Question

In the purification of metals, it is recommended to use the impure metal as the anode and the pure metal as the cathode. Why not in the other way?

Answer 1

Because of the electron flow in the cell, the metals move from the anode to the cathode. For example in the purification of a mix of gold-silver dore the impure metal is cast into anodes. The electrolyte is something that will dissolve the silver, usually involving nitric acid. The silver goes into solution and is driven onto the cathode. The gold not being soluble falls to the bottom as sludge that is recovered and later melted into gold bars. If the process is reversed you would just plate pure metal over the impure metal.