1.1 What is Chemistry?

23.3. Electrolysis http://www.ck12.org

FIGURE 23.11

An electrolytic cell uses an external power

source (a battery) to drive a nonspon-

taneous reaction. The copper half-cell

undergoes oxidation, while the zinc half-

cell undergoes reduction.

Oxidation (anode): Cu(s)→Cu^2 +(aq)+2e− E^0 =− 0 .34 V

Reduction (cathode): Zn^2 +(aq)+2e−→Zn(s) E^0 =− 0 .76 V

Overall reaction: Cu(s)+Zn^2 +(aq)→Cu^2 +(aq)+Zn(s) E^0 cell=− 1 .10 V

The standard cell potential is negative, indicating a nonspontaneous reaction. The battery must be capable of
delivering at least 1.10 V of direct current in order for the reaction to occur.

Commercial Electrolysis Reactions

Electrolysis of Molten Sodium Chloride

Several electrolysis reactions are commonly performed on a large scale for the commercial production of certain
substances. For example, molten (liquid) sodium chloride can be electrolyzed to produce sodium metal and chlorine
gas. The electrolytic cell used in this process is called a Down’s cell (Figure23.12).

In a Down’s cell, the liquid sodium ions are reduced at the cathode to liquid sodium metal. At the anode, liquid
chloride ions are oxidized to chlorine gas. The reactions and cell potentials are shown below.

Oxidation (anode): 2Cl−(l)→Cl 2 (g)+2e− E^0 =− 1 .36 V

Reduction (cathode): Na+(l)+e−→Na(l) E^0 =− 2 .71 V

Overall reaction: 2Na+(l)+2Cl−(l)→2Na(l)+Cl 2 (g) E^0 cell=− 4 .07 V

The battery must supply over 4 volts to carry out this electrolysis. This reaction is a major industrial source of