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General Chemistry Principles, Patterns, and Applications, 2011

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19.8 End-of-Chapter Material<br />

A P P L I C A T I ON PR OBLEMS<br />

Problems marked with a ♦ involve multiple concepts.<br />

1. The percent efficiency of a fuel cell is defined as ΔG°/ΔH° × 100. If hydrogen gas were distributed for<br />

domestic <strong>and</strong> industrial use from a central electrolysis facility, the gas could be piped to consumers much as<br />

methane is piped today. Conventional nuclear power stations have an efficiency of 25%–30%. Use tabulated<br />

data to calculate the efficiency of a fuel cell in which the reaction H 2 (g) + 1/2O 2 (g) → H 2 O(g) occurs under<br />

st<strong>and</strong>ard conditions.<br />

2. ♦ You are about to run an organic reaction <strong>and</strong> need a strong oxidant. Although you have BrO − 3 at your<br />

disposal, you prefer to use MnO − 4 . You notice you also have MnO 2 in the lab.<br />

a. Predict whether you will be able to synthesize MnO − 4 using the materials available to you.<br />

b. Write the overall reaction for the synthesis of MnO − 4 .<br />

c. What is ΔG° for this reaction?<br />

d. What is the equilibrium constant?<br />

3. It is possible to construct a galvanic cell using amalgams as electrodes, each containing different<br />

concentrations of the same metal. One example is the Pb(Hg)(a 1 )∣ PbSO 4 (soln)∣ Pb(Hg)(a 2 ) cell, in which<br />

a 1 <strong>and</strong> a 2 represent the concentrations of lead in the amalgams. No chemical change occurs; rather, the<br />

reaction transfers lead from one amalgam to the other, thus altering the Pb concentration in both amalgams.<br />

Write an equation for E for such a cell.<br />

4. ♦ The oldest known metallurgical artifacts are beads made from alloys of copper, produced in Egypt,<br />

Mesopotamia, <strong>and</strong> the Indus Valley around 3000 BC. To determine the copper content of alloys such as brass,<br />

a sample is dissolved in nitric acid to obtain Cu 2+ (aq), <strong>and</strong> then the pH is adjusted to 7.0. Excess KI is used to<br />

reduce the Cu 2+ to Cu + with concomitant oxidation of I − to I 2 . The iodine that is produced is then titrated with<br />

thiosulfate solution to determine the amount of Cu 2+ in the original solution. The following reactions are<br />

involved in the procedure:<br />

a. Cu 2+ (aq) + I − (aq) + e − → CuI(s); E° = 0.86 V<br />

b. S 4 O 2− 6 (aq) + 2e − → 2S 2 O 2− 3 (aq); E° = 0.08 V<br />

c. NO − 3 (aq) + 2H + (aq) + 2e − → NO − 2 (aq) + H 2 O(l); E° = 0.94 V<br />

Saylor URL: http://www.saylor.org/books<br />

Saylor.org<br />

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