Question

Three iron pieces $A,B,C$ are taken. $B$ is coated with zinc and the coating is worn away partially. $C$ is coated with tin and the coating is worn away partially. Explain the rate at which $A,B,C$ undergo rusting on exposure to air. Give reason.

Answer 1

When zinc coating is worn away partially also, zinc can protect iron from rusting. Zinc has higher oxidation potential than iron. Zinc undergoes oxidation in preference to iron. Thus,zinc is called sacrificial anode. But, in case to tin, when the coating is worn away partially, tin cannot prevent iron from rusting. Instead, it renders faster rusting than normal uncoated iron sheet. This is because tin has a lower oxidation potential than iron. When both the metals are exposed to atmosphere, iron only undergoes oxidation and tin acts as cathode. By providing cathode, it helps faster oxidation of iron.