Ch 8 Practice Problems

Ch 8 Practice Problems 1. What combination of substances will give a buffered solution that has a ph of 5.05? Assume each pair of substances is dissolved in 5.0 L of water. (K a for NH 4 = 5.6 10 10 ; K a for C 5H 5NH = 5.9 10 6 ) A) 1.0 mol NH 3 and 1.5 mol NH 4Cl B) 1.5 mol NH 3 and 1.0 mol NH 4Cl C) 1.0 mol C 5H 5N and 1.5 mol C 5H 5NHCl D) 1.5 mol C 5H 5N and 1.0 mol C 5H 5NHCl 2. You have solutions of 0.200 M HNO 2 and 0.200 M KNO 2 (K a for HNO 2 = 4.00 10 4 ). A buffer of ph 3.000 is needed. What volumes of HNO 2 and KNO 2 are required to make 1 L of buffered solution? A) 500 ml of each B) 286 ml HNO 2; 714 ml KNO 2 C) 413 ml HNO 2; 587 ml KNO 2 D) 714 ml HNO 2; 286 ml KNO 2 E) 587 ml HNO 2; 413 ml KNO 2 3. Calculate [H ] in a solution that is 0.34 M in NaF and 0.58 M in HF. (K a = 7.2 10 4 ) A) 0.58 M B) 4.2 10 4 M C) 1.2 10 3 M D) 2.0 10 2 M E) 1.1 10 4 M 4. Calculate the ph of a solution made by mixing 33.0 ml of 0.340 M NaA (K a for HA = 1.0 10-8 ) with 26.4 ml of 0.100 M HCl. A) 8.63 B) 7.49 C) 8.51 D) 7.62 E) 8.00 5. Consider a solution of 2.0 M HCN and 1.0 M NaCN (K a for HCN = 6.2 10 10 ). Which of the following statements is true? A) The solution is not a buffer because [HCN] is not equal to [CN ]. B) The ph will be below 7.00 because the concentration of the acid is greater than that of the base. C) [OH ] > [H ] D) The buffer will be more resistant to ph changes from addition of strong acid than to ph changes from addition of strong base. E) All of these statements are false. 6. Which of the following will not produce a buffered solution? A) 100 ml of 0.1 M Na 2CO 3 and 50 ml of 0.1 M HCl B) 100 ml of 0.1 M NaHCO 3 and 25 ml of 0.2 M HCl C) 100 ml of 0.1 M Na 2CO 3 and 75 ml of 0.2 M HCl D) 50 ml of 0.2 M Na 2CO 3 and 5 ml of 1.0 M HCl E) 100 ml of 0.1 M Na 2CO 3 and 50 ml of 0.1 M NaOH 7. For ammonium ion, K a is 5.6 10-10. To make a buffered solution with ph 10.0, the ratio of NH 3 to NH 4Cl must be A) 1.8 : 1 B) 1 : 5.6 C) 0.18 : 1 D) 5.6 : 1

8. How much solid NaCN must be added to 1.0 L of a 0.5 M HCN solution to produce a solution with ph 7.0? K a = 6.2 10 10 for HCN. A) 0.0034 g B) 11 g C) 160 g D) 24 g E) 0.15 g 9. For 105.0 ml of a buffer that is 0.40 M in HOCl and 0.36 M in NaOCl, what is the ph after 13.4 ml of 1.5 M NaOH is added? K a for HOCl = 3.5 10 8. (Assume the volumes are additive.) A) 7.03 B) 6.91 C) 7.41 D) 7.50 E) 7.88 10. What is the ph of a solution that results when 0.010 mol HNO 3 is added to 655.0 ml of a solution that is 0.22 M in aqueous ammonia and 0.50 M in ammonium nitrate. Assume no volume change. (K a for NH 4 = 5.6 10-10.) A) 5.15 B) 9.66 C) 4.34 D) 8.85 E) 8.90 11. Which of the following solutions will be the best buffer at a ph of 4.74? (K a for HC 2H 3O 2 is 1.8 10-5 ; K a for NH 4 is 5.6 10-10.) A) 0.10 M HC 2H 3O 2 and 0.10 M NaC 2H 3O 2 B) 5.0 M HC 2H 3O 2 and 5.0 M NH 4Cl C) 0.10 M NH 3 and 0.10 M NH 4Cl D) 5.0 M HC 2H 3O 2 and 5.0 M NaC 2H 3O 2 E) 5.0 M HC 2H 3O 2 and 5.0 M NH 3 12. A solution of hydrochloric acid of unknown concentration was titrated with 0.16 M NaOH. If a 350-mL sample of the HCl solution required exactly 17 ml of the NaOH solution to reach the equivalence point, what was the ph of the HCl solution? A) 11.89 B) 2.11 C) 2.13 D) 0.16 E) 0.52 13. What is the molarity of a sodium hydroxide solution if 25.0 ml of this solution reacts exactly with 22.30 ml of 0.253 M sulfuric acid? A) 0.113 M B) 0.226 M C) 0.284 M D) 0.451 M E) 0.567 M 14. Equal volumes of 0.1 M HCl and 0.1 M HC 2H 3O 2 are titrated with 0.1 M NaOH. Which of the following would be equal for both titrations? A) the initial ph B) the ph at the halfway point C) the ph at the equivalence point D) the volume of NaOH added to reach the equivalence point E) two of the above

15. A 74.60-mL sample of 0.0758 M HCN (K a = 6.2 10 10 ) is titrated with 0.610 M NaOH. What volume of 0.610 M NaOH is required to reach the stoichiometric point? A) 600 ml B) 9.27 ml C) 74.6 ml D) 5.65 ml E) 0.00167 ml 16. Which of the following is the net ionic equation for the reaction that occurs during the titration of nitrous acid with potassium hydroxide? A) HNO 2 K OH KNO 2 H 2O B) HNO 2 H 2O NO 2 H 3O C) HNO 2 KOH K NO 2 H 2O D) HNO 2 OH NO 2 H 2O E) H OH H 2O 17. The ph at the equivalence point of a titration of a weak acid with a strong base is A) less than 7.00. B) equal to 7.00. C) greater than 7.00. D) More data are needed to answer this question. 18. If 16 ml of 0.74 M HCl is added to 114 ml of 0.26 M NaOH, what is the final ph? A) 13.14 B) 0.86 C) 13.36 D) 0.64 E) 7.00 19. A 50.00-mL sample of 0.100 M KOH is titrated with 0.100 M HNO 3. Calculate the ph of the solution after the 52.00 ml of HNO 3 is added. A) 6.50 B) 3.01 C) 2.71 D) 2.41 20. A 74.0-mL sample of 0.13 M HNO 2 (K a = 4.0 10 4 ) is titrated with 0.14 M NaOH. What is the ph after 25.8 ml of NaOH has been added? A) 7.00 B) 10.38 C) 3.62 D) 3.18 E) 2.97 21. A 75.0-mL sample of 0.0500 M HCN (K a = 6.2 10 10 ) is titrated with 0.500 M NaOH. What is [H ] in the solution after 3.0 ml of 0.500 M NaOH has been added? A) 1.0 10 7 M B) 4.1 10 10 M C) 5.2 10 13 M D) 9.3 10 10 M 22. A 100.-mL sample of 0.10 M HCl is mixed with 50. ml of 0.10 M NH 3. What is the resulting ph? (K a for NH 4 = 5.6 10 10 ) A) 12.52 B) 3.87 C) 1.30 D) 7.85 E) 1.48

23. After adding 25.0 ml of 0.100 M NaOH to 100.0 ml of 0.100 M weak acid (HA), the ph is found to be 5.90. Determine the value of K a for the acid HA. A) 1.6 10-11 B) 4.2 10-7 C) 2.1 10-5 D) 3.5 10-9 24. The following plot show the ph curves for the titrations of various acids, HA, by 0.10 M NaOH. At the start of the titration, all of the acids were 50.0 ml of 0.10 M HA. Which ph curve corresponds to an acid with Ka = 2 10 6? A) a B) b C) c D) d E) e 25. A 50.0-mL sample of 0.10 M HNO2 is titrated with 0.10 M NaOH. What is the ph after 50.0 ml of NaOH have been added? (K a of HNO 2 is 4.00 x 10-4 ) A) 7.00 B) 1.00 C) 5.95 D) 10.25 E) 8.05 26. Silver chromate, Ag 2CrO 4, has a K sp of 9.0 10 12. Calculate the solubility, in moles per liter, of silver chromate. A) 1.3 10 4 M B) 7.8 10 5 M C) 9.5 10 7 M D) 1.9 10 12 M E) 9.8 10 5 M 27. The concentration of OH in a saturated solution of Mg(OH) 2 is 3.6 10 4 M. What is K sp for Mg(OH) 2? A) 1.3 10 7 B) 4.7 10 11 C) 1.2 10 11 D) 3.6 10 4 28. The solubility of Cd(OH) 2 in water is 1.7 10 5 mol/l at 25 C. What is K sp for Cd(OH) 2? A) 2.0 10 14 B) 4.9 10 15 C) 5.8 10 10 D) 2.9 10 10

29. The solubility of La(IO 3) 3 in a 0.10 M KIO 3 solution is 1.0 10 7 mol/l. Calculate K sp for La(IO 3) 3. A) 1.0 10 8 B) 2.7 10 9 C) 1.0 10 10 D) 2.7 10 27 30. Calculate the concentration of chromate ion, CrO 2 4, in a saturated solution of CaCrO 4 (K sp = 7.1 10 4 ). A) 0.027 M B) 5.0 10 7 M C) 7.1 10 4 M D) 3.5 10 4 M E) 3.5 10 2 M 31. The value of K sp for AgI is 1.5 10 16. Calculate the solubility, in moles per liter, of AgI in a 0.50 M NaI solution. A) 1.7 10 8 mol/l B) 1.2 10 8 mol/l C) 7.5 10 17 mol/l D) 2.8 10-9 mol/l E) 3.0 10 16 mol/l 32. Calculate the solubility of Ca 3(PO 4) 2(s) (K sp = 1.3 10 32 ) in a 1.0 10 2 M Ca(NO 3) 2 solution. A) 5.7 10 14 mol/l B) 6.2 10 7 mol/l C) 1.6 10 14 mol/l D) 3.16 10 12 mol/l Answers: 1. C 2. D 3. C 4. C 5. C 6. E 7. D 8. E 9. E 10. D 11. D 12. B 13. D 14. D 15. B 16. D 17. C 18. A 19. C 20. D 21. D 22. E 23. B 24. D 25. E 26. A 27. E 28. A 29. C 30. A 31. E 32. A