Chemistry 65.100 A, V
Midterm Test #3
January 29, 1999

Part A. Answer each question with a few sentences or equations where necessary. (5 Marks each)

1. Write balanced oxidation, reduction and overall reactions for an electrochemical cell having the shorthand notation:

Al_(s) | Al⁺³_(aq) || H⁺_(aq), H_2(g) | Pt_(s)

2. Referring to the attached reduction potentials table, state whether or not iodine, I_2(s), can oxidize nickel metal to Ni⁺²_(aq), and explain your answer.

3. Why is it impossible to electrowin aluminum metal from an aqueous solution of Al⁺³_(aq)?

4. Name two reasons why dry cells eventually die.

5. Briefly explain how a sacrificial anode protects a metal object from corrosion.

6. Diethyl ether, shown below, is a polar molecule with a tetrahedral shape around the O atom, similar to water. Would diethyl ether hydrogen bond with itself? Why or why not?

1. Electrochemical reduction can be used to determine the amount of gold in a sample. The sample is dissolved, and the Au⁺³_(aq) is reduced to Au_(s) at a cathode. What mass of gold will be deposited in 1.00 hour by a current of 1.50 Amperes?

2. For the lead acid battery, answer the following questions:

(a) Write the oxidation, reduction and overall reactions.
(b) Write the expression for the reaction quotient, Q.
(c) The cell potential can be predicted by measuring the pH of the electrolyte. If the pH = -1.00, calculate the cell potential at 25^oC. Recall that pH = -log₁₀[H⁺_(aq)], and note that [H⁺_(aq)] = [HSO₄^-_(aq)]. E^o for this cell = 1.924 V.

3. List ALL of the intermolecular forces that would exist between each of the following pairs of molecules or atoms:

(a) Ar and Ar
(b) HF_(g) and H₂O_(g)
(c) Br^-_(aq) and H₂O_(l)
(d) H₂ and H₂O

4. Use the Clausius Clapeyron equation to calculate the vapor pressure of water at 85^oC. The normal boiling point of water is 100^oC, and its heat of vaporization is 40.7 kJ mol^-1.