Houston Community College System
Chemistry 1412
Exam # 2
Summer 2011
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 acid of HSO4-?
A. H2SO4–
B. H2SO4
C. SO4-2
D. H3O+
____2. Which of these species will have the lowest entropy (S°) at 25°C?
A. CH3OH(l)
B. CH3OH(g)
C. C2H5OH(l)
D. C2H5OH(g)
____3. A sample of orange juice has a hydroxide concentration of 3.5 x 10-11 M. What is the pH?
A. 3.11
B. 3.31
C. 3.54
D. 10.46
____4. An aqueous solution of Cu(NO3)2 will have a pH that is
A. Acidic
B. Basic
C. Neutral
D. cannot be determined
____5. What is the pH of a buffer solution consisting of 0.400 M HCN (Ka = 6.2x10-10) and 0.600 M
sodium cyanide, NaCN
A. 9.21
B. 9.61
C.9.03
D. 9.38
____6. Which of the following do you predict to be the strongest acid?
A. HClO2
B. HBrO2
C. HBrO
D. HClO
____7. If X is the molar solubility of a salt, which of the following solubility product
expressions is incorrect?
A. Ag2CO3, Ksp=4X3
B. AgClO3, Ksp=X2
C. CaS, Ksp=X2
D. FePO4, Ksp=16X2
C. 0.40
D. Cannot be determined
____8. What is pH of 0.10M HClO4(aq)
A. 0.10
B. 1.0
____9. The molar solubility of silver sulfate, Ag2SO4, in pure water is 0.0144 M. Calculate
the value of Ksp for silver sulfate from this data.
A. 2.99 x 10-6
B. 1.19 x 10-5
C. 2.39 x 10-6
D. 5.97 x 10-6
____10. Determine the pH of a Ba(OH)2 solution made by dissolving 0.200 mol Ba(OH)2 in 500 mL
of solution.
A. 13.6
B. 13.9
C. 13.3
D. 13.0
_____11. Which response includes all of the following processes that are accompanied by an decrease in
entropy?
1) I2(s) → I2(g)
2) 2I(g) → I2(g)
3) 2NH3(g) → N2(g) + 3H2(g)
4) Mg2+(aq) + 2OH–(aq) → Mg(OH)2(s)
A. 1,2
B. 1, 3
C. 3,4
D. 2,4
____12. Calculate the entropy change (J/mole.K) of the reaction. The molar entropies [So] are given in
brackets after each substance.
Bi2O3(s) [151.5] + 3 CO(g) [197.7]
A. 35.2
B. 9.9
2 Bi(s) [56.7] + 3 CO2(g) [213.7]
C. 79.5
D. -79.5
____13. Which of the following has Gf°=0 & Hf°=0?
A. I2(g)
B. O3(g)
C. H2O(l)
D. Br2(l)
____14. Which one of the following is a buffer solution?
A. 1.0 M HCl and 1.0 KCl
C. 1.0 M NH3 and 1.0 M NH4Cl
B. 1.0 M HNO3 and 1.0 M HNO2
D. 1.0 M HNO3 and 1.0 M NaOH
____15. Sodium carbonate can be made by heating sodium bicarbonate:
2NaHCO3(s) → Na2CO3(s) + CO2(g) + H2O(g)
Given that ΔH° = 128.9 kJ/mol and ΔG° = 33.1 kJ/mol at 25°C, calculate ΔS°.
A. 3.83 kJ/K-mol
B. -3.83 kJ/K-mol
C. 0.321 kJ/K-mol
-9.73 x 103kJ/K-mol
____16. Consider a reaction for which ΔH° = –199.0 kJ/mol; ΔS° = –41.00J/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 4854 K
C. The reaction becomes spontaneous at high temperatures above 48.54 K
D. The reaction is never spontaneous
____17. What is the pH of 0.100 M HCHO2 (Ka for HCHO2 = 1.77 × 10-4)
A. 1.00
B. 3.75
C. 2.38
D. 4.75
____18. At 1500°C the equilibrium constant for the reaction CO(g) + 2H2(g) CH3OH(g) has the value
Kp = 1.4 × 10–7. Calculate ΔG° for this reaction at 1500°C.
A. 105 kJ/mol
B. 233 kJ/mol
C. -105 kJ/mol
D. 1.07 kJ/mol
____19. The pH of a 0.020 M solution of an unknown weak acid, HA, is 5.0. The % ionization of the acid is
A. 10-3
B. 2.5
C. 0.050
D. 0.40
____20. Which of the following is not a hydrolysis reaction?
A. NH3(aq) + H2O(l)  H3O+(aq)+OH-(aq)
B. Sn+4(aq) +H2O(l)SnOH+3(aq) + H+(aq)
C. NH3(aq) + HCl(aq)  NH4Cl(aq)
D. All are hydrolysis reactions
Part II (8 points each)
Please show all your work for full credit.
1. a. What will be the pH upon addition 30 mL of 0.200 M NaOH to 25 mL of 0.300 M HNO3.
b. What will be the pH upon addition 40 mL of 0.200 M NaOH to 25 mL of 0.300 M HNO3.
2. The solubility product constant Ksp of Mn(OH)2 is 2.1x1013 at 25°C. The molar mass of Mn(OH)2 is 88.96
g/mol.
a. Calculate its molar solubility
b. Calculate its solubility in g/L
3. The equilibrium constant for the reaction PbI2 (s) Pb+2(aq) + 2I– (aq) is Ksp = 8.5 × 10–9 at 25°C.
a. Calculate ΔGo for the reaction.
b. Calculate ΔG for the reaction when [Pb+2] = 2.0 × 10–3 M and [I–] = 1.0 × 10–3 M.
c. Is the reaction spontaneous or nonspontaneous at these concentrations?
4. Consider a 0.10 M KF solution; [Ka(HF) = 6.8 × 10–4].
a. What is the Kb of F-?
b. Write the associated chemical EQUATION for hydrolysis by Fc. Calculate the pH of a 0.10 M KF solution.
5. Calculate the standard free energy change, ΔG° and the equilibrium constant, K, at 298 K for the
reaction SO2(g) + NO2(g) → SO3(g) + NO(g).
ΔG°f
SO2(g)
–300.4 kJ/mol
SO3(g)
–370.4 kJ/mol
NO(g)
86.7 kJ/mol
NO2(g)
51.8 kJ/mol
Bonus Question
A 25.0 ml sample of 0.200 M HClO. (Ka for HClO = 3.0 × 10-8) is titrated with 0.200 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?