Question

Impure metal should be made the anode and pure metal should be made the cathode. Why would the anode corrode and become thinner?

Answer 1

Due to oxidation and reduction half-equations.

Explanation:

Whether we discuss the galvanic cell or the electrolytic cell, the phenomenon is the same.

You should know that always oxidation reaction occurs on the anode and the reduction reaction occurs at the cathode.

Let us discuss the example of a galvanic cell where Aluminum (`Al`) represents the anode and lead (`Pb`) represents the cathode. The half-equations are:

Anode: `Al(s)->Al^(3+)(aq)+3e^(-)` (Oxidation).

Cathode: `Pb^(2+)(aq)+2e^(-)->Pb(s)` (Reduction).

From the half-equations we can notice that we are consuming `Al(s)` and therefore, the anode weigh will decrease , and we are producing `Pb(s)` and thus the weigh of the cathode will increase.

Here is a video that explains the particulate representation of what occurs during the operation of a galvanic cell: