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General Chemistry Principles, Patterns, and Applications, 2011

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c. FeCl 3<br />

2. Electrolysis is the most direct way of recovering a metal from its ores. However, the Na + (aq)/Na(s),<br />

Mg 2+ (aq)/Mg(s), <strong>and</strong> Al 3+ (aq)/Al(s) couples all have st<strong>and</strong>ard electrode potentials (E°) more negative than the<br />

reduction potential of water at pH 7.0 (−0.42 V), indicating that these metals can never be obtained by<br />

electrolysis of aqueous solutions of their salts. Why? What reaction would occur instead?<br />

3. What volume of chlorine gas at st<strong>and</strong>ard temperature <strong>and</strong> pressure is evolved when a solution of MgCl 2 is<br />

electrolyzed using a current of 12.4 A for 1.0 h?<br />

4. What mass of copper metal is deposited if a 5.12 A current is passed through a Cu(NO 3 ) 2 solution for 1.5 h.<br />

5. What mass of PbO 2 is reduced when a current of 5.0 A is withdrawn over a period of 2.0 h from a lead<br />

storage battery?<br />

6. Electrolysis of Cr 3+ (aq) produces Cr 2+ (aq). If you had 500 mL of a 0.15 M solution of Cr 3+ (aq), how long would<br />

it take to reduce the Cr 3+ to Cr 2+ using a 0.158 A current?<br />

7. Predict the products obtained at each electrode when aqueous solutions of the following are electrolyzed.<br />

a. AgNO 3<br />

b. RbI<br />

8. Predict the products obtained at each electrode when aqueous solutions of the following are electrolyzed.<br />

a. MgBr 2<br />

b. Hg(CH 3 CO 2 ) 2<br />

c. Al 2 (SO 4 ) 3<br />

A N S W E R S<br />

1.<br />

2.<br />

3. 5.2 L<br />

4.<br />

5.<br />

6.<br />

7.<br />

a. cathode: Ag(s); anode: O 2 (g);<br />

b. cathode: H 2 (g); anode: I 2 (s)<br />

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

Saylor.org<br />

1807

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