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Topic 9 : Acids and Bases (HL) Practice
1. Which salts will produce an acidic solution when dissolved in water? I. CH 3 COOK II. NH 4 NO 3 III. Al 2 (SO 4 ) 3 A. I and II only B. I and III only C. II and III only D. I, II and III (Total 1 mark) 2. The K b value for a base is 5.0 × 10 –^2 mol dm–^3 at 298 K. What is the K a value for its conjugate acid at this temperature? A. 5.0 × 10 –^2 B. 2.0 × 10 –^6 C. 2.0 × 10 –^12 D. 2.0 × 10 –^13 (Total 1 mark) 3. Which compounds can be mixed together as solutions of equal volume and concentration to form a buffer solution? A. Nitric acid and potassium hydroxide B. Nitric acid and potassium nitrate C. Propanoic acid and potassium hydroxide D. Propanoic acid and potassium propanoate (Total 1 mark)
8. Determine the pH of the solution resulting when 100 cm^3 of 0.50 mol dm–^3 HCl(aq) is mixed with 200 cm^3 of 0.10 mol dm–^3 NaOH(aq). ................................................................................................................................................ ................................................................................................................................................ ................................................................................................................................................ ................................................................................................................................................ ................................................................................................................................................ ................................................................................................................................................ ................................................................................................................................................ ................................................................................................................................................ ................................................................................................................................................ ................................................................................................................................................ (Total 5 marks) 9. Based on information in the table below, which acid is the strongest? Acid p K a K a A. HA 2.0 – B. HB – (^1) × 10 –^3 C. HC 4.0 – D. HD – (^1) × 10 –^5 (Total 1 mark)
11. The graph below shows the titration curve of 25 cm^3 of 0.100 mol dm–^3 of hydrochloric acid with sodium hydroxide, of 0.100 mol dm–^3 concentration. The indicator methyl orange was used to determine the equivalence point. Methyl orange has a pH range of 3.2–4.4. If the hydrochloric acid was replaced by ethanoic acid of the same volume and concentration, which property of the titration would remain the same? A. The initial pH B. The pH at the equivalence point C. The volume of strong base, NaOH, needed to reach the equivalence point D. The colour of the titration mixture just before the equivalence point is reached (Total 1 mark)
14. Salts may form neutral, acidic or alkaline solutions when dissolved in water. (i) Explain why a solution of sodium chloride is neutral but sodium carbonate forms an alkaline solution when it dissolves in water. ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... (2) (ii) Explain why iron(III) chloride, [Fe(H 2 O) 6 ]Cl 3 , forms an acidic solution in water. ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... (2) (Total 4 marks) 15. What is the K b expression for the reaction of ethylamine with water? A. K b = [CH 3 CH 2 NH 3 +][OH–] B. K b = C. K b = D. K b = [CH 3 CH 2 NH 2 ][H 2 O] (Total 1 mark)
19. p K w for water at 10 °C = 14.54. What is the pH of pure water at this temperature? A. 6. B. 7. C. 7. D. 7. (Total 1 mark) 20. What is K b for the aqueous fluoride ion given that K w is 1.0 × 10 - 14 and K a for HF is 6.8 × 10 - 4 at 298 K? A. B. (6.8 × 10 –^4 )(1.0 × 10 –^14 ) C. D. 6.8 × 10 –^4 (Total 1 mark) 21. Which of the following could be added to a solution of ethanoic acid to prepare a buffer? A. Sodium hydroxide B. Hydrochloric acid C. Sodium chloride D. More ethanoic acid (Total 1 mark)
22. Which aqueous solution has a pH less than 7? A. KNO 3 (aq) B. Na 2 CO 3 (aq) C. [Fe(H 2 O) 6 ]Cl 3 (aq) D. CH 3 COONa(aq) (Total 1 mark) 23. Water is an important substance that is abundant on the Earth’s surface. (i) State the expression for the ionic product constant of water, K w. (1) (ii) Explain why even a very acidic aqueous solution still has some OH–^ ions present in it. (1) (iii) State and explain the effect of increasing temperature on the value of K w given that the ionization of water is an endothermic process. (3) (iv) State and explain the effect of increasing temperature on the pH of water. (2) (Total 7 marks) 24. Buffer solutions resist small changes in pH. A phosphate buffer can be made by dissolving NaH 2 PO 4 and Na 2 HPO 4 in water, in which NaH 2 PO 4 produces the acidic ion and Na 2 HPO 4 produces the conjugate base ion. (i) Deduce the acid and conjugate base ions that make up the phosphate buffer and state the ionic equation that represents the phosphate buffer. (3)
26. Which mixtures act as buffer solutions? I. 100 cm^3 0.1 mol dm–^3 ethanoic acid and 100 cm^3 0.1 mol dm–^3 sodium ethanoate II. 100 cm^3 0.1 mol dm–^3 ethanoic acid and 50 cm^3 0.1 mol dm–^3 sodium hydroxide III. 100 cm^3 0.1 mol dm–^3 ethanoic acid and 100 cm^3 0.5 mol dm–^3 sodium hydroxide A. I and II only B. I and III only C. II and III only D. I, II and III (Total 1 mark) 27. Which solutions have a pH less than 7? I. Na 2 CO 3 (aq) II. [Fe(H 2 O) 6 ]Cl 3 (aq) III. (NH 4 ) 2 SO 4 (aq) A. I and II only B. I and III only C. II and III only D. I, II and III (Total 1 mark)
28. Equal volumes and concentrations of hydrochloric acid and ethanoic acid are titrated with sodium hydroxide solutions of the same concentration. Which statement is correct? A. The initial pH values of both acids are equal. B. At the equivalence points, the solutions of both titrations have pH values of 7. C. The same volume of sodium hydroxide is needed to reach the equivalence point. D. The pH values of both acids increase equally until the equivalence points are reached. (Total 1 mark) 29. Bromophenol blue changes from yellow to blue over the pH range of 3.0 to 4.6. Which statement is correct? A. Molecules of bromophenol blue, HIn, are blue. B. At pH < 3.0, a solution of bromophenol blue contains more ions, In–, than molecules, HIn. C. The p K a of bromophenol blue is between 3.0 and 4.6. D. Bromophenol blue is a suitable indicator to titrate ethanoic acid with potassium hydroxide solution. (Total 1 mark) 30. (a) Ammonia can be converted into nitric acid, HNO 3 (aq), and hydrocyanic acid, HCN(aq). The p K a of hydrocyanic acid is 9.21. (i) Distinguish between the terms strong and weak acid and state the equations used to show the dissociation of each acid in aqueous solution. (3) (ii) Deduce the expression for the ionization constant, K a, of hydrocyanic acid and calculate its value from the p K a value given. (2) (iii) Use your answer from part (a) (ii) to calculate the [H+] and the pH of an aqueous solution of hydrocyanic acid of concentration 0.108 mol dm–^3. State one assumption made in arriving at your answer. (4)
Sketch the graph that would be obtained for the titration of 25.0 cm^3 of 0.100 mol dm–^3 propanoic acid with 0.100 mol dm–^3 potassium hydroxide using bromophenol blue as an indicator. (The pH range of bromophenol blue can be found in Table 16 of the Data Booklet). (3) (Total 6 marks)
34. 100 cm^3 of a NaOH solution of pH 12 is mixed with 900 cm^3 of water. What is the pH of the resulting solution? A. 1 B. 3 C. 11 D. 13 (Total 1 mark)
35. Ammonia acts as a weak base when it reacts with water. What is the K b expression for this reaction? A. B. C. D. (Total 1 mark) 36. The indicator, HIn is used in a titration between an acid and base. Which statement about the dissociation of the indicator, HIn is correct? HIn (aq) H+^ (aq) + In–^ (aq) colour A colour B A. In a strongly alkaline solution, colour B would be observed. B. In a strongly acidic solution, colour B would be observed. C. [In–] is greater than [HIn] at the equivalence point. D. In a weakly acidic solution colour B would be observed. (Total 1 mark)
(iii) Determine the hydrogen ion concentration and the pH of a 0.010 mol dm–^3 benzoic acid solution. State one assumption made in your calculation. ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... (4) (Total 7 marks)
39. If 20 cm^3 samples of 0.1 mol dm–^3 solutions of the acids below are taken, which acid would require a different volume of 0.1 mol dm–^3 sodium hydroxide for complete neutralization? A. Nitric acid B. Sulfuric acid C. Ethanoic acid D. Hydrochloric acid (Total 1 mark)
40. Which mixture of acid and alkali would produce a buffer solution? Acid Alkali A. (^) 40 cm^3 0.1 mol dm–^3 HCl 60 cm^3 0.1 mol dm–^3 NaOH B. (^) 60 cm^3 0.1 mol dm–^3 HCl 40 cm^3 0.1 mol dm–^3 NaOH C. (^) 40 cm^3 0.1 mol dm–^3 HCl 60 cm^3 0.1 mol dm–^3 NH 3 D. (^) 60 cm^3 0.1 mol dm–^3 HCl 40 cm^3 0.1 mol dm–^3 NH 3 (Total 1 mark) 41. Which aqueous solution would have a pH > 7? A. Sodium sulfate B. Ammonium nitrate C. Sodium ethanoate D. Aluminium nitrate (Total 1 mark) 42. Which indicator would be the most appropriate for titrating aqueous ethylamine, CH 3 CH 2 NH 2 , with nitric acid, HNO 3? A. Bromophenol blue (p K a = 4.1) B. Bromothymol blue (p K a = 7.3) C. Phenol red (p K a = 8.0) D. Thymolphthalein (p K a = 10.0) (Total 1 mark)
