CHE 107 24 October 1996
Mid-Term Examination II
University of Kentucky Department of Chemistry
Mid-Term Examination II
University of Kentucky Department of Chemistry1. What is the pH of a solution made by dissolving 0.20 mol of HCl and 0.15 mol of NaOH in 1.00 L of water?
A. 0.70 B. 1.30 C. 7.00 D. 12.70
2. Which of the following curves corresponds to the titration of a weak base (i.e., analyte) with a strong acid (i.e., titrant)?
3. What is the pH at the equivalence point for the titration of 0.100 M nitrous acid (HNO2; Ka = 4.5 x 10-4) with 0.100 M KOH?
A. below 6.5 B. 7.0 C. between 7.5 and 9.5 D. above 9.5
4. Which of the following pairs of chemicals could be used to prepare a buffer solution?
A. NaCl + HCl B. NaCl + NaOH C. NaF + HF D. NaOCl + NaOH
5. A weak acid and its conjugate base can be used to prepare buffer solutions over a range of about two pH units. This pH range corresponds to an acid/base ratio range of
A. 0 to 100 B. 0.10 to 10 C. 0.010 to 100 D. -1.0 to 1.0
6. What is the pH of a solution made by dissolving 0.20 mol of propionic acid (C2H5CO2H, Ka = 1.3 x 10-5) and 0.15 mol of sodium propionate (Na+C2H5CO2-) in 1.00 L of water?
A. 0.70 B. 4.76 C. 4.89 D. 5.02
7. The indicator methyl orange is red in its acidic form and yellow in its alkaline form. Its pKIn is 3.46. For which of the titrations listed below is it most likely to be a suitable indicator? (All species are in dilute aqueous solution, approx. 0.1 M.)
A. Titration of a strong acid with a strong base. B. Titration of a weak acid with a strong base. C. Titration of a strong base with a strong acid. D. Titration of a weak base with a strong acid.
8. Thymol blue (TBH2) is a diprotic acid which is commonly used as an indicator. It is red at low pH, yellow at intermediate pH and blue at high pH. Its acid-base behavior is described by the equilibria:
TBH2 + H2O = TBH- + H3O+ Ka1 = 2.2 x 10-2 TBH- + H2O = TB2- + H3O+ Ka2 = 6.3 x 10-10
Which statement is true?
A. If most of the indicator is in the TBH2 form, the solution is blue. B. If most of the indicator is in TB2- form, the solution is red. C. At pH 7, the solution is green. D. At pH 2, the solution is orange.
9. Order the Ka values for the triprotic acid H3AsO4 from largest to smallest.
A. Ka1 > Ka2 > Ka3 B. Ka1 < Ka2 < Ka3 C. Ka1 = Ka2 = Ka3 D. Ka2 > Ka1 > Ka3
10. Consider a diprotic acid, H2A, Ka1 = 1.5 x 10-3 and Ka2 = 2.0 x 10-6. Which of the following has the highest concentration in a 1.00 M solution of H2A in water?
A. H2A(aq) B. HA-(aq) C. A2-(aq) D. H3O+(aq)
11. For H2SO4, Ka2 is about 0.012. What is the approximate [H3O+] in a 0.10 M solution of H2SO4?
A. 0.10 M B. 0.11 M C. 0.20 M D. 0.35 M
12. Which of the following is about as soluble in 0.100 M HNO3 as in pure H2O?
A. CaS B. CaBr2 C. CaCO3 D. CaF2
13. Which of the following does not have units of energy?
A. delta H B. P delta V C. delta G D. delta S
14. When the reaction
is carried out at constant temperature and pressure, which statement is true?
A. P delta V = 0. B. delta S < 0. C. delta H = the heat absorbed by the system. D. delta G = the heat transferred from the system to its surroundings.
15. Given the following delta H298o values,
calculate delta H298o for the reaction
A. -566.0 kJ B. -504.0 kJ C. +283.0 kJ D. -283.0 kJ
16. Which of the following statements is true?
A. Standard enthalpies of formation of compounds can be positive, negative or zero. B. "Standard heat of formation" is a synonym for "free energy of formation." C. delta H for the reaction
defines delta Hfo of CH4(g). D. The standard enthalpy of formation of N2(g) is greater than zero.
17. For which of the following is delta Hfo not zero?
A. N2(g) B. O2(g) C. C(graphite) D. H(g)
18. Which of the following has the greatest entropy?
A. H2O(s, 200 K) B. H2O(s, 273 K) C. H2O(l, 273 K) D. H2O(g, 350 K)
19. Which of the following processes has delta S > 0?
A. 2 O3(g) ---> 3 O2(g)
B. Ni(s) + 4 CO(g) ---> Ni(CO)4(g)
C. Hg(l) ---> Hg(s)
D. Ag+(aq) + Cl -(aq) ---> AgCl(s)
20. Calculate the standard entropy change when one mole of C2H5OH (ethanol) vapor is formed from the liquid at 25oC.
Substance delta Ho (kJ mol-1) delta S (J K-1 mol-1) delta G (kJ mol-1) C2H5OH (g) -278 161 -175 C2H5OH (g) -235 283 -169
A. 122 J K-1 B. 43 kJ C. -43 kJ D. 6 J K-1
21. Use the following data to estimate the normal boiling point of CH3OH (methanol).
delta Hvapo (CH3OH) = 38.0 kJ mol-1 delta Svapo (CH3OH) = 112.9 J K-1 mol-1
A. 74.9 K B. 337 K C. 436 K D. 2971 K
22. Which equation correctly describes all systems that are at equilibrium?
A. delta Ho = -T delta So B. delta G = 0 C. delta Go = RT ln Keq D. delta Suniverse > 0
23. delta Go = -27 kJ for the reaction
At 298 K, which set of conditions will make this reaction the most strongly spontaneous (that is, will lead to the most negative delta G)?
[NH4+] (M, aq) [NH3] (M, aq) pH A. 1.0 1.0 14 B. 1.0 1.0 2 C. 0.10 0.10 7 D. 0.10 0.10 12
24. A reaction that has delta Ho < 0 and delta So < 0 at 298 K is most likely to be
A. spontaneous at all temperatures. B. spontaneous at low temperatures but not at very high temperatures. C. spontaneous at high temperatures but not at very low temperatures. D. non-spontaneous at all temperatures.
25. For a certain reaction, delta G = -4.31 kJ at 400 K. What is Kp of this reaction at 400 K?
A. 0.27 B. 1.0 C. 3.6 D. 19