Question

The standard potentials of $Ag^+/Ag, Hg_2^{2+}/2Hg, Cu^{2+}/Cu$ and $Mg^{2+}/Mg$ electrodes are $0.80,0.79, 0.34$ and $-2.37\, V$, respectively. An aqueous solution which contains one mole per litre of the salts of each of the four metals is electrolyzed. With increasing voltage, the correct sequence of deposition of the metals at the cathode is

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

Answer 1

Answer: (D)

$Mg,Cu,Hg,Ag$

Answer 2

More the reduction potential, more is the deposition of metals at cathode. Cation having $E^0$ value less than $- 0.83\,V$ (reduction potential of $H_2O$) will not deposit from aqueous solution. Hence correct order of A deposition of the metal at the cathode is $Ag > Hg >Cu$