Houston Community College System
Chemistry 1412
Exam # 2
Fall 2013
CHEM 1412 Exam #2
Summer 2011
Name: ____________________________
Score:
PART I - ( 3 points each) - Please write your correct answer next to each question number.
____1. What is the conjugate base of H2PO4-?
A. HPO4–2
B. H3PO4
C. PO4-3
D. OH-
____2. Which of these species will have the lowest entropy (S°)?
A. N2(g) at 298 K, 1atm
C. N2(g) at 398 K, 1atm
B. N2(g) at 298 K, 2atm
D. N2(g) at 398 K, 2atm
_____3. Which of these species will have the highest entropy?
A. I2(g)
B. I2(s)
C. Cl2(g)
D. F2(g)
____4. The average pH of coffee is 5. What is the hydroxide ion concentration?
A. 10-5M
B. 9
C. 10-9M
D. 10-19M
____5. Which of the following aqueous salt solutions will be likely to be acidic?
A. Ca(C2H3O2)2
B. CaI2
C. CsBr
D. CuBr2
C. 12
D. 4.61
C. 3.1
D. 6.9
C. 2.7
D. 11.3
C. 8.0
D. 6.0
____6. What is the pH of 0.010 M HClO4 (aq)?
A. 0.010
B. 2.0
____7. What is the pH of 0.010 M Benzoic acid (Ka = 6.28 x 10-5)?
A. 2.0
B. 4.6
_____8. What is the pH of 0.0020 M Sr(OH)2?
A. 11.6
B. 2.4
_____9. What is the pH of 0.0020 M aniline (Kb = 4.3 x 10-10)?
A. 11.3
B. 2.7
_____10. The percentage ionization of a 0.20 M weak acid is 0.038%. What is the pH of the acid?
A. 2.1
B. 4.1
C. 1.4
D. 0.70
_____11. Which of the following do you predict to be the weakest acid?
A. HIO3
6
B. HBrO3
C. HBrO4
D. HIO4
_____12. Which response includes all of the following processes that are accompanied by a increase in
entropy?
1) 3O2(g)  2O3(g)
3) 2Mg(s) +O2(g)  2MgO(s)
A. 1,2
2) 2C2H6(g) + 7O2(g)  4CO2(g) + 6H2O(g)
4) CaCl2(aq)  Ca+2(aq) + 2Cl-(aq)
B. 1, 3
C. 3,4
D. 2,4
____13. Calculate the entropy change (J?K) of the reaction. The molar entropies [So] are given in
brackets after each substance.
Al2O3(s) [51 J/K-mol] + 3 H2(g) [131 J/K/mol] 2 Al(s) [28 J/K-mol] + 3 H2O(g) [189 J/mol-K]
A. 179J/K
B. -179 J/K
C. 35 J/mol-K
D. -35 J/mol-K
C. Hg(s)
D. I2(s)
____14. Which of the following has Gf°=0 & Hf°=0?
A. CO2(g)
B. Ne2(g)
____15. Which one of the following is not a buffer solution?
A. 1.0 M HF and 1.0 CaF2
C. 1.0 M NH3 and 1.0 M NH4Cl
B. 1.0 M HNO2 and 1.0 M HNO3
D. All are
____16. Consider the reaction: C6F6(g) 3C2F2(g). Given that ΔH° = 591.1 kJ/mol and ΔG° = 495.4 kJ/mol at
25°C, calculate ΔS°.
A. 1.43 x 104kJ
B. -1.18 x 104kJ
C. 321 J/K
D. 3.65 kJ/K
____17. Consider a reaction for which ΔH° = 6.03 kJ/mol; ΔS° = 22.1 J/K-mol
Which of the following statements is true?
A. The reaction is spontaneous at all temperatures
B. The reaction becomes spontaneous at low temperatures below 273 K
C. The reaction becomes spontaneous at high temperatures above 273 K
D. The reaction is never spontaneous
____18. The pH of 0.10 M HCHO2 is 2.4 at 25°C. Calculate its acid dissociation constant at this temperature.
A. 4.0 x 10-3
B. 1.7 x 10-4
C. 4.0 x 10-4
D. 1.6 x 10-5
____19. Calculate the equilibrium constant at 25°C for the reaction: C6F6(g) 3C2F2(g). given that the
ΔG° = 495.4 kJ
A. 1.45 x 10-87
B. 1.58
C. 0.819
D. 1.22
____20. Given the following acid dissociation constants, pick the weakest conjugate base:
HC2H3O2 (Ka = 1.8 x 10-5); HF (Ka = 6.8 x 10-4); HClO (Ka = 3.0 x 10-8); HCN (Ka = 6.2 x 10-10);
A. C2H3O2-
B. F-
C. ClO-
D. CN-
Part II (8 points each)
Please show all your work for full credit.
1. a. What will be the pH upon addition 25 mL of 0.200 M KOH to 25 mL of 0.300 M HCl.
b. What will be the pH upon addition 45 mL of 0.200 M KOH to 25 mL of 0.300 M HCl.
2. Calculate the following:
a. The pH of a 500.0 mL solution containing 0.75 M HC3H5O3 (Ka = 1.4 x 10-4) and 0.25 M NaC3H5O3
b. The pH of the above solution after the addition of 0.10 mol NaOH. Assume no change in volume.
3. Consider the equilibrium: 2NO2(g) N2O4(g):
a. Calculate ΔGo for the reaction given that the ΔHo = -58.03 kJ/mol and the ΔSo = -176.6 J/K at 100C.
b. Calculate the equilibrium constant.
4. Consider a 0.10 M KClO solution; [Ka(HClO) = 3.0 × 10–8].
a. What is the Kb of ClO-?
b. Write the associated chemical EQUATION for hydrolysis by ClOc. Calculate the pH of a 0.10 M KClO solution.
5. A. Calculate the standard free energy change, ΔG° at 298 Kfor the reaction
2H2(g) + CO(g) → CH3OH(l).
The standard free energies of formation for CO & CH3OH(l) are -137 kJ and -166 kJ
B. Calculate the free energy change, ΔG, at 298 K, given that the partial pressures of CO & H2 are
5.0 atm & 3.0 respectively
C. Is the reaction spontaneous under these conditions.
Bonus Question
A 30.0 ml sample of 0.100 M HBrO. (Ka for HBrO = 2.3 × 10-9) is titrated with 0.100 M KOH.
a. Calculate the pH of the solution when 10.00 ml of KOH has been added
b. What will be the pH at the half-equivalence point?
c. What is the pH at the equivalence point?