The Foundations of Chemistry

The number of coulombs passing through the cell is 7.50 103 C. For every 4(9.65 104
coulombs) passing through the cell, 22.4 L of O 2 at STP is produced.

_?_LSTPO 2 7.50^103 C

9.6

1

5

m



ol

1

e

0



 (^4) C
22
4
.4
m
L
o
S
l
TP
e
O 2
 0.435 LSTPO 2
You should now work Exercise 28.
Notice how little product is formed by what seems to be a lot of electricity. This suggests
why electrolytic production of gases and metals is so costly.
COMMERCIAL APPLICATIONS OF
ELECTROLYTIC CELLS
Several elements are produced commercially by electrolysis. In Sections 21-3 to 21-5, we
described some electrolytic cells that produce sodium (the Downs cell), chlorine, hydrogen,
and oxygen. Electrolysis of molten compounds is also the common method of obtaining
other Group IA metals, IIA metals (except barium), and aluminum (Section 22-3). Impure
metals can also be refined electrolytically, as we will describe for copper in Section 22-8.
Metal-plated articles are common in our society. Jewelry and tableware are often plated
with silver. Gold is plated onto jewelry and electrical contacts. Copper is plated onto many
objects for decorative purposes (Figure 21-5). Some automobiles have steel bumpers plated
21-7
21-7 Commercial Applications of Electrolytic Cells 857
See the Saunders Interactive
General Chemistry CD-ROM,
Screen 21.11, Coulometry.
A family memento that has been
electroplated with copper. To aid in
electroplating onto nonconductors,
such as shoes, the material is first
soaked in a concentrated electrolyte
solution to make it conductive.

Cu anode

Cathode

Object to be plated

CuSO 4

solution

Cu2+

e–

Copper

atom, Cu

Copper

ion, Cu2+ e–

Copper

atom, Cu

Copper

ion, Cu2+

Figure 21-5 Electroplating with

copper. The anode is made of pure

copper, which dissolves during

the electroplating process. This

replenishes the Cu^2 ions that are

removed from the solution as Cu

plates out on the cathode.