CHEM 1215 Unit 5 Electrochemistry Practice Problems

You will need to use Appendix E from your text for some of these problems.

1. Determine the oxidation number for each element in the following compounds:

a. P₂O₅

b. NH₄ClO₄

c. NaHCO₃

d. Sn(SO₄)₂

e. H₂C₂O₄

f. LiAlH₄

2. Determine whether each reaction shown below is a redox reaction. For each redox reaction, identify the element oxidized, element reduced, oxidizing agent, and reducing agent.

a. H₂C₂O₄ (aq) + 2 NaOH (aq) à Na₂C₂O₄ (aq) + 2 H₂O (l)

b. CuSO₄ (aq) + Mg (s) à MgSO₄ (aq) + Cu (s)

c. 2 SO₂ (g) + O₂ (g) à 2 SO₃ (g)

d. Fe₂O₃ (s) + 3 CO (g) à 2 Fe (s) + 3 CO₂ (g)

e. PbS (s) + 4 H₂O₂ (aq) à PbSO₄ (s) + 4 H₂O (l)

3. Balance the following redox reactions.

a. MnO₄^- (aq) + Cl^- (aq) à Mn²⁺ (aq) + Cl₂ (g) (acidic solution)

b. MnO₄^- (aq) + I^- (aq) à MnO₂ (s) + I₂ (aq) (basic solution)

4. A galvanic cell is composed of two half cells, one containing aluminum and aluminum ion and the other containing nickel and nickel (II) ion. Use this information to answer the following questions.

a. Sketch the galvanic cell, labeling all parts.

b. Identify the metal at the anode.

c. Identify the metal at the cathode.

d. Write the reaction that occurs at the anode.

e. Write the reaction that occurs at the cathode.

f. Write the overall reaction for the galvanic cell.

g. Calculate the standard cell potential for the galvanic cell.

5. A galvanic cell is composed of two half cells, one containing zinc and zinc ion and the other containing copper (I) and copper (II) ions. Use this information to answer the following questions.

a. Sketch the galvanic cell, labeling all parts.

b. Identify the anode.

c. Identify the cathode.

d. Write the reaction that occurs at the anode.

e. Write the reaction that occurs at the cathode.

f. Write the overall reaction for the galvanic cell.

g. Calculate the standard cell potential for the galvanic cell.

6. Identify the strongest oxidizing agent in each pair.

a. O₂ vs. O₃

b. ClO₃^- vs. BrO₃^-

7. The redox reaction between sulfur and arsenic acid takes place in acidic solution. Using the skeleton for this reaction (shown below), answer the following questions.

S (s) + H₃AsO₄ (aq) à H₂SO₃ (aq) + H₃AsO₃ (aq)

a. Balance the reaction

b. Identify the element oxidized and the element reduced.

c. Identify the oxidizing agent.

d. Calculate the standard emf for the reaction, E^o_rxn .

e. Calculate the value for the equilibrium constant for this reaction at 25^oC.

f. Calculate the emf for the reaction, E_rxn, at 25^oC when [H₃AsO₄] = 0.100 M, [H₂SO₃] = 2.50 M, and [H₃AsO₃] = 3.00 M.

8. What will happen to the emf for the reaction shown in question 3a when each of the following changes is made?

a. Solid sodium hydroxide is added?

b. The partial pressure of chlorine increases?

c. Solid sodium chloride is added?

d. Solid potassium permanganate is added?

9. Calculate E^o_rxn for each of the following reactions. Identify each as spontaneous or nonspontaneous under standard conditions.

a. MnO₂ + 2 Cl^- + 4 H⁺ à Mn²⁺ + Cl₂ + 2 H₂O

b. NO₃^- + Bi + 2H⁺ à NO + BiO⁺ + H₂O

10. Given the following half reaction and standard reduction potential, calculate the equilibrium constant for the oxidation of iron (II) ion by S₂O₆^2- at 25^oC.

S₂O₆^2- (aq) + 4 H⁺ (aq) + 2 e^- à 2 H₂SO₃ (aq) E^o_red = +0.60V

11. What volume of 0.125 M hydrochloric acid is needed to neutralize 1.55 g of magnesium hydroxide?

12. What volume of 1.25 M sodium hydroxide is needed to neutralize 25.0 mL of 3.00 M sulfuric acid?

13. What is the molarity of a solution prepared by dissolving 10.0 g of aluminum nitrate in enough water to prepare 250.0 mL of solution?

14. A reaction is first order with respect to A and third order with respect to B. By what factor will the rate change when the [B] is doubled while [A] remains constant?

15. Write a balanced equation for the complete neutralization of H₃C₆H₅O₇ by calcium hydroxide.