Name: _______________

1. An acidified solution of KMnO₄ is often used as a reactant in an oxidation-reduction titration because KMnO₄

I. is a strong oxidizing agent.

II. is a strong reducing agent.

III. has a color change which is a natural indicator for the end-point.

A. I only B. II only

C. II and III only D. I and III only

2. Which change correctly represents a reduction process?

A. ClO^- à ClO₃^- B. Al à Al³⁺

C. N₂O à N₂O₄ D. BiO₃^- à Bi³⁺

3. Lead metal, silver metal, a Pb(NO₃)₂ aqueous solution, and a AgNO₃ aqueous solution are the reagents used in an electrochemical cell. Which solution concentrations give the greatest voltage?

Reduction Potentials

Pb²⁺ + 2 e^- à Pb E° = - 0.13 V

Ag⁺ + e^- à Ag E° = 0.80 V

Pb(NO₃)₂ AgNO₃

A. 0.01 M 1.0 M

B. 1.0 M 0.10 M

C. 1.0 M 1.0 M

D. 0.10 M 0.10 M

4. Molten AlCl₃ is electrolyzed for 5.0 hr using a current of 0.40 A. Metallic aluminum is produced at one electrode and chlorine gas, Cl₂, is produced at the other. How many grams of aluminum will be produced?

A. 0.40 g B. 0.67 g

C. 1.0 g D. 2.0 g

5. Which proposed reaction will be spontaneous and have the greatest potential under standard conditions?

Reduction Potentials

Al³⁺ + 3 e^- à Al E° = - 1.68 V

Cr³⁺ + 3 e^- à Cr E° = - 0.744 V

Cr³⁺ + e^- à Cr²⁺ E° = - 0.408 V

Cd²⁺ + 2 e^- à Cd E° = - 0.402 V

A. Al + Cr³⁺ à Al³⁺ + Cr

B. 2 Al³⁺ + 3 Cd à 2 Al + 3 Cd²⁺

C. Al + 3 Cr²⁺ à Al³⁺ + 3 Cr³⁺

D. 2 Cr²⁺ + Cd²⁺ à 2 Cr³⁺ + Cd

6. An aqueous solution of KI is electrolyzed. Which reaction occurs at the cathode?

A. K⁺ (aq) + e^- à K (s)

B. 2 I^- (aq) à I₂ (g) + 2 e^-

C. 2 H₂O (l) à 4 H⁺ (aq) + O₂ (g) + 4 e^-

D. 2 H₂O (l) + 2 e^- à H₂ (g) + 2 OH^- _(aq)

7. In which of these is the oxidation number of sulfur +4?

A. H₂SO₄

B. H₂S

C. S₂O₃^2-

D. SO₃^2-

8. What is the coefficient for OH^- when this equation is balanced in aqueous solution using the smallest whole number coefficients?

OH^- + MnO₄^- + SO₃^2- à SO₄^2- + MnO₄^2- + H₂O

A. 1 B. 2 C. 3 D. 4

9. Which species is the reducing agent in this reaction?

Cr₂O₇^2- + 6 I^- + 14 H⁺ à 3 I₂ + 2 Cr³⁺ + 7 H₂O

A. Cr₂O₇^2- B. Cr³⁺ C. I^- D. I₂

10. Which statement is true for the cell as it discharges?

Zn / Zn²⁺ (1.0 M) ║ Sn²⁺ (1.0 M) / Sn

A. The concentration of Zn²⁺ increases

B. Oxidation occurs at the tin electrode

C. The mass of the tin electrode decreases

D. Electrons flow from the tin electrode to the zinc electrode

Free Response

1993 Free Response #7

A galvanic cell is constructed using a chromium electrode in a 1.00-molar solution of Cr(NO₃)₃ and a copper electrode in a 1.00-molar solution of Cu(NO₃)₂. Both solutions are at 25° C.

(a) Write a balanced net ionic equation for the spontaneous reaction that occurs as the cell operates. Identify the oxidizing agent and the reducing agent.

(b) A partial diagram of the cell is shown below.

(i) Which metal is the cathode?

(ii) What additional component is necessary to make the cell operate?

(iii) What function does the component in (ii) serve?

(c) How does the potential of this cell change if the concentration of Cr(NO₃)₃ is changed to 3.00-molar at 25° C? Explain.

2. Answer the following questions that refer to the galvanic cell shown in the diagram above.

(a) Identify the anode of the cell and write half-reaction that occurs there.

(b) Write the net ionic equation for the overall reaction that occurs as the cell operates and calculate the value of the standard cell potential. E°_cell

(c) Indicate how the value of E_cell would be affected if the concentration of Ni(NO₃)₂ (aq) was changed from 1.0 M to 0.10 M and the concentration of Zn(NO₃)₂ (aq) remained at 1.0 M. Justify your answer.

(d) Specify whether the value of K_eq for the cell reaction is less than 1, greater than 1, or equal to 1. Justify your answer.