Question

If $E _{ Ni ^{2+} \mid Ni }^{\circ}=0.25 V , E _{ Cu ^{2+} \mid Cu }^{\circ}=0.34 V , E _{ Ag ^{+} \mid Ag }^{\circ}=0.8 V$ and $E_{Z n^{2+} \mid Z n}^{0}=-0.76 V ,$ then which of the following reactions under standard condition will not take place in the specified direction spontaneously ?

• A. $Cu _{( s )}+ Ni _{( aq. )}^{2+} \rightarrow Cu _{( aq .)}^{2+}+ Ni _{(s)}$
• B. $Cu _{( s )}+2 Ag _{( aq. )}^{+} \rightarrow Cu _{( aq .)}^{2+}+2 Ag _{( s )}$
• C. $Cu _{( s )}+ Zn _{( aq .)}^{+2} \rightarrow Cu _{( aq .)}^{2+}+ Zn _{( s )}$
• D. Both (a) & (c)

Answer 1

Answer: (D)

Since, $Cu ^{+2} / Cu$ has higher standard reduction potential than $Ni ^{+2} / Ni \& Zn ^{+2} / Zn$

$\therefore Cu ^{+2}$ gets reduced faster than $Ni ^{+2} \& Zn ^{+2}$