ANS:D - Pure copper electrodes are used as anode for electro-refinning of copper.

In the electrorefining of copper, pure copper electrodes are indeed used as anodes. Here's how the process works:

1. Setup: The setup consists of a tank containing an electrolyte solution of copper sulfate (CuSO4​) with sulfuric acid (H2​SO4​) added to increase conductivity. Inside the tank, there are two electrodes: the anode and the cathode. The anode is made of impure copper, while the cathode is made of pure copper.
2. Electrolysis: When an electric current is passed through the electrolyte solution, copper ions (Cu2+) from the anode are oxidized and dissolved into the electrolyte, increasing the concentration of copper ions in the solution. This process is known as oxidation.

Anode (oxidation):Cu→Cu2++2e−

3. Copper Deposition: Simultaneously, at the cathode, copper ions in the solution are reduced and deposited onto the cathode as solid copper metal. This process is known as reduction.

Cathode (reduction):Cu2++2e−→Cu

4. Purity Enhancement: As the copper ions from the anode dissolve into the electrolyte, impurities such as silver, gold, and other metals remain behind as sludge or settle at the bottom of the tank. The deposited copper at the cathode gradually builds up as a pure copper sheet or plate.
5. Collection: The pure copper deposited on the cathode is periodically removed from the tank, washed, and further processed to obtain high-grade copper metal.

By using pure copper electrodes as anodes, the electrorefining process ensures that the impurities present in the starting material (such as blister copper) are left behind at the anode, while the pure copper is selectively deposited onto the cathode. This process allows for the production of high-purity copper suitable for various industrial applications, such as electrical wiring, electronics, and plumbing.