FARADAY’S LAW OF ELECTROLYSIS
In 1832–1833, Michael Faraday’s studies of electrolysis led to this conclusion.
The amount of substance that undergoes oxidation or reduction at each electrode
during electrolysis is directly proportional to the amount of electricity that passes
through the cell.This is Faraday’s Law of Electrolysis.A quantitative unit of electricity is now called the
faraday.
One faradayis the amount of electricity that corresponds to the gain or loss, and
therefore the passage, of 6.022 1023 electrons, or one moleof electrons.A smaller electrical unit commonly used in chemistry, physics, and electronics is the
coulomb (C).One coulomb is defined as the amount of charge that passes a given point
when 1 ampere (A) of electric current flows for 1 second. One ampere of current equals
1 coulomb per second. One faraday is equal to 96,485 coulombs of charge.
1 ampere (^1)
c
s
o
e
u
c
l
o
o
n
m
d
b
or 1 A1 C/s
1 faraday6.022 1023 e96,485 C
Table 21-1 shows the amounts of several elements produced during electrolysis by the
passage of 1 faraday of electricity.
21-6
TABLE 21-1 Amounts of Elements Produced at One Electrode in Electrolysis by 1 Faraday of Electricity
Number of e Product
Half-Reaction in Half-Reaction (electrode) Amount Produced
Ag(aq)e88nAg(s) 1 Ag (cathode) 1 mol107.868 g
2H(aq) 2 e88nH 2 (g) 2 H 2 (cathode) ^12 mol1.008 g
Cu^2 (aq) 2 e88nCu(s) 2 Cu (cathode) ^12 mol31.773 g
Au^3 (aq) 3 e88nAu(s) 3 Au (cathode) ^13 mol65.656 g
2Cl88nCl 2 (g) 2 e 2 Cl 2 (anode) 2 ^1 mol35.453 g11.2 LSTP
2H 2 O() 88nO 2 (g)4H(aq) 4 e 4 O 2 (anode) ^14 mol8.000 g5.60 LSTP
Michael Faraday (1791–1867) is considered the greatest experimental scientist of the
nineteenth century. As a bookbinder’s apprentice, he educated himself by extensive reading.
Intrigued by his self-study of chemistry and by a lecture given by Sir Humphry Davy, the
leading chemist of the day, Faraday applied for a position with Davy at the Royal Institution.
He subsequently became director of that laboratory. His public lectures on science were very
popular.
For comparison, a 100-watt household
light bulb uses a current of about 0.8
ampere.