Question

For purification of copper, a thin plate of pure copper and a thick rod of impure copper are used as electrodes. Copper from the impure rod is sought to be transferred to the thin copper plate. Which electrode should be attached to the positive terminal of the battery?

(A) Pure copper
(B) Copper
(C) Impure copper
(D) Aluminum

Answer 1

The impure copper rod should be attached to the positive terminal as the anode. The pure copper plate should be connected to the negative terminal as the cathode. Through this electrolytic process, copper is transferred from the anode to the cathode, purifying it.

Step-by-step explanation:

For the purification of copper using electrolytic cells, the thick rod of impure copper should be attached to the positive terminal of the battery, making it the anode. At the anode, copper metal (Cu) is oxidized to copper ions (Cu²⁺). These copper ions then dissolve into the solution. The thin plate of pure copper should be connected to the negative terminal, becoming the cathode, where the reduction of copper ions back to pure copper metal (Cu) occurs. As the process continues, copper is transferred from the impure anode to the pure cathode, purifying the copper in the process.

The cathode will see a growth in mass as the copper metal is deposited on its surface, and the concentration of copper ions near the cathode will decrease as they are reduced and plated onto the cathode. The process used here is similar to that of electroplating, where a thin layer of metal is coated onto another material for decorative, protective, or conductive purposes. Commonly used metals for electroplating include gold, silver, nickel, chromium, and indeed, copper.