An aqueous solution containing one mole per litre of each Cu(NO3)2, AgNO3, Hg2(NO3)2 and Mg(NO3)2, is being electrolysed by using inert electrodes. The values of standard electrode potentials in volts (reduction potentials) are Ag/Ag+=+0.80, 2Hg/Hg2+2=+0.79, Cu/Cu2+=+0.34, Mg/Mg2+=−2.37 with increasing voltage, the sequence of deposition of metals on the cathode will be
A cation that has the highest reduction potential will be reduced first and so on.
However, Mg2+ in aqueous solution will not be reduced (E∘Mg2+/Mg<EH2O/12H2+OH−). Instead water would be reduced in preference.