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7. Electrochemistry eLearn.Punjab
Brine ionizes to produce ions:

Reaction at anode (oxidation):

Reaction at cathode (reduction):

2H+(aq) + 2e_ → H2(g)

Overall cell reaction of this process:

i. Anode of Downs cell is made of a non-metal, what is its name? What is the function
of this anode?

ii. Where is the sodium metal collected in Downs cell?
iii. What is the name of the by-product produced in the Downs cell?
iv. Are anodes of Downs cell and Nelson cell made of same element? If yes, what is its

name ?
v. What is the shape of cathode in Nelson’s cell? Why is it perforated?
vi. Which ions are discharged at cathode in Nelson’s cell and what is produced at

cathode?

7.7 CORROSION AND ITS PREVENTION

Corrosion is slow and continuous eating away of a metal by the surrounding medium. It is a redox
chemical reaction that takes place by the action of air and moisture with the metals. The most
common example of corrosion is rusting of iron.

7.7.1 Rusting of Iron

Corrosion is a general term but corrosion of iron is called rusting. The important condition for
rusting is moist air (air having water vapours in it). There will be no rusting in water vapours free of
air or air free of water. Now we study the chemistry of the rusting process. Stains and dents on the
surface of the iron provide the sites for this process to occur. This region is called anodic region and

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