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CHEMISTRY 122
REVIEW PROBLEMS
1. a. Camphor has a melting point of 178.4 oC and a Kf of 37.7 oC/m. If 0.550 g of
an unknown nonelectrolyte lowered the freezing point of 35.0 g of camphor by
2.00 oC, what was the molar mass of the unknown?
b. When 1.00 g of hemoglobin is dissolved in enough water to form 100 mL of
solution, the osmotic pressure at 200C is 3.62 × 10-3 atm. What is the molar
mass of the protein, hemoglobin?
2. The equilibrium constant for the reaction I2(g) + Br2(g) ' 2 IBr(g) is 120.0. If
1.40 moles of I2 and 1.40 moles of Br2 react in a 3.50 L container, calculate
the equilibrium concentrations of I2, Br2 and IBr.
3. The rate law for the reaction, 2 NO2(g) + F2 (g) 2 NO2F(g), was
determined by following the rate of disappearance of F2(g). The rate law was
found to be Rate = k[NO2][F2]. Some scientists proposed the following
mechanism for this reaction:
NO2(g) + F2(g) NO2F(g) + F(g)
(slow)
F(g) + NO2(g) NO2F(g)
(fast)
Did the scientists propose a plausible mechanism or are they clearly
incorrect? Explain.
4. Determine the rate law and the rate constant (with proper units) for the
following reaction using the data given.
2 NO(g) + H2(g) N2O(g) + H2O(g)
[NO]
[H2]
Rate
6.4 × 10-3 M
2.2 × 10-3 M
2.5 × 10-5 M/s
12.8 × 10-3 M
2.2 × 10-3 M
1.0 × 10-4 M/s
6.4 × 10-3 M
4.4 × 10-3 M
5.0 × 10-5 M/s
5. Hypochlorous acid, HOCl, is a weak acid with Ka = 3.0 × 10-8. Calculate the
pH of a 0.0125 M solution of HOCl.
6. A buffer is prepared using HCN and NaCN. The resulting solution is 0.100 M
in HCN and 0.250 M in CN-1. The Ka of HCN is 6.2 × 10-10. Calculate the pH
of this buffer.
7. i. Calculate Ksp for CaF2 if the molar solubility of CaF2 is 2.0 x 10-4 M.
ii. a. For PbCl2, Ksp = 1.6 × 10-5. Calculate the molar solubility of PbCl2 in
pure water.
b. Calculate the molar solubility of PbCl2 in 0.10 M NaCl (NaCl is a strong
electrolyte).
8. Calcium carbonate, CaCO3, decomposes to produce calcium oxide (CaO,
quicklime) and CO2 at elevated temperatures.
CaCO3(s) _______> CaO(s) + CO2(g)
a) Calculate ΔHo (in kJ) for this reaction at 298 K. (Use tables in your text.)
b) Calculate ΔSo (in J/K) for this reaction at 298 K. (Use tables in your text.)
c) Calculate the minimum temperature at which the reaction will be productfavored.
(Assume no change in ΔH and ΔS with temperature.)
d) Determine what free energy change would accompany production of 7.75 g
of CaO via this process at 298 K.
9. A 0.10 M aqueous solution of the weak base, methylamine, CH3NH2, has a
pH of 11.30. Calculate the value of Kb for methylamine.
10. The decomposition of nitrogen pentoxide (N2O5) to nitrogen dioxide (NO2) and
oxygen (O2) proceeds via first-order kinetics. At 45 oC, the rate constant is
4.80 x 10-5 s-1. If 25.5 g of N2O5 were placed in a 5.00 L flask,
a) Calculate the concentration of N2O5 after 8 hours have elapsed.
b) Calculate the concentration of NO2 after 8 hours have elapsed if no NO2
was initially present in the flask.
c) How long would it take for the N2O5 concentration to drop to 0.0010 M?
d) What is the half-life for the decomposition of N2O5?
11. You need a buffer to maintain a pH of 3.20. How many grams of sodium
cyanate (NaOCN) would you need to add to 250 mL of a 0.125 M solution of
cyanic acid (HOCN, Ka = 3.5 × 10-4) to have the desired buffer? Assume no
volume change upon the addition of sodium cyanate.
12. A voltaic cell was constructed using the following half-reactions:
Cu2+(aq) + 2 e-1 Cu(s)
Sn2+(aq) + 2 e-1 Sn(s)
Determine the net cell reaction, the standard cell potential, E0cell, and ΔG°
for this cell. (Use the table of standard reduction potentials in your text.)
Does ΔGo indicate a product-favored or a reactant-favored reaction? Is this
consistent with a voltaic/galvanic cell? Explain your answer. Calculate the
cell potential at 25 oC if the concentration of Cu2+ is 0.100 M and the
concentration of Sn2+ is 0.010M.
13. Balance the following equation in acidic solution. Identify the oxidizing agent
and the reducing agent.
H2SO3(aq) + NO(aq) NO31-(aq) + S(s)
14. Determine the pH at the equivalence point for the titration of 200 mL of
0.0525 M NaCN with 0.0375 M HCl. The Ka for HCN is 4.9 x 10-10.