F.2 IS Workbook Chapter 10 Answers 10.1 Acids and Alkalis Multiple Choice 1-5 A D C B A Fill in the blanks 1. acids 2. bitter 3. mineral, hydrochloric acid, sulphuric acid 4. sodium, potassium, corrosive, plastic gloves 10.2 Acid-Alkali Indicators Multiple Choice 1-5 A B C C D Fill in the blanks 1. (a) blue litmus (b) red litmus 2. (a) pH (b) lower (d) equals to Matching (a) to (iv) (b) to (i) (c) to (v) (e) to (iii) (f) to (iii) (g) to (ii) (c) Neutral (c) higher (d) to (ii) Questions 1. (a) The pH value is between 10 and 12. (b) red (c) water / sodium chloride solution / sugar solution 2. (a) Check the pH value of the liquid soap with a piece of pH paper / a universal indicator. (b) Silk Liquid Soap (c) ABC Liquid Soap (d) Silk Liquid Soap has a pH value of 5.5 which is the same as pH of healthy skin. It is less likely to harm our skin. A soap solution is usually quite alkaline and may irritate / harm our skin. 10.3 Acids and Corrosion 1-5 F T F T T MC 1-5 C A C B D Matching (a) to (iii), (b) to (ii), (c) to (i), (d) to (v), (e) to (iv) Questions 1. (a) The gas must not be hydrogen / must be nitrogen or carbon dioxide. (b) The gas was carbon dioxide. (d) Calcium carbonate 10.4 Safety Related to the Use of Acids and Alkalis MC 1-5 A C D D C Questions 1. (a) Concentrated sulphuric acid (b) Corrosive (c) Wash the affected body part under running water, and take off clothes immediately. 2. (i) Wear safety spectacles. (ii) Wear a laboratory coat (iii) Wear gloves (iv) Dilute the acid in a fume cupboard (v) Add the concentrated sulphuric acid slowly to a large amount of water and stir with a glass rod carefully. 10.5 Acid rain 1-5 F T F T F MC 1-5 B C D D C Questions 1. (a) Rain that has a pH value lower than 5.6. (b) Sulphur dioxide and nitrogen oxides. (c) Calcium carbonate (d) Calcium carbonate in limestone reacts with acid rain. Calcium carbonate dissolves and gives carbon dioxide during the process. 2. (a) Sulphur (b) (i) Corrode building and structures. (ii) Kill fish and plants in lakes and rivers (iii) Slow down plant growth / kill plants and trees (c) (i) Save energy so that less coal and oil products are burnt and a smaller amount of pollutants is released. (ii) Use alternative energy sources that give out a smaller amount of pollutants. (iii) Use high-grade fuels with low sulphur content. 3. A small amount of vinegar was left in the bottle. The water Annie used to water her plants made the soil too acidic and killed the plants. 10.6 Neutralisation Multiple Choice 1-5 DCABD 6-10 BCDAB Questions 1. (a) (b) (c) (d) 2. sulphuric acid / hydrochloric acid / nitric acid W or X W or X (i) Y or Z (ii) neutralization (a) (b) (c) It was used to show the pH value of the solution. The pH value was 13. (i) The pH value of a neutral solution is 7. (ii) 9.0 cm3 (iii) sodium hydroxide + hydrochloric acid sodium chloride + water (iv) evaporation (v) a white residue (vi) It is table salt. (d) (i) The pH value was 2.0. (ii) No, it had a pH value lower than pH 2.0 because when more than 13 cm3 of it was added, the pH value of the solution dropped further. 3. The medicine must be alkaline as it was used to neutralize the acid in his stomach. It should be weakly alkaline because strongly alkaline substances are corrosive and may hurt the stomach. 10.7 MC D D B C Matching (a) to (i) (b) to (iii) (c) to (ii) Questions (a) It is a strong acid that may damage the metal kettle. (b) (i) Vinegar / ethanoic acid (ii) It is not harmful to humans. It contains a weak acid that will not damage the metal kettle if used for a short period of time. Integrated Exercise 1. F 6. F 2. F 7. T 3. T 8. F 4. T 9. T 5. F 10. T 1. B 6. B 11. A 2. A 7. D 12. D 3. B 8. D 4. D 9. A 5. C 10. C Questions 1. (a) (b) (c) (d) (e) A G E F or G (I), (II) and (IV) 2. (a) P and T (b) Both Q and R are blue in ammonia. (c) Q is yellow in both acids. S is colourless in both acids. (d) P is yellow in ethanoic acid and in sodium hydroxide. (e) P is red in a solution with a pH value equal to or less than 2. T is yellow in a solution with a pH value in between 2 and 8. If a solution looks red after adding P and yellow after adding T, it means that the solution has a pH value of about 2. 3. (a) (b) (c) (d) W V Z W 4. (b) Remove the test tube containing the gas from the set-up in (a). Put a burning splint near the mouth of the test tube. If the gas burns with a ‘pop’ sound, it is hydrogen. (c) (i) Hydrogen gas will be given out at a lower rate. (ii) There will be no reaction. / There will be no hydrogen or gas collected. 5. 6. (a) (b) (c) (d) Colourless gas bubbles are given out. (i) The lime water turns milky. (ii) The gas given out is carbon dioxide. Limestone / calcium carbonate Acidic cleaners dissolve / react with them and give out carbon dioxide. (a) (b) concentrated sodium / potassium hydroxide. corrosive property 7. (a) The air in Sai Kung is the least polluted. The pH value of the rainwater collected there was 5.5, which is closest to the pH value of 5.6 of clean rain. (b) (i) The air in Tsuen Wan and Causeway Bay is the most polluted. The pH values of the rainwater collected in these areas were the lowest among the areas shown. This means that the rainwater was highly polluted by acidic pollutants / sulphur dioxide and nitrogen oxides and was the most acidic. (ii) Tsuen Wan: factories and motor vehicles (Tsuen Wan is an industrial area with heavy traffic.) Causeway Bay: motor vehicles (Causeway Bay has heavy traffic.) (c) (i) The rainwater becomes more acidic. (ii) The southern part of Guangdong is heavily polluted with acidic gases / sulphur dioxide and nitrogen oxides released from the factories and power stations there. When these gases are blown from the north-east to HK in winter, the rainwater collected in Sheung Shui and Sai Kung becomes more acidic and the pH value of rainwater decreases. 8. (a) (b) (c) pH paper / universal indicator salt solution and sugar solution (i) lemon juice (ii) caustic soda / sodium hydroxide (d) (i) orange juice / lemon juice (ii) washing soda / sodium carbonate should not be used because it is too alkaline and is corrosive. (e) (i) oven cleaner / drain cleaner (ii) the hazard warning label showing ‘corrosive’. (iii) Wear plastic gloves.