1 CH302 Exam 4 Practice Problems (buffers, titrations, Ksp) Equilibrium Constants The following equilibrium constants will be useful for some of the problems. Substance Constant Substance Constant HCO 2 H K a = 1.8 10-4 H 2 CO 3 K 1 = 4.2 10-7 HNO 2 K a = 4.5 10-4 K 2 = 4.8 10-11 HOCl K a = 3.5 10-8 (COOH) 2 K 1 = 5.9 10-2 HF K a = 7.2 10-4 K 2 = 6.4 10-5 HCN K a = 4.0 10-10 CH 3 COOH K a = 1.8 10-5 H 2 SO 4 K 1 = very large C 6 H 5 NH 2 K b = 4.2 10-10 K 2 = 1.2 10-2 NH 3 K b = 1.8 10-5 HOBr K a = 2.5 10-9 1.Refer to Equilibrium Constants. The nonionized form of an acid indicator is yellow, and its anion is blue. The K a of this indicator is 10-6. What will be the approximate ph range over which this indicator changes color? a. 3-5 d. 8-10 b. 4-6 e. 9-11 c. 5-7 2.Refer to Equilibrium Constants. The equivalence point of the titration of an unknown base with HCl is at ph = 5.90. What would be the K a for the best choice of an indicator for this titration? a. 10-2 d. 10-6 b. 10-4 e. 10-7 c. 10-8 3.Refer to Equilibrium Constants. What is the ph at the point in a titration at which 20.00 ml of 1.000 M KOH has been added to 25.00 ml of 1.000 M HBr? a. 1.67 d. 2.71 b. 0.95 e. 1.22 c. 3.84 4.Refer to Equilibrium Constants. Which titration curve could describe the titration of a solution of HCl by addition of a solution of KOH? a. b. c.
2 d. e. 5.Refer to Equilibrium Constants. Which indicator could be used to titrate aqueous NH 3 with HCl solution? Acid Range Color ph Range Basic Range Color a. pink 1.2-2.8 yellow b. blue 3.4-4.6 yellow c. yellow 6.5-7.8 purple d. colorless 8.3-9.9 red e. none of these indicators 6.Refer to Equilibrium Constants. Calculate the ph of a solution prepared by adding 60.0 ml of 0.100 M NaOH to 100. ml of 0.100 M CH 3 COOH solution. a. 4.56 d. 5.08 b. 4.92 e. 5.16 c. 5.00 7.Refer to Equilibrium Constants. Calculate the ph of a solution resulting from the addition of 50.0 ml of 0.30 M HNO 3 to 50.0 ml of 0.30 M NH 3. a. 4.92 d. 5.04 b. 7.46 e. 8.30 c. 6.18 8.Refer to Equilibrium Constants. Which of the following titrations could the following curve describe? a. NaOH added to HF d. KOH added to HClO 4 b. HCl added to aqueous NH 3 e. HNO 3 added to NaOH c. CH 3 COOH added to aqueous NH 3 9.Refer to Equilibrium Constants. When a weak base is titrated with a strong acid, the ph at the equivalence point is always. a. 7 b. < 7 c. > 7 d. < 1 e. > 4 10.. Refer to Equilibrium Constants. Consider the titration of a solution of a weak acid by adding a solution of a strong base. Which response includes all the following statements that are true, and no others?
3 a. The end-point cannot be detected using an indicator. b. The ph at the equivalence point is 7.00. c. The solution is buffered before the equivalence point. d. The solution is buffered both before and after the equivalence point. e. Methyl orange (ph color range 3.1-4.4) would be a better indicator for this titration than would thymol blue (ph range 8.0-9.6). 11.Which of the following solubility product expressions is incorrect? a. = [Ag + ] 2 [S 2- ] b. = [Ca 2+ ][F - ] 2 c. = [Sb 2+ ] 3 [S 3- ] 2 d. = [Cu 2+ ][S 2- ] e. = [Ag + ] 3 [PO 3-4 ] 12.How is the K sp of Ca 3 (PO 4 ) 2 related to s, the molar solubility of Ca 3 (PO 4 ) 2? a. K sp = 4s 5 d. K sp = 54s 4 b. K sp = 27s 3 e. K sp = 108s 5 c. K sp = 18s 5 13.Calculate the solubility product constant for aluminum hydroxide. Its molar solubility is 2.9 10-9 mole per liter at 25 C. a. 9.8 10-26 d. 2.1 10-34 b. 4.9 10-26 e. 1.9 10-33 c. 7.1 10-35 14.The solubility of Fe(OH) 2 is 3.00 10-3 g in 2.00 liters at 18 C. What is its K sp at 18 C? a. 4.92 10-12 d. 1.86 10-14 b. 6.03 10-9 e. 2.11 10-11 c. 2.44 10-10 15.The solubility of cobalt(iii) hydroxide is 54 pg/100. ml of water at 25 C. Calculate the K sp for cobalt(iii) hydroxide at 25 C. a. 5.8 10-46 d. 5.8 10-50 b. 1.7 10-45 e. 1.6 10-48 c. 1.6 10-44 16.The K sp for magnesium arsenate is 2.1 10-20 at 25 C. What is the molar solubility of Mg 3 (AsO 4 ) 2 at 25 C? a. 6.7 10-3 M d. 7.0 10-5 M b. 3.6 10-4 M e. 1.4 10-6 M c. 4.5 10-5 M 17.Calculate the concentration of OH - ions in a saturated Mn(OH) 2 solution. The solubility product for Mn(OH) 2 is 4.6 10-14. a. 1.0 10-5 M d. 3.2 10-5 M b. 2.0 10-5 M e. 4.5 10-5 M c. 1.6 10-5 M 18.Calculate the ph in a saturated Mn(OH) 2 solution. The solubility product for Mn(OH) 2 is 4.6 10-14. a. 9.0 d. 9.5 b. 9.2 e. 9.7 c. 9.3 19.Calculate the concentration of F - ions in saturated CaF 2 solution at 25 C. K sp = 3.9 10-11. a. 2.1 10-4 M d. 0.032 M b. 4.3 10-4 M e. 0.10 M c. 0.016 M 20.What mass of Zn(OH) 2 is contained in 1.0 liter of saturated solution? K sp = 4.5 10-17.
a. 0.00011 g d. 0.010 g b. 0.00022 g e. 0.016 g c. 0.00044 g 21.The solubility product constant for MgF 2 is 6.4 10-9. How many grams of MgF 2 will dissolve in 150 ml of H 2 O at 25 C? a. 1.1 10-2 g d. 6.0 10-4 g b. 5.8 10-3 g e. 2.2 10-3 g c. 4.7 10-1 g 22.What concentration of aqueous NH 3 is necessary to just start precipitation of Mn(OH) 2 from a 0.020 M solution MnSO 4? K b for NH 3 is 1.8 10-5 and K sp for Mn(OH) 2 is 4.6 10-14. a. 1.4 10-5 M b. 3.7 10-7 M c. 1.6 10-6 M d. 1.3 10-7 M e. 8.4 10-2 M 23.If 1.0 liter of solution is to be made 0.010 M in Mg(NO 3 ) 2 and 0.10 M in aqueous ammonia, how many moles of NH 4 Cl are necessary to prevent the precipitation of magnesium hydroxide? The solubility product for Mg(OH) 2 is 1.5 10-11, and the ionization constant for aqueous ammonia is 1.8 10-5. a. 0.018 mol b. 0.016 mol c. 0.020 mol d. 0.040 mol e. 0.046 mol 4
CH302 Exam 4 Practice Problems (buffers, titrations, Ksp) Answer Section 5 MULTIPLE CHOICE 1. ANS: C PTS: 1 TOP: Acid-Base Indicators 2. ANS: D PTS: 1 TOP: Acid-Base Indicators 3. ANS: B PTS: 1 TOP: Strong Acid/Strong Base Titration Curves 4. ANS: B PTS: 1 TOP: Strong Acid/Strong Base Titration Curves 5. ANS: B PTS: 1 6. ANS: B PTS: 1 7. ANS: D PTS: 1 8. ANS: B PTS: 1 9. ANS: B PTS: 1 10. ANS: C PTS: 1 11. ANS: C PTS: 1 TOP: Solubility Product Constants 12. ANS: E PTS: 1 TOP: Determination of Solubility Product Constants 13. ANS: E PTS: 1 TOP: Determination of Solubility Product Constants 14. ANS: D PTS: 1 TOP: Determination of Solubility Product Constants 15. ANS: C PTS: 1 TOP: Determination of Solubility Product Constants 16. ANS: C PTS: 1 TOP: Uses of Solubility Product Constants 17. ANS: E PTS: 1 TOP: Uses of Solubility Product Constants 18. ANS: E PTS: 1 TOP: Uses of Solubility Product Constants 19. ANS: B PTS: 1 TOP: Uses of Solubility Product Constants 20. ANS: B PTS: 1 TOP: Uses of Solubility Product Constants 21. ANS: A PTS: 1 TOP: Uses of Solubility Product Constants 22. ANS: D PTS: 1 TOP: Simultaneous Equilibria Involving Slightly Soluble Compounds 23. ANS: E PTS: 1 TOP: Simultaneous Equilibria Involving Slightly Soluble Compounds