Question

A solution containing one mole per litre of each Cu(NO3)2; AgNO3; Hg2(NO3)2; Mg(NO3)2 is being electrolysed using inert electrodes. The values of standard electrode potentials (reduction potentials in volts are Ag/Ag+ = 0.80 V, 2Hg/ Hg2++ = 0.79 V, Cu/Cu++ = + 0.34 V , Mg/Mg++ - 2.37 V. With increasing volt age, the sequence of deposition of metals on the cathode will be

• A. Ag, Hg, Cu
• B. Cu, Hg, Ag
• C. Ag, Hg, Cu, Mg
• D. Mg, Cu, Hg, Ag

Answer 1

Answer: (A)

Ag, Hg, Cu

Answer 2

Greater the value of standard reduction potential, greater will be it’s tendency to undergo reduction . So the sequence of deposition of metals on cathdoe will be Ag, Hg, Cu. Here magnesium will not be deposited because its’ standard reduction potential is negative . So it is strong tandency to undergo oxidation. Therefore, on electrolysis of Mg(NO3)2 solution, H2 gas will be evolved at cathode.