1. Chapter 15 Oxidation and Reduction
15.5 Oxidation−Reduction Reactions that Require Electrical Energy
Learning Goal Describe the half-cell reactions and the overall reactions that occur in electrolysis.

2. Nonspontaneous Oxidation−Reduction Reactions
In the activity series, the oxidation of copper is below zinc. This means the reaction is not spontaneous:
Cu(s) + Zn2+(aq)  Cu2+(aq) + Zn(s)
Not spontaneous
To make this reaction take place, we need an electrolytic cell that uses an electrical current to drive the nonspontaneous reaction.

3. Nonspontaneous Oxidation−Reduction Reactions
Figure 15.5 In this electrolytic cell, the Cu anode is in a Cu2+ solution, and the Zn cathode is in a Zn2+ solution. Electrons provided by a battery reduce Zn2+ to Zn and drive the oxidation of Cu to Cu2+ at the Cu anode.

4. Electrolysis of Sodium Chloride
When molten NaCl is electrolyzed,
the products are sodium metal and chlorine gas
electrodes are placed in a mixture of Na+ and Cl− and connected to a battery
the products are separated to prevent them from reacting with each other

5. Electrolysis of Sodium Chloride
When molten NaCl is electrolyzed,
electrodes leave the anode as Cl− is oxidized to Cl2
2Cl−(l)  Cl2 (g) + 2 e−
electrons flow to the cathode, Na+ is reduced to sodium metal, Na
2Na+(l) + 2 e−  2Na(l)
the overall reaction is
2Cl−(l) + 2Na+(l)  Cl2 (g) + 2Na(l)

6. Electroplating
Electroplating uses electrolysis to coat an object with a thin layer of metal such as silver, platinum, or gold, for example
car bumpers and hubcaps are electroplated with chromium
bowls, silverware, and platters are electroplated with silver

7. Electroplating
Eating utensils are electroplated with silver.

8. Learning Check
What half-reaction takes place when Au3+ solution is used to gold plate a stainless steel earring?

9. Solution
What half-reaction takes place when Au3+ solution is used to gold plate a stainless steel earring? The half-reaction is reduction, Au3+(aq)  Au(s) + 3 e−