Final Exam, Spring 2004

1. Complete and balance the following reactions:

a. H₂SO₄(aq) + NaOH(aq)

b. Pb(NO₃)₂(aq) + NaCl(aq)

c. Zn²⁺(aq) + NH₃(aq)

d. C₆H₅NH₂(aq) + H₂O(l)

e. Cr³⁺(aq) + H₂O(l)

f. NiCl₂(aq) + K₃PO₄(aq)

g. HF(aq) + CH₃NH₂(aq)

h. Fe(NO₃)₂(aq) + KCl(aq)

i. VO₂⁺(aq) + S(s) → VO²⁺(aq) + H₂SO₃(aq)

j. [Cr(OH)₄]^–(aq) + ClO₃^–(aq) → CrO₄^2–(aq) + Cl^–(aq)

2. Consider the following reaction:

HgCl₂(aq) + C₂O₄^2–(aq) → Cl^–(aq) + CO₂(g) + Hg₂Cl₂(s)

a. Balance the reaction.

b. The following rate data was collected:

[HgCl₂] (M) [C₂O₄^2–] (M) Initial rate (mol L^–1 min^–1)

 

0.105 0.15 1.8×10^–5

 

0.105 0.30 7.1×10^–5

 

0.052 0.30 3.5×10^–5

 

0.052 0.15 8.9×10^–6

 

Determine the order of reaction with respect to HgCl₂, with respect to C₂O₄^2–, and the overall order.

c. Write the rate law for the reaction.

3. Al(OH)₃ is a sparingly soluble salt. Determine if the solubility will increase, decrease, or stay the same in the following solutions. Briefly (15 words or less) explain your answer.

a. 1 M HCl solution.

b. 1 M NaClO₄ solution.

c. 1 M NH₃ solution.

d. 1 M NaOH solution.

4. You need to prepare a buffer with pH = 6.00 and a buffer capacity of about 0.1 M.

a. Which substances should you use to prepare the buffer?

b. 0.010 mol of NaOH is added to 1.0 L of your buffer; estimate the new pH.

c. 1.00 mol of NaOH is added to 1.0 L of your buffer; estimate the new pH.

5. An assumption that we make about the group 2 hydroxides is that both hydroxides completely dissociate. This question will test that assumption using magnesium hydroxide as an example.

a. Write the hydrolysis reaction for the magnesium ion.

b. Find ΔG° for the reaction in part a.

c. Find the equilibrium constant at 25 °C for the reaction in part a.

d. What subscript should be used with the equilibrium constant found in part c?

e. Estimate the pH and per cent ionization of a 1 M solution of magnesium ion.

f. The per cent dissociation of the second hydroxide in magnesium hydroxide is equal to 100 – (per cent ionization of magnesium ion). Based on the result in part e, is it justifiable to assume that both hydroxides should be considered strong? Why or why not?

6. This question will use available data to fill in a value in the Table of Thermodynamic Quantities.

a. Write the hydrolysis reaction for Co²⁺(aq).

b. Find ΔG° at 25 °C for the reaction in part a.

c. Find ΔG_f° for the cobalt(II) monohydroxide cation.

d. A common mistake beginning students make is to write the hydrolysis reaction for Co²⁺(aq) to give cobalt(II) hydroxide. Find ΔG° for this hypothetical reaction and explain why the reaction does not occur.

7. Consider the cell:

Co(s) | Co²⁺(aq) pH = 0 || AgCl(s) | Cl^–(aq) | pH = 0 | Ag(s)

a. Write the oxidation half–reaction.

b. Write the reduction half–reaction.

c. Write the net reaction.

d. Find the cell potential under standard conditions.

e. Is the reaction spontaneous or nonspontaneous? Why?

f. Write the mass action expression for the net reaction that would be used in the Nernst equation.

g. Will the spontaneity increase or decrease if the concentration of chloride ion is increased in the cell? Why?

Answers