CHEM 220 – Final Exam Review
1.
Consider the decomposition of chromium (III) iodide.
A) What is the K for the reaction?
B) Diagram a standard, electrolytic cell for the electrolysis of an aqueous solution of chromium (III) iodide.
C) What voltage must be applied in order for the cell to work?
2.
The decomposition of phosphine, PH3: 4 PH3(g) → P4(g) + 6 H2(g) is found to be second order. In an experiment at 500.0ºC,
the initial concentration of 1.0 M PH3 fell to 0.50 M PH3 in 121 s.
A) How long does it take for a 0.250 M solution of phosphine to decrease to 0.085 M?
B) What is the rate of the reaction when [PH3] = 0.155 M
3.
Consider the reaction below for which KC=5.5 x 106. An initial mixture contains 1.00 mol of methane, 2.00 mol of water, 5.00
mol carbon monoxide, and 4.00 mol hydrogen gas in a 2.0 L container. What will be the equilibrium concentrations of reactants
and products at equilibrium?
3 H2(g) + CO(g)  CH4(g) + H2O(g)
4.
Given the initial rate data for the reaction A + B → C,
[A], M
0.10
0.10
0.20
[B], M
0.20
0.40
0.40
Δ[C]/Δt (initial) M/s
4.20 × 10-4
1.68 × 10-3
3.38 × 10-3
Determine the differential rate expression for the reaction.
5. pH titration:
A 20.0-mL sample of an unknown monoprotic acid (HA) of unknown concentration was titrated using standardized
0.117 M NaOH solution. The pH was monitored during the titration, and the following titration plot was prepared:
A) Indicate the equivalence point on the graph. What is the pH at equivalence? Why is it above 7.0?
B) What is the concentration of the unknown acid?
C) What is the Ka of the unknown acid?
D) The technician titrating the sample forgot to record the pH of the acid before the titration was started. Calculate
the pH of the weak acid solution before any NaOH was added. (Do not just extrapolate from the graph.)