Practice Test - Chapter 13, 14, 15

Practice Test - Chapter 13, 14, 15 1. For which of the following values of the equilibrium constant does the reaction go the farthest to completion? a. 10 5 b. 10 3 c. 10 0 d. 10-3 e. 10-5 2. Carbon disulfide and chlorine react according to the following equation: CS 2 + 3Cl 2 S 2 Cl 2 + CCl 4 When 1.00 mol of CS 2 and 3.00 mol of Cl 2 are placed in a 2.00-L container and allowed to come to equilibrium, the mixture is found to contain 0.250 mol of CCl 4. What is the amount of Cl 2 at equilibrium? a. 2.25 mol b. 2.75 mol c. 0.75 mol d. 0.25 mol e. 0.50 mol 3. N 2 4 2N 2 At 25 o C and 1 atm of pressure, 1 mol of N 2 4 forms an equilibrium mixture with N 2. At equilibrium there are 0.815 mol N 2 4 and 0.370 mol N 2. At 55 o C and 1 atm of pressure, 1 mol of N 2 4 forms an equilibrium mixture containing 0.50 mol N 2 4 and 1.0 mol N 2. Therefore, we can conclude that a. N 2 molecules are colliding with each other more frequently at 25 o C than at 55 o C. b. The reaction above is exothermic. c. N 2 reacts faster at 25 o C than at 55 o C. d. The equilibrium constant for the reaction above will increase with temperature. e. Heat is evolved when N 2 4 goes to N 2. 4. When phosphorous pentachloride is made by the reaction of PCl 3 and Cl 2 at 240 o C, K c = 20. PCl 3 + Cl 2 PCl 5 If pure PCl 5 is placed in a 1.00-L container and allowed to come to equilibrium and the equilibrium concentration of PCl 5 is 0.050 mol/l, then the concentration of PCl 3 is a. 0.025M b. 0.050 M c. 0.100 M d. 0.200 M e. 0.300 M

5. Carbon tetrachloride reacts with oxygen at high temperatures to produce chlorine and carbonyl chloride. 2CCl 4 + 2 2CCl 2 + 2Cl 2 K c = 1.9x10 19 What is the K c for the following: a. 5.3 x 10-20 b. 2.3 x 10-10 c. 4.4 x 10 9 d. 1.9 x 10 19 e. 1.9 x 10 19 6. Given the equilibrium constants for the following reactions 4Cu(s) + 2 2Cu 2 (s),k 1 2Cu(s) Cu 2 (s) + 1 2 2,K 2 what is K for the system 2Cu(s) + 2 a. K 1 x K 2 b. K 1 1/2 x K 2 c. K 1 1/2 /K 2 d. K 2 1/2 /K 1 e. K 1 x K 2 1/2 2CCl 2 + 2Cl 2 2CCl 4 + 2 2Cu(s) equivalent to? 7. Suppose equilibrium is established by adding 0.20 mol N and 0.30 mol F 2 to a 5.0-L container using the equation 2N + 3F 2 2F 3 N. If y moles of F 3 N are present at equilibrium, then the number of moles of fluorine remaining at equilibrium will be a. 0.30 y. b. 0.20 y. c. 0.30 3/2y. d. 0.30 2y. e. 0.06 0.20y. 8. Under the conditions in Question 7, the equilibrium concentration of N will be a. 0.20 y. b. 0.20 2y. c. 0.04 0.20y. d. 0.05 0.50y. e. 0.20y. 9. Which of the following equilibria would be affected by volume changes at constant temperature? 1. 2N + 3F 2 2F 3 N 2. BF 3 + N NBF 3 (s) 3. 3 + N N 2 + 2 d. 1 and 2 only e. 1, 2, and 3

10. For a specific reaction, which of the following statements can be made about the equilibrium constant? a. It always remains the same. b. It increases when the concentration of one of the products is increased. c. It changes with changes in the temperature. d. It increases when the concentration of one of the reactants is increased. e. It can be changed by the addition of a catalyst. 11. For each reaction system 2N N 2 + 3H 2 at equilibrium, H is 92kJ. In order to increase the value of K for this reaction, we could 1. increase the temperature 2. decrease the temperature 3. increase the pressure 4. decrease the pressure c. 1 and 3 only d. 2 and 3 only e. 2 and 4 only 12. For the following reaction system at equilibrium, which one of the changes would cause a shift to the right? 2NBr 2N + Br 2 H = 30kJ a. Decrease the volume of the reaction vessel. b. Add some N. c. Remove some NBr. d. Add Br 2. e. Increase the temperature. 13. Consider the equilibrium PCl 3 + Cl 2 PCl 5 H = 92kJ The concentration of PCl 3 at equilibrium will be increased by a. decreasing the volume / increasing the pressure b. adding Cl 2 to the system. c. decreasing the temperature. d. the addition of neon. e. the addition of PCl 5. 14. Which of the following is the conjugate base of H 2 P 4 1- a. 1- H 2 P 4 b. 2- HP 4 c. 3- P 4 d. P 4 e. two of the above

15. Solid Hg, liquid Hg, and gaseous 2 are placed in a glass bulb and are allowed to reach equilibrium at a given temperature. 2Hg(s) + heat 2Hg(l) + 2 The amount of Hg(l) in the bulb could be decreased by 1. removing some Hg. 2. removing some 2. 3. decreasing the temperature. d. 1 and 2 only e. 2 and 3 only 16. Each of the following pairs contains one strong acid and one weak acid except a. HN 3 and H 2 C 3. b. HF and HCl. c. H 2 S 4 and H 2 S. d. HCl and HC 2 2. e. HBr and P 4. 17. What is the net ionic equation for the acid-base reaction that occurs when acetic acid and potassium hydroxide solutions are mixed? a. H + + H H 2 b. + + H 2H 2 c. HC 2 2 + KH KC 2 2 d. C 2 2 + H + + K + + H K + + C 2 2 e. HC 2 2 + H C 2 2 18. All the following can function as Lewis acids except a. NH 4 +. b. H +. c. BF 3. d. BeCl 2. e. Ag +. 19. The acid strength decreases in the series HBr > HS 4 - > C CH > HCN > HC 3 -. The weakest base is a. C 3 2- b. CN - c. C C - d. S 4 2- e. Br - 20. For a given weak acid, HA, the value of Ka a. will change with the ph. b. will change with the ph. c. will change with temperature. d. cannot be less than 10-7. e. cannot be greater than 10-7.

21. The ph of 0.1 M N is approximately a. 1. b. 3. c. 7. d. 11. e. 13. 22. A solution that is formed by combining 300. ml of 0.10 M Ba(H) 2 with 200. ml of 0.30 M HCl has a + concentration of. Ba(H) 2 (aq) + 2HCl(aq) BaCl 2 (aq) + 2H 2 a. 0.060 M b. 0.030 M c. 0.15 M d. 1.0 x 10-7 M e. 1.7 x 10-13 M 23. The ionization constant of water at 45 o C is 4.0 x 10-14. What is the ph of pure water at this temperature? H 2 H + (aq) + H (aq) a. 5.70 b. 6.70 c. 7.00 d. 7.70 e. 13.40 24. The hydronium-ion concentration of a 0.010 M acetic acid solution is 4 x 10-4 M. The ph of the solution is a. 2.0 b. 3.4 c. 4.0 d. 4.2 e. 4.7 25. Which one of the following mixtures is suitable for making buffers? 1. P 4 and NaH 2 P 4 2. Na 2 C 3 and NaHC 3 3. NH 4 Cl and N d. 1 and 2 only e. 1, 2, and 3 26. Which of the following is the most effective buffer system for a ph value of 7.45? a. H 2 C 3 /HC - 3 (K 1 = 4.4 x 10-7 ) b. HC - 3 /C 2-3 (K 2 = 4.7 x 10-11 ) c. H 2 S/HS - (K 1 = 1.0 x 10-7 ) d. HC 2-2- 4 /C 2 4 (K 2 = 5.0 x 10-5 ) e. H 2 P - 4 /HP 2-4 (K 2 = 6.3 x 10-8 )

27. Which of the following salt solutions is basic? a. NH 4 Cl b. KI c. CaBr 2 d. Na 2 C 3 e. K 2 S 4 28. Which of the following reactions represent(s) the amphoteric behavior of aluminum? 1. 2Al(s) +6H + (aq) 2Al 3+ (aq) + 3H 2 2. 2Al(s) +Fe 2 3 (s) Al 2 3 (s) + 2Fe(s) 3. 2Al(s) +2H (aq) + 6H 2 2Al(H) 4 (aq) + 3H 2 d. 1 and 3 only e. 1, 2, and 3 29. The hydronium-ion concentration of a 0.050 M lactic acid solution is 2.62 x 10-3. The acid dissociation constant is 1.37 x 10-4. The ph of this lactic acid solution is a. 0.42 b. 1.30 c. 2.58 d. 3.86 e. 5.94 30. Which of the following statements is true of titration of a weak monoprotic acid by a strong base such as sodium hydroxide? a. At the equivalence point, the ph is 7. b. The moles of acid are greater than the moles of base at the equivalence point. c. The moles of base are greater than the moles of acid at the equivalence point. d. The moles of acid equal the moles of base at the equivalence point. e. The solution is acidic at the equivalence point. 31. Which of the following solutes dissolved in 1.0 kg of water would be expected to provide the fewest particles and freeze at the highest temperature? a. 0.10 mol HCl 4 b. 0.10 mol HCl 3 c. 0.10 mol HCl 2 d. 0.10 mol HCl e. 0.10 mol HCl 32. A 0.10 M solution of a weak monoprotic acid has a ph of 3.70. What is the equilibrium constant, K a, for this acid? a. 2.0 x 10-3 b. 2.0 x 10-4 c. 4.0 x 10-7 d. 4.0 x 10-8 e. 2.0 x 10-9

33. A solution that is formed by combining 300 ml of 0.020 molar NaH with 700 ml of 0.010 molar HCl has a ph of a. 1.0 b. 2.0 c. 3.0 d. 5.0 e. 7.0 34. The symbol K b (HC 3 - ) is the equilibrium constant for which reaction? a. HC 3 + H C 2 3 b. HC 2 3 C 3 + + c. HC 3 + + H 2 C 3 d. HC 3 H 2 C 3 + H e. H 2 C 3 HC 3 + + 35. Which of the following can we determine by using an equilibrium constant for a reaction? 1. the time required to reach the equilibrium 2. the extent of a reaction at equilibrium 3. the direction of a reaction upon adding both reactants and products d. 1 and 2 only e. 2 and 3 only 36. Using the equilibrium constants at 25 o C from the table, K HCN(aq) H + (aq) + CN (aq) 4.9 x 10-10 H 2 (l) H + (aq) + H (aq) 1.0 x 10-14 Calculate the value of K at 25 o C for the following reaction: a. 4.9 x 10 4 b. 2.0 x 10-4 c. 2.0 x 10-5 d. 4.9 x 10-24 e. 2.0 x 10-25 HCN(aq) + H (aq) CN (aq) (l) 37. Given the Ka of Nitrous Acid as 4.0 x 10-4, calculate the Kb of the nitrite ion. a. 4.0 x 10-4 b. 2.5 x 10-4 c. 2.5 x 10-11 d. 2.5 x 10-10 e. 4.0 x 10 10

38. Write the net ionic equation for two of the four choices below. Please note that all four reactions occur and therefore writing no reaction (NR) will be no credit. (10 pts 2pts for reactants, 3 pts for products). a. Excess potassium hydroxide solution is added to a solution of potassium dihydrogen phosphate. b. Hydrogen sulfide gas is bubbled through excess potassium hydroxide solution. c. Sulfur trioxide gas is added to water. d. Equal volumes of 0.1 M sulfuric acid and 0.1 M potassium hydroxide are mixed. You may use your calculator for the remainder of the test. Please show all work, equations, formulas, logic, and number set-ups so partial credit can be awarded. 39. Find the ph of a 0.20 M aqueous solution of the following. For HS -, K a = 1 x 10-13. (5 pts each) a. HN 3 b. K 2 S 40. A buffer solution is prepared using 400.0 ml of a 0.100 M acetic acid, HC 2 2, and 3.28 g of the soluble salt, NaC 2 2. For HC 2 2, K a = 1.74 x 10-5 a. Calculate the ph of the buffer solution. (5 pts) b. 8.0 ml of a 0.5 M NaH solution is added to the buffer. What is the new ph value of the buffered solution? (5 pts) 41. In an experiment, a 20.0 ml sample of 0.0250 M N was placed into a flask and titrated to the equivalence point and beyond using 0.0120 M HCl. K b for N = 1.74 x 10-5 (5 pts for each part below) a. Determine the volume of 0.0125 M HCl that was required to reach the equivalence point. (Be sure to show work/logic to earn 5 pts total). b. Determine the ph of the solution in the flask after a total of 20.0 ml of the 0.0125 M HCl has been added. c. Determine the ph of the solution in the flask after a total of 50.0 ml of 0.0125 M HCl was added. 42. At a given temperature, an equilibrium mixture of the reaction: 2N + 2 2N 2 contains 0.090 mol N, 0.120 mol 2 and 0.060 mol N 2 in a 3.00 L container. Calculate the K c. 43. At a given temperature the reaction CS 2 + 3Cl 2 CCl 4 + S 2 Cl 2 is at equilibrium when [CS 2 ] = 0.050 M, [Cl 2 ] = 0.25 M, [CCl 4 ] = 0.15 M, [S 2 Cl 2 ] = 0.350 M. a. Calculate the K c. b. What would be the direction of the reaction when the reactants and products have the following concentrations: [CS 2 ] = 0.15 M, [Cl 2 ] = 0.20 M, [CCl 4 ] = 0.30 M, [S 2 Cl 2 ] = 0.28 M. (Show all work for full credit). 44. Phosgene, CCl 2, is a toxic gas used in the manufacture of urethane plastics. The gas dissociates at high temperatures. CCl 2 C + Cl 2 At 400 o C, the equilibrium constant K c is 8.05 x 10-4. Find the percentage of phosgene that dissociates at this temperature when 1.00 mol of phosgene is placed in a 25.0 L vessel. 45. Aniline, a weak base, reacts with water according to the reaction represented below: C 6 H 5 NH 2 (aq) +H 2 (l) C 6 H 5 NH + 3 (aq) + H (aq) a. Write the equilibrium constant expressions, K b, for the reaction represented above. b. A sample of aniline is dissolved in water to produce 25.0 ml of a 0.10 M solution. The ph of the solution is 8.82. Calculate the equilibrium constant, K b, for this reaction.

c. The solution prepared in part (b) is titrated with 0.10 M HCl. Calculate the ph of the solution when 5.0 ml of the acid has been added. d. Calculate the ph at the equivalence point of the titration consider the information given in part (c). e. The pk a values for several indicators are given below. Which of the indicators listed is most suited for this titration? Justify your answer. Indicator pk a Erythrosine 3 Litmus 7 Thymolphthalein 10 Chapter 14, 15, 16 Practice Test Answers 1. A 19. E 2. A 20. C 3. D 21. D 4. B 22. D 5. A 23. B 6. C 24. B 7. C 25. E 8. C 26. E 9. D 27. D 10. C 28. D 11. A 29. C 12. E 30. D 13. E 31. D 14. B 32. C 15. C 33. C 16. B 34. D 17. E 35. E 18. A 36. A 37. D