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.

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.

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.

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

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)

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

Electroplating Eating utensils are electroplated with silver.

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

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−