Q. A solution containing one mole per litre of each $Cu\left( {NO}_{3} \right)_{2},\ {\ AgNO}_{3},\ {Hg}_{2}\left( {NO}_{3} \right)_{2}\$and$\ Mg\left( {NO}_{3} \right)_{2}$ is being electrolysed by using inert electrodes. The values of standard electrode potentials in volts (reducing potentials) are ${Ag/Ag}^{+} = + 0.80,\ 2{Hg/Hg}^{2 +} = + 0.79,\ {Cu/Cu}^{2 +} = + 0.34,\ {Mg/Mg}^{2 +} = - 2$ With increasing voltage, 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) $Mg,\ Cu,\ Hg,\ Ag$
Explanation
(a)
A cation having highest reduction potential will be reduced first and so on. However, ${Mg}^{2 +}$ in aqueous solution will not be reduced $\left( E_{{Mg}^{2 +}/\ Mg}^{{^\circ}} < E_{H_{2}O/\frac{1}{2}\ H_{2} + {OH}^{-}\ } \right).$ Instead water would be reduced in preference
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.