26 March 1996
CHE 107 29 February 1996 Mid-Term Examination II
University of Kentucky Department of Chemistry
1. How many milliliters of 0.0750 M HCl are needed to titrate 27.0 mL of 0.0600 M Ba(OH)2 solution to the equivalence point?A. 21.6 mL B. 10.8 mL C. 43.2 mL D. 12.2 mL
2. The titration of a 20.0 g sample of vinegar required 37.5 mL of 0.400 M NaOH to reach the equivalence point. Determine the % by weight concentration of acetic acid in the vinegar. (Molar mass of acetic acid = 60.0 g/mol)A. 4.50% B. 0.0150% C. 15.0% D. 5.42%
3. In the titration of a weak acid with a strong base,A. the equivalence point occurs at a pH less than 7. B. the equivalence point occurs at a pH greater than 7. C. the equivalence point occurs at a pH near 2. D. the equivalence point occurs at a pH of 7.
4. What is the pH of the solution that results when 50.0 mL of 0.20 M NH3(aq) is mixed with 25.0 mL of 0.10 M HCl(aq)? (Kb for NH3 = 1.8 x 10-5)A. 9.73 B. 4.27 C. 11.28 D. 8.78
5. Which of these aqueous solutions are buffers?1. A solution that is 0.1 M HNO3 and 0.1 M HCl. 2. A solution that is 0.1 M NaH2PO4 and 0.1 M Na2HPO4. 3. A solution made by mixing 10. mL of 0.1 M HF and 5.0 mL of 0.1 M NaOH. 4. A solution made by mixing 10. mL of 0.1 M KOH and 20. mL of 0.1 M HCl.
A. 1 and 2 B. 2 and 3 C. 3 and 4 D. 1 and 4
6. Calculate the pH of a solution formed by adding 25.0 mL of 0.10 M HCl to 25.0 mL of 0.10 M NH3 (Kb = 1.80 x 10-5 for NH3).A. 10.72 B. 7.00 C. 3.02 D. 5.28
7. How many grams of sodium acetate must be added to 200. mL of a 0.500 M acetic acid solution to prepare a buffer with pH = 4.35? (Acetic acid Ka = 1.80 x 10-5; molar mass of sodium acetate = 82.0 g/mole)A. 3.30 g B. 0.201 g C. 20.4 g D. 16.5 g
8. What is the pH of the solution formed when 20.0 mL of 0.250 M formic acid is mixed with 20.0 mL of 0.500 M sodium hydroxide? (Ka of formic acid = 1.80 x 10-4)A. 2.17 B. 13.10 C. 12.13 D. 0.90
9. Calculate the molar concentrations of H3O+, HSO4-, and SO42- in a 0.250 M solution of H2SO4. Assume Ka1 is very large; Ka2 = 1.20 x 10-2.[H3O+], M [HSO4-], M [SO42-], M A. 0.250 0.250 0.000 B. 0.250 0.250 0.0120 C. 0.500 0.000 0.500 D. 0.261 0.239 0.0110
10. Calculate Kb for the carbonate ion, CO32-, if Ka1 = 4.3 x 10-7 and Ka2 = 5.6 x 10-11 for carbonic acid, H2CO3.A. 1.0 x 10-14 B. 5.6 x 10-11 C. 1.8 x 10-4 D. 2.3 x 10-8
11. Select those substances that are amphoteric from the following list.
B(OH)3, NaHCO3, Al(OH)3, Na3PO4 A. Both B(OH)3 and Al(OH)3 B. Only Al(OH)3 C. Both NaHCO3 and Na3PO4 D. Both NaHCO3 and Al(OH)3
12. Specify if addition of the second substance in each of the following increases (I) or decreases (D) the solubility of the first substance.
1. Al(OH)3, NaOH; 2. PbCl2, Pb(NO3)2; 3. CuSO4, NH3 A. 1-D, 2-I, 3-I B. 1-I, 2-I, 3-D C. 1-I, 2-D, 3-I D. 1-D, 2-D, 3-I
13. Which one of the following salts will be substantially more soluble in acidic solution than in pure water?A. PbF2 B. AuCl3 C. CuBr D. AgNO3
14. What is delta Ho at 25oC for the following reaction if delta Eo = -5151.9 kJ/mol for the reaction, also at 25oC?
C10H8(s) + 12 O2(g) ---> 10 CO2(g) + 4 H2O(l) A. - 5158.1 kJ/mol B. - 5156.9 kJ/mol C. - 5146.9 kJ/mol D. - 5154.4 kJ/mol
15. Which of the following are path dependent (i.e., are not state functions)? 1. Entropy. 2. Amount of work done by system. 3. The Gibbs free energy. 4. Heat flow into the system.A. 2 and 4 B. 1 and 3 C. 2 and 3 D. 3 and 4
16. Of the species listed below, which one has a standard enthalpy of formation of zero?A. H2O(l) B. C(diamond) C. Na(g) D. Br2(l)
17. The delta Ho of which one of the following chemical equations would be the standard heat of formation of C6H3N3O7 (picric acid)?A. C6H3N3O7(s) --> 11/2 CO(g) + 3/2 H2O(g) + 3/2 N2(g) + 1/2 C(graphite) B. 12 C(graphite) + 3 H2(g) + 3 N2(g) + 7 O2(g) --> 2 C6H3N3O7(s) C. 6 C(graphite) + 3 H(g) + 3 N(g) + 7 O(g) --> C6H3N3O7(s) D. 6 C(graphite) + 3/2 H2(g) + 3/2 N2(g) + 7/2 O2(g) --> C6H3N3O7(s)
18. Use the standard enthalpies of formation provided below to calculate the enthalpy change for the reaction
AlCl3(s) + 3 H2O(l) --> Al(OH)3(s) + 3 HCl(g) at 298 K and 1 atm.
Substance delta H (kJ/mol) AlCl3(s) - 704.2 Al(OH)3(s) - 1287.0 H2O(l) - 285.8 H2O(g) - 241.8 HCl(g) - 92.3
A. - 134.3 kJ B. + 134.3 kJ C. - 2.3 kJ D. + 91.4 kJ
19. For which of the following reactions are the entropy changes greater than zero? Assume that the reactions take place at 298 K and all reactants and products are in their standard states.1. CO(g) + 2 H2(g) --> CH3OH(l) 2. C(s) + H2O(g) --> CO(g) + H2(g) 3. NaCl(s) --> Na+(aq) + Cl-(aq) 4. 3 H2(g) + N2(g) --> 2 NH3(g)
A. 1 and 2 B. 1 and 3 C. 2 and 3 D. 1 and 4
20. For which of the following are the signs of the entropy change positive? 1. hydrogen and oxygen combine to form water. 2. water evaporates. 3. wood is burned to provide heat. 4. water freezes.A. 1 and 2 B. 2 and 3 C. 1 and 4 D. 1 and 3
21. Which one of the following is equal to delta H at equilibrium?A. delta E B. delta G C. P delta V D. T delta S
22. For the reaction
PCl3(g) + Cl2(g) --> PCl5(g) delta Go = - 37.2 kJ at 25oC. The gases are placed in a reaction vessel at 25oC with PCl3 at 0.200 atm, Cl2 at 0.500 atm, and PCl5 at 0.200 atm. Calculate delta G at 25oC, and state whether the reaction proceeds from left to right (L ---> R), right to left (R ---> L), or is at equilibrium.
A. 0, at equilibrium B. - 35.5 kJ, L ---> R C. + 35.5 kJ, R ---> L D. delta G = 71.0 kJ, R ---> L
23. For a certain process, delta H = 178. kJ and delta S = 160. J/K. What is the minimum temperature at which the process will be spontaneous? (Assume delta H and delta S do not vary with temperature).A. 1110 K B. 839 K C. 273 K D. 1.110 K
24. Given that Ka for benzoic acid at 298 K is 6.5 x 10-5. Calculate delta Go for its dissociation in aqueous solution, and select the value of delta G at equilibrium.A. + 23.9 kJ, 0 B. + 23.9 kJ, - 23.9 kJ C. + 10.4 kJ, 0 D. - 23.9 kJ, + 23.9 kJ
25. Given the following data, referred to 25oC, compute delta Go and Kp for the reaction N2(g) + 3 H2(g) --> 2 NH3(g) at 298.15 K.delta Hfo(kJ mol-1) So (J mol-1 K-1) N2(g) 0 191.61 H2(g) 0 130.68 NH3(g) - 46.11 192.45
A. delta Go = 59.17 kJ, Kp = 4.31 x 10-11 B. delta Go = - 32.96 kJ, Kp = 1.68 x 10-6 C. delta Go = - 32.96 kJ, Kp = 5.95 x 105 D. delta Go = - 59.17 kJ, Kp = 2.32 x 1010