Ch 7 Practice Problems 1. For the equilibrium that exists in an aqueous solution of nitrous acid (HNO 2, a eak acid), the equilibrium constant expression is [H ] [NO 2 ] = [HNO ] 2 [H ][N][O] [HNO 2] = [H ][NO 2 ] 2 [H ] [NO 2 ] = [HNO 2] 2 2. Identify the Brønsted acids and bases in the folloing equation (A = Brønsted acid, B = Brønsted base). HPO 4 2- HSO 4 - H 2PO 4 - SO 4 2- B A B A B B A A A B A B A B B A E) B A A B 3. The equilibrium constant for the reaction A H HA is called a b 1 a b E) a 4. According to the Brønsted-Lory definition, an acid is a substance that increases the hydroxide ion concentration in a solution. a substance that increases the hydrogen ion concentration in a solution. a substance that can accept a proton from another species in solution. a substance that can donate a proton to another species. E) an electron pair acceptor.
5. Which of the folloing is a conjugate acid-base pair? HCl/OCl 3 H 3PO 4/PO 3 4 4 / 3 H 3O /OH E) Ca 2 /Ca(OH) 2 6. Which of the folloing does not represent a conjugate acid-base pair? HF and F - C 5H 5 and C 5H 5N H 3O and H 2O HCN and 3 7. The hydrogen sulfate or bisulfate ion HSO 4 can act as either an acid or a base in ater solution. In hich of the folloing equations does HSO 4 act as an acid? HSO 4 H 2O H 2SO 4 OH HSO 4 H 3O SO 3 2H 2O HSO 4 OH H 2SO 4 O 2 HSO 4 H 2O 2 SO 4 H 3O 8. The conjugate base of a eak acid is a strong base. a eak base. a strong acid. a eak acid. 9. The folloing acids are listed in order of decreasing acid strength in ater. HI > HNO 2 > CH 3COOH > HClO > HCN According to Brønsted-Lory theory, hich of the folloing ions is the eakest base? I NO 2 CH 3COO ClO E) CN 10. Given that the a for HOCl is 3.5 10-8, calculate the value for the reaction of HOCl ith OH -. 3.5 10 6 3.5 10-8 3.5 10-22 2.9 10-7 11. In deciding hich of to acids is the stronger, one must kno the concentration of each acid solution only. the ph of each acid solution only. the equilibrium constant of each acid only. all of the these. E) both the concentration and the equilibrium constant of each acid. 12. Which reaction does not proceed far to the right? HCl H 2O H 3O Cl H 3O OH 2H 2O H 2O HSO 4 H 2SO 4 OH HCN OH H 2O CN E) H 2SO 4 H 2O H 3O HSO 4
13. The acids HC 2H 3O 2 and HF are both eak, but HF is a stronger acid than HC 2H 3O 2. HCl is a strong acid. Order the folloing according to base strength. C 2H 3O 2 > F > Cl > H 2O C 2H 3O 2 > F > H 2O > Cl Cl > F > C 2H 3O 2 > H 2O F > C 2H 3O 2 > H 2O > Cl 14. At a particular temperature, the ion-product constant of ater,, is 2.4 10-14. What is the ph of pure ater at this temperature? 7.00 7.19 6.56 6.81 E) 6.62 15. Calculate [H ] in a solution that has a ph of 9.3. 5 M 9 M 5 10 10 M 2 10 5 M E) 1 10 1 M 16. Find the ph of a solution at 25ºC in hich [OH ] = 4.3 10 8 M. 7.37 6.63 8.63 3.70 E) 4.30 17. The ph of a solution is raised from 3 to 5. Which of the folloing statement is false? The poh decreases from 11 to 9. The [H ] decreases by a factor of 20. The final [OH ] (at ph = 5) is 10 9 M. The initial [H ] (at ph = 3) is 10 3 M. E) The initial solution could be 0.001 M HNO 3. 18. Solid calcium hydroxide is dissolved in ater until the ph of the solution is 10.94. What is the hydroxide ion concentration [OH ] of the solution? 1.1 10 11 M 3.06 M 8.7 10 4 M 1.0 10 14 M 19. Which of the folloing indicates the most acidic solution? [OH ] = 0.5 M [H ] = 0.3 M poh = 5.9 ph = 1.2 E) [H ] = 1.0 10 4 M 20. Calculate the ph of a 1.9 M solution of HNO 3. 0.28 0.64 0.28 14.28 E) 13.72
21. Calculate the ph of a solution made by mixing equal volumes of a solution of HCl ith a ph of 1.44 and a solution of HNO 3 ith a ph of 2.74. (Assume the volumes are additive.) 2.09 1.72 4.19 1.42 E) 2.74 22. What concentration of HF ( a = 7.2 10 4 ) has the same ph as that of 0.068 M HCl? 6.4 M 0.068 M 4.9 10 6 M 1.1 10 2 M E) 0.16 M 23. The ph of a 0.6 M solution of a eak acid is 4.0. What percent of the acid has ionized? 0.02% 2% 7% 4% E) 0.06% 24. The ph of a 0.025 M eak acid solution is 5.29. Calculate a for this acid. 1.0 10 9 5.1 10 6 1.5 10 16 2.0 10 8 E) 2.0 10 9 25. Ho many moles of benzoic acid, a monoprotic acid ith a = 6.4 10 5, must be dissolved in 500. ml of H 2O to produce a solution ith ph = 2.50? 1.6 10 1 2.0 10 2 7.8 10 2 0.50 26. Ho much ater should be added to 10.0 ml of 12.0 M HCl so that it has the same ph as 0.90 M acetic acid ( a = 1.8 10 5 )? (Assume the volumes are additive.) 30 ml 300 ml 3 L 30 L E) 300 L 27. A 0.240 M solution of the salt NaA has ph = 8.40. Calculate a for the acid HA. 6.60 10 17 1.05 10 5 3.80 10 4 2.63 10 11
28. What is the equilibrium constant for the folloing reaction? 4 OH 3 H 2O E) 1 b 3 1 a 4 a 4 b 3 b 3 29. A 2.00-g sample of NaOH(s) is added to enough ater to make 250.0 ml of solution at 25ºC. What is the ph of this solution? 0.70 14.90 12.10 13.30 E) 10.30 30. Calculate the ph of a 0.50 M 3 ( a of 4 = 5.6 10 10 ) solution. 13.72 7.00 4.78 2.52 31. The ph of a 2.1 10 3 M solution of a eak base is 9.87. Calculate b for this base. 1.2 10 4 6.4 10 8 2.6 10 6 8.7 10 18 32. The ph of a 0.120 M solution of a eak base is 10.97 at 25ºC. Calculate the ph of a 0.0316 M solution of the base at 25ºC. 2.89 10.68 10.39 11.54 E) 3.32 33. The dihydrogenphosphate ion, H 2PO 4, has both a conjugate acid and a conjugate base. These are, respectively, H 3PO 3 4 and PO 4 H 3PO 2 4 and HPO 4 H 2PO 2 4 and HPO 4 2 3 HPO 4 and PO 4 E) 2 HPO 4 and H 3PO 4 34. Which of the species belo, hen dissolved in H 2O, ill not produce a basic solution? CN NaF NaI 2CO 3 ; that is, they all ill produce a basic solution
35. If NaHCO 3 is dissolved in pure ater, ill the solution be acidic, neutral, or basic? acidic neutral basic 36. If 4CN is dissolved in pure ater, ill the solution be acidic, neutral, or basic? ( a ( 4 ) = 5.6 x 10-10, a (HCN) = 6.2 x 10-10 ) acidic neutral basic Ansers: 1. A 2. E 3. C 4. D 5. C 6. D 7. D 8. B 9. A 10. A 11. C 12. C 13. B 14. D 15. C 16. B 17. B 18. C 19. B 20. C 21. B 22. A 23. A 24. A 25. C 26. D 27. C 28. A 29. D 30. E 31. C 32. B 33. B 34. C 35. C 36. C