+ H 2 O HPO 4. (a) In this system, there are two acid-base conjugate pairs. These are (1) HPO4

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1 1 The dihydrogenphosphate-hydrogenphosphate ion system is an important buffer in the human body. H 2 PO 4 H 2 O HPO 4 2 H 3 O (a) In this system, there are two acid-base conjugate pairs. These are acid with its conjugate base H 2 H 2 PO 4 / HPO 4 2 O / H 3 O base with its conjugate acid H 2 O / H 3 O HPO 4 2 / H 2 PO 4 H 3 H2 O / H 2 O PO 4 / HPO 4 2 2PO 4 / HPO 4 2 H 3 O / H 2 O (b) formula that can be used for the calculation of the ph of this buffer solution is alculate the ph of this buffer using 2 HPO4 ph = pk a log HPO p K a = 7.20 [HPO 4 ] = mol dm 3 [H 2 PO 4 ] = mol dm (Total for Question = 2 marks) 2 alculate the ph of a solution of Hl, of concentration 0.25 mol dm PhysicsndMathsTutor.com

2 3 Select the correct ph for each of the following solutions. (a) 2 mol dm 3 nitric acid (b) 0.10 mol dm 3 barium hydroxide, a(oh) 2. K w = mol 2 dm (c) mixture of 20 cm 3 of 1.0 mol dm 3 hydrochloric acid and 10 cm 3 of 1.0 mol dm 3 sodium hydroxide (Total for Question = 3 marks) 4 mmonia reacts with water in a reversible reaction. Which are the rønsted-lowry bases? H 2 O and OH NH 3 and OH NH 4 and H 2 O NH 4 and NH 3 PhysicsndMathsTutor.com

3 5 Suggest the most likely ph for each of the following solutions. (a) 5.0 mol dm 3 hydrochloric acid (b) 0. mol dm 3 strontium hydroxide, Sr(OH) 2 K w = mol 2 dm (c) mixture of 20 cm 3 of 1.0 mol dm 3 nitric acid and 10 cm 3 of 1.0 mol dm 3 sodium hydroxide (Total for Question = 3 marks) 6 In liquid ammonia the following equilibrium is present. Identify the rønsted-lowry base(s). NH 2 NH 4 2NH 3 NH 2 only NH 4 only NH 2 and NH 3 NH 4 and NH 3 PhysicsndMathsTutor.com

4 7 solution of potassium manganate(vii) was used to determine the concentration of iron(ii) ions in solution by titration in the presence of excess dilute sulfuric acid. (a) With the potassium manganate(vii) in the burette, the end-point of the reaction is when the solution in the conical flask turns colourless. pink. green. orange. (b) If insufficient acid is added, the titre value is low and a brown precipitate forms. low and a green precipitate forms. high and a brown precipitate forms. high and a green precipitate forms. (Total for Question = 2 marks) 8 Separate 0.1 mol dm 3 aqueous solutions of ammonia, methylamine and phenylamine were prepared. Which of the following sequences shows the solutions in order of increasing ph? phenylamine, methylamine, ammonia phenylamine, ammonia, methylamine methylamine, ammonia, phenylamine methylamine, phenylamine, ammonia PhysicsndMathsTutor.com

5 9 The dissociation constant of water, K w, increases with increasing temperature. When the temperature increases, water remains neutral. dissociates less. becomes acidic. becomes alkaline. 10 The reaction between concentrated sulfuric acid and pure ethanoic acid is H 3 OOH H 2 SO 4 H 3 OOH 2 HSO 4 The rønsted-lowry acids in this equilibrium are H 3 OOH and H 2 SO 4 H 3 OOH 2 and HSO 4 H 2 SO 4 and H 3 OOH 2 H 3 OOH and HSO 4 11 n aqueous solution of ethanoic acid is gradually diluted. Which of the following statements is incorrect? The ph decreases. The value of K a is unchanged. The concentration of ethanoic acid molecules decreases. The proportion of ethanoic acid molecules which dissociates increases. PhysicsndMathsTutor.com

6 12 Methyl orange and phenolphthalein are both acid-base indicators. In the titration of a strong acid against a weak alkali methyl orange is a suitable indicator but phenolphthalein is not. phenolphthalein is a suitable indicator but methyl orange is not. both phenolphthalein and methyl orange are suitable indicators. neither phenolphthalein nor methyl orange is a suitable indicator. 13 Which of the following statements is true about all substances that form acidic solutions in water? They are corrosive. They are liquids. They contain hydrogen atoms. They form H (aq) ions. PhysicsndMathsTutor.com

7 14 Select the correct ph for each of the following solutions. (a) Nitric acid, HNO 3, of concentration 2 mol dm 3, assuming it is fully dissociated (b) Sodium hydroxide, NaO H, of concentration 2 mol dm 3, using K w = mol 2 dm (c) Ethanoic acid, H 3 OOH, of concentration 2 mol dm 3, making the usual assumptions. K a = H [ ][ H OO ] 3 [ H OOH] 3 = mol dm 3 (d) The mixture formed when 25 cm 3 of 2 mol dm 3 sodium hydroxide solution is added to 50 cm 3 of 2 mol dm 3 ethanoic acid, for which K a = mol dm (Total for Question = 4 marks) PhysicsndMathsTutor.com

8 H 2 O O 2 H 2 O 3 15 In which of these reactions is the hydrogensulfate ion, HSO 4, behaving as a rønsted- Lowry base? HSO 4 H 3 O 2 SO 4 H 2 O HSO 4 a 2 4 H HSO 4 H 2 O 4 H 3 O HSO 4 O 3 SO 4 HO 3 (Total for Question 1 mark) 16 solution of hydrochloric acid has ph 3.0. When it is made 10 times more dilute, the ph is (Total for Question 1 mark) 17 In which reaction is water acting as a rønsted-lowry acid? H 2 O Hl H 3 O l H 2 O SO 3 H 2 SO 4 H 2 O NH 3 NH 4 OH PhysicsndMathsTutor.com

9 18 Which of the following solutions has the lowest ph? mol dm 3 hydrochloric acid mol dm 3 hydrochloric acid mol dm 3 ethanoic acid mol dm 3 ethanoic acid. 19 n aqueous solution of ammonium chloride, NH 4 l, has a ph of less than 7 because the ammonium ions donate protons to water molecules giving rise to oxonium ions, H 3 O (aq). the chloride ions combine with hydrogen ions from water to form hydrochloric acid, Hl(aq). an aqueous solution of ammonium chloride is unstable and evolves ammonia gas, NH 3 (g), leaving dilute hydrochloric acid. the ammonium chloride reacts with carbon dioxide from the atmosphere giving ammonium carbonate, (NH 4 ) 2 O 3 (aq), and hydrochloric acid, Hl(aq). 20 Which one of the following indicators is most suitable for titrating ethanoic acid with 0.1 mol dm 3 sodium hydroxide? (Refer to page 19 of your data booklet.) Thymol blue (acid) romothymol blue Thymol blue (base) lizarin yellow R PhysicsndMathsTutor.com

10 21 What is the conjugate base of the acid, HO 3? H 2 O 3 O 3 2 OH O 2 22 The ph of a 1.5 mol dm 3 solution of hydrochloric acid, Hl(aq), is (Total for Question 1 mark) 23 Which sequence shows the bases in order of decreasing strength? 6 H 5 NH 2 > H 3 NH 2 > NH 3 NH 3 > H 3 NH 2 > 6 H 5 NH 2 H 3 NH 2 > NH 3 > 6 H 5 NH 2 NH 3 > 6 H 5 NH 2 > H 3 NH 2 (Total for Question 1 mark) PhysicsndMathsTutor.com

11 24 Which of the following is not a reaction of a rønsted-lowry acid and base? H 3 l OH H 3 OH l NH 3 Hl NH 4 l H 2 O HSO 4 H 2 SO 4 OH HO 3 H 2 O 2 O 3 H 3 O (Total for Question 1 mark) 25 Information about four samples of acid is shown below. Sample 1: 1.0 mol dm 3 Hl Sample 2: 1.0 mol dm 3 H 2 SO 4 Sample 3: 0.1 mol dm 3 Hl Sample 4: 0.1 mol dm 3 H 3 OOH Which of the following lists shows the samples in order of increasing ph? 1, 2, 3, 4 4, 3, 2, 1 2, 1, 3, 4 4, 3, 1, 2 (Total for Question 1 mark) In which of the following reactions is nitric acid acting as a base? HNO 3 NaOH NaNO 3 H 2 O HNO 3 H 2 O H 3 O NO 3 HNO 3 H 2 SO 4 H 2 NO 3 HSO 4 HNO 3 NaHO NaNO 3 H 2 O O PhysicsndMathsTutor.com

12 27 The dissociation of ethanoic acid in aqueous solution is represented by H 3 OOH(aq) H 2 O(l) H 3 O (aq) H 3 OO (aq) Which of the following statements is true for this equilibrium? H 3 OOH is an acid and its conjugate base is H 3 OO. H 2 O is an acid and its conjugate base is OH. t equilibrium, the concentrations of each substance are the same. t equilibrium, the reaction from left to right and the reaction from right to left have stopped. 28 Why are aqueous solutions of sodium ethanoate slightly alkaline? The sodium ions react with water to give an alkali. The ethanoate ions react with water to give hydroxide ions. ll sodium salts give alkaline solutions. The sodium ethanoate is fully ionized in solution. 29 solution of a weak acid cannot be titrated with a weak base using an indicator to find the end-point because the ph change is too gradual close to the equivalence point. there are too few H ions to affect the indicator. there are too few OH ions to affect the indicator. the ph change occurs outside the range of any indicator. PhysicsndMathsTutor.com

13 30 t 100, pure water has a ph of 6, whereas at 25 it has a ph of 7. This is because the dissociation of water is endothermic, so the concentration of hydrogen ions is lower at 100 than it is at 25. the dissociation of water is exothermic, so the concentration of hydrogen ions is lower at 100 than it is at 25. the dissociation of water is endothermic, so the concentration of hydrogen ions is higher at 100 than it is at 25. at 100, water has a higher concentration of hydrogen ions than of hydroxide ions. PhysicsndMathsTutor.com