PHYSICAL CHEMISTRY IN BRIEF

CHAP. 11: ELECTROCHEMISTRY [CONTENTS] 356

Solution

a) We calculate the mass of discharged aluminium from relation (11.8)

mAl=

27 × 0. 1 × 3600

3 × 96485. 3

= 0. 034 g.

b) The mass of aluminium sulfate that was used up during the electrolysis will be calculated from

relation (11.9)

m=

343 × 0. 1 × 3600

3 × 2 × 96485. 3

= 0, 213 g.

c) Oxidation of the anion SO^24 −and the reaction of the radical SO· 4 with water occur at the

anode. Overall we may write

SO^24 −+H 2 O=H 2 SO 4 +

1

2

O 2 + 2 e−.

If we use relation (11.10), whereνO 2 = 1/2 andze= 2, we have

mO 2 =

32 × 0. 1 × 3600

2 × 96485. 3

×

1

2

= 0. 030 g.

11.2.3 Coulometers.

Coulometers are devices measuring the electric charge that has passed through an electric
circuit. In these apparatuses electrolysis proceeds while either the gain in the electrode mass
(coulometer for silver or copper) or the volume of gas discharged during the electrolysis (electrolytic-
gas coulometer) is measured. The charge passed through the circuit is measured using Faraday’s
law.