made from Ethanol and Ethanoic acid. - Sulphuric acid is added to act as a catalyst in the reaction.

Q99 What products are formed when Ethanol reacts with Ethanoic acid?

A99 - Ethyl ethanoate and water are formed as a result of Ethanol’s reaction with Ethanoic acid.

- This reaction is reversible.

Q100 What products are formed when ethanol reacts with ethanoic acid? This time, write a balanced symbol equation.

A100 CH3CH2OH(aq) + CH3COOH(aq) CH3CH2OOCCH3(aq) + H2O(l)

Q101 Using your answer to Q100, draw the structural formula for each one.

A101

Q102 Complete the table below:

Name of alcohol Name of carboxylic acid Name of ester

Ethanol Propanoic acid

Butanol Methanoic acid

Pentanol Ethanoic acid

A102 Name of alcohol Name of carboxylic acid Name of ester

Ethanol Propanoic acid Ethyl propanoate

Butanol Methanoic acid Butyl methanoate

Pentanol Ethanoic acid Pentyl ethanoate