chemistry matters ch11 textbk ans

Chemistry Matters for G.C.E. ‘O’ Level Lesson Notes Chapter 11

Chapter 11 Acids and Bases

Answers to Textbook Exercises

Test Yourself 11.1 (page 174)

1. A layer of insoluble barium sulphate is formed from the initial reaction between barium and sulphuric acid. This coats the barium and prevents any further reaction from occurring.

2. X: copper(II) carbonate; Y: hydrochloric acid; Z: zinc

3. The acid only dissociates into free moving ions needed for conducting electricity in the aqueous state (i.e. when dissolved in water).

4. (a) Zn(s) + 2H+(aq) Zn2+(aq) + H2(g)(b) CaCO3(s) + 2H+(aq) Ca2+(aq) + H2O(g) + CO2(g)


1. Zinc oxide and zinc hydroxide

2. Possible answers: Acids turn moist blue litmus paper red while alkalis turn moist red litmus

blue. Acids dissociate in water to give H+ ions while alkalis dissociate to form OH

ions. Acids react with metals, carbonates and bases but alkalis do not react with

metals (except amphoteric metals), carbonates and bases (except oxides of amphoteric metals).

3. Mg(OH)2 + 2HCl MgCl2 + 2H2O


1. Add quicklime (calcium oxide) or slaked lime (calcium hydroxide) to the soil.

2. (a) Lemon juice contains citric acid (weak acid). It dissolves the carbonate but not the iron casing of the kettle.

(b) Ethanoic acid (in vinegar)

3. (a) W or Z with either U, V, X or Y(b) Ammonia: W; Nitric acid: V; Carbonic acid: Y


1. Sulphur dioxide, nitrogen dioxide, carbon dioxide

2. A: amphoteric; B: acidic; C: basic A: e.g. aluminium oxide, Al2O3

B: e.g. phosphorus(V) oxide, P4O10

C: magnesium oxide, MgO


© Marshall Cavendish International (Singapore) Pte. Ltd. of 3


1. A

2. C

Exercise 11 (page 191)

Foundation

1. B 2. C 3. B 4. C 5. C

6. (a) (i) A soluble base (basic oxide) that produces OH ions in aqueous solution, e.g. sodium hydroxide.

(ii) A substance that produces H+ ions in aqueous solution, e.g. hydrochloric acid(iii) An acid reacts with a base to form a salt and water.

e.g. HCl(aq) + NaOH(aq) NaCl(aq) + H2O(l)(b) Boron is non-metal. It forms an acidic solution with water. It reacts with alkalis to

form a salt and water.

7. (a) True. An alkali is a soluble base.(b) False. Hydrochloric acid is an acid but it does not contain oxygen.(c) False. Ammonia (NH3) contains hydrogen but has a pH greater than 7.(d) True. They contain mobile ions that conduct electricity.

8. (a) Sulphuric acid.(b) Sulphur dioxide.(c) Calcium hydroxide.(d) Sulphuric acid.

Challenge

1. D

2. (a) Hydrogen ion (H+) and sulphate ion (SO42–)

(b) (i) To speed up the reaction.(ii) Hydrogen.(iii) Bubbles of gas (effervescence).

(c) (i) All the sulphuric acid has been used up.(ii) Iron(II) sulphate(iii) Filtration.

3. (a) 2Mg(s) + O2(g) 2MgO(s)(b) It turns moist red litmus paper blue and gives off white fumes with hydrogen

chloride.

4. B

5. (a) It is a stronger alkali.(b) Wear gloves to protect skin and goggles to protect eyes.(c) Sodium hydroxide reacts slowly with glass.

6. (a)Method Advantage Disadvantagei) Litmus paper Easy to use Colour change does not show pHii) pH indicator solution

Easy to use The indicator changes to yellow, the colour of the lemon juice, therefore it is hard to detect colour change.



iii) pH meter Fast and accurate

Needs to be kept clean Can be brokenExpensive to buy

(b) A substance in tea (tannin) acts as an indicator and thus changes colour when lemon, which is acidic, is added.

(c) With the use of chromatography

Critical Thinking (page 193)

(a) The cake would not rise properly leaving a flat, hard cake. There would be excess acid present and the food would taste sour.

(b) The cake would taste of excess sodium carbonate (salty).


chemistry matters ch11 textbk ans

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