Redox Reactions And Electrochemistry Ques 125
Question: A solution containing one mole per litre of each $ Cu{{(NO_3)}_2},AgNO_3,Hg_2{{(NO_3)}_2} $ and $ Mg{{(NO_3)}_2}, $ is being electrolysed by using inert electrodes. The values of standard electrode potentials in volts (reduction potentials) are $ Ag/A{g^{+}}=+0.80,2Hg/Hg_2^{2+}=+0.79,Cu/C{u^{2+}}=+0.34, $ $ Mg/M{g^{2+}}=-2.37 $ with increasing voltage, the sequence of deposition of metals on the cathode will be [IIT 1984; AMU 1999; Kerala PMT 2004]
Options:
A) $ Ag,Hg,Cu,Mg $
B) $ Mg,Cu,Hg,Ag $
C) $ Ag,Hg,Cu $
D) $ Cu,Hg,Ag $
Show Answer
Answer:
Correct Answer: C
Solution:
A cation having highest reduction potential will be reduced first and so on. However, $ M{g^{2+}} $ in aqueous solution will not be reduced $ ( E_{M{g^{2+}}/Mg}^{0}<E_{H_2O/\frac{1}{2}H_2+O{H^{-}}}^{{}} ) $ . Instead water would be reduced in preference.
