Question

During electro refining of Cu by electrolysis of an aqueous solution of CuSO₄ using copper electrodes, if 2.5 g of Cu is deposited at cathode, then at anode

• A. decrease of more than 2.5 g of mass takes place
• B. 450 ml of O₂ at STP is liberated
• C. 2.5 g of copper is deposited
• D. a decrease of 2.5 g of mass takes place

Answer 1

Answer: (A)

decrease of more than 2.5 g of mass takes place

Answer 2

At the cathode: $Cu^{2+}(aq) + 2e^- \rightarrow Cu(s)$. If 2.5 g of Cu is deposited, 2.5 g of $Cu^{2+}$ ions were reduced. At the anode: $Cu(s) \rightarrow Cu^{2+}(aq) + 2e^-$. To deposit 2.5 g of Cu at the cathode, 2.5 g of Cu must dissolve from the anode. However, the anode is impure. More reactive metals (impurities) are also oxidized and dissolve, increasing the total mass loss at the anode beyond 2.5 g.