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Worked solutions to student book questions
Chapter 4 Analysing acids and bases
Q1. Antacid tablets should normally be chewed before they are swallowed. Why? A1. Antacid tablets are normally chewed to provide a larger surface area for faster reaction with stomach acids. Q2. A laboratory test to determine how much hydrochloric acid is neutralised by a brand of antacid does not give a complete picture of its effectiveness in the stomach. What other factors might be important? A2. Other factors to consider when deciding an antacid’s effectiveness include the neutralising action of the antacid over a prolonged period (30 minutes, for example), and whether or not the antacid upsets the acid balance in the stomach. The presence and nature of food in the stomach may also affect the neutralisation reaction. Furthermore, some brands claim to have a coating action on the stomach wall which might be unrelated to the neutralising action. Q3. Examine the range of antacids shown in Figure 4.1 on page 37 of the student book. If you were to choose one of these from all the others, what features, apart from its ability to neutralise acid, might influence your choice? A3. The consumer may have a preference for tablets, gels or solutions. He or she could also be influenced by price, attractiveness of packaging and whether or not the medication can be conveniently carried. Q4. Many antacids fizz when dissolved in a glass of water. One such brand lists among its ingredients, sodium hydrogen carbonate and citric acid. Write an ionic equation for the reaction between HCO3–(aq) and H3O+(aq) responsible for the ‘fizz’. A4. HCO3–(aq) + H3O+(aq) → CO2(g) + 2H2O(l) Q5. In each of the following equations: i identify the acids and bases ii name the conjugate acid–base pairs a NH3(aq) + H2O(l) → NH4+(aq) + OH–(aq) b HSO4–(aq) + H2O(l) → H3O+(aq) + SO42–(aq) c NH4+(aq) + S2–(aq) → NH3(aq) + HS–(aq) d CH3COO–(aq) + H3O+(aq) → H2O(l) + CH3COOH(aq)
Heinemann Chemistry 2 4th edition Enhanced
Chapter 4 Analysing acids and bases
Q1. Antacid tablets should normally be chewed before they are swallowed. Why? A1. Antacid tablets are normally chewed to provide a larger surface area for faster reaction with stomach acids. Q2. A laboratory test to determine how much hydrochloric acid is neutralised by a brand of antacid does not give a complete picture of its effectiveness in the stomach. What other factors might be important? A2. Other factors to consider when deciding an antacid’s effectiveness include the neutralising action of the antacid over a prolonged period (30 minutes, for example), and whether or not the antacid upsets the acid balance in the stomach. The presence and nature of food in the stomach may also affect the neutralisation reaction. Furthermore, some brands claim to have a coating action on the stomach wall which might be unrelated to the neutralising action. Q3. Examine the range of antacids shown in Figure 4.1 on page 37 of the student book. If you were to choose one of these from all the others, what features, apart from its ability to neutralise acid, might influence your choice? A3. The consumer may have a preference for tablets, gels or solutions. He or she could also be influenced by price, attractiveness of packaging and whether or not the medication can be conveniently carried. Q4. Many antacids fizz when dissolved in a glass of water. One such brand lists among its ingredients, sodium hydrogen carbonate and citric acid. Write an ionic equation for the reaction between HCO3–(aq) and H3O+(aq) responsible for the ‘fizz’. A4. HCO3–(aq) + H3O+(aq) → CO2(g) + 2H2O(l) Q5. In each of the following equations: i identify the acids and bases ii name the conjugate acid–base pairs a NH3(aq) + H2O(l) → NH4+(aq) + OH–(aq) b HSO4–(aq) + H2O(l) → H3O+(aq) + SO42–(aq) c NH4+(aq) + S2–(aq) → NH3(aq) + HS–(aq) d CH3COO–(aq) + H3O+(aq) → H2O(l) + CH3COOH(aq)
Heinemann Chemistry 2 4th edition Enhanced