JEE Advanced levelSingle correct optionDifficulty 3 of 3ec133
100mL of 0.10MCuSOX4 is electrolysed between platinum electrodes with a steady current of 0.50A. Take F=96500Cmol−1 and neglect volume changes. Which statement is correct?
AAfter 3860s the cathode product changes from Cu to HX2 and the solution is then 0.10M in HX2SOX4
BAfter 1930s the cathode product changes from Cu to HX2 and the solution is then 0.05M in HX2SOX4
CAfter 3860s oxygen starts to evolve at the cathode
DCopper deposition continues indefinitely because CuX2+ is regenerated at the anode
Answer: A
Moles of CuX2+=0.100×0.10=0.0100mol, needing 0.0200mol of electrons, i.e. Q=0.0200×96500=1930C, so t=1930/0.50=3860s. Up to this time the anode reaction 2HX2OOX2+4HX++4eX− produces 0.0200molHX+, i.e. 0.0100molHX2SOX4 in 100mL, which is 0.10M. Once CuX2+ is exhausted, HX+ (or water) is reduced at the cathode and HX2 evolves. Platinum anode cannot supply CuX2+, so (D) is false.