Electrolytic cells: Getting chemical reactions from electricity

An electrolytic cell uses electricity to produce a desired redox reaction. For instance, water can be decomposed by the use of electricity in an electrolytic cell. The overall cell reaction is

2 H₂O(l) → 2 H₂(g) + O₂(g)

In a similar fashion, you can produce sodium metal and chlorine gas by the electrolysis of molten sodium chloride. Producing chemical changes by passing an electric current through an electrolytic cell is called electrolysis. This reaction may be the recharging of a battery (as you see the next section) or one of many other applications. For instance, ever wonder how the aluminum in that aluminum can is mined?

Aluminum ore is primarily aluminum oxide (Al₂O₃). People produce aluminum metal by reducing the aluminum oxide in a high-temperature electrolytic cell using approximately 250,000 amps. That’s a lot of electricity. Taking old aluminum cans, melting them down, and reforming them into new cans is far cheaper than extracting the metal from the ore. That’s why the aluminum industry is strongly behind the recycling of aluminum. It’s just good business.

Electrolytic cells are also used in a process called electroplating. In electroplating, a more-expensive metal is plated (deposited in a thin layer) onto the surface of a cheaper metal by electrolysis. Back before plastic auto bumpers became popular, chromium metal was electroplated onto steel bumpers. Those five-dollar gold chains you can buy are really made of some cheap metal with an electroplated surface of gold.