The standard reduction potentials of ${Zn}^{2 +}\ |\ Zn\ ,\ {Cu}^{2 +}\ |\ Cu\ and\ {Ag}^{+}\ |\ Ag$ are respectively – 0.76, 0.34 and 0.8 V. The following cells were constructed I $Zn\ |\ {Zn}^{2 +}\ ||\ \ {Cu}^{2 +}\ |\ Cu$ II $Zn\ |\ {Zn}^{2 +}\ ||\ \ {Ag}^{+}\ |\ Ag$ III $Cu\ |\ {Cu}^{2 +}\ ||\ {Ag}^{+}\ |\ Ag$ What is the correct order of $E_{cell}^{{^\circ}}$ of these cells?

Question

Dr. Abubacker · Accepted Answer

(b)
Given,
${Zn}^{2 +}\ \  \rightarrow \ Zn\ ,\ \ \ \ \ \ \ E^{{^\circ}}\ \  = \  - \ 0.76\ V$
${Cu}^{2 +}\ \  \rightarrow \ Cu\ ,\ \ \ \ \ \ \ E^{{^\circ}}\  = \ \ 0.34\ V$
${Ag}^{+}\ \  \rightarrow \ Ag\ ,\ \ \ \ \ \ \ \ E^{{^\circ}}\  = \ \ 0.8\ V$
Cell reaction of (I) is
$Zn\  + \ {Cu}^{2 +}\  \rightarrow \ {Zn}^{2 +}\  + \ Cu$
$E_{cell}^{{^\circ}} = \ E_{oxidation}\  + \ E_{reduction}\$
= + 0.76 + 0.34
= + 1.10 V
Cell reaction of (II) is
$Zn\  + \ {Ag}^{+}\  \rightarrow \ {Zn}^{2 +}\  + \ Ag$
$E_{cell}^{{^\circ}}\  = \ 0.76\  + \ 0.8$
= + 1.56 V
Cell reaction of (III) is
$Cu\  + \ {Ag}^{+}\  \rightarrow \ {Cu}^{2 +}\  + \ Ag$
$E_{cell}^{{^\circ}}\  = \  - 0.34\  + \ 0.8$
= + 0.46
So, the correct order of $E_{cell}^{{^\circ}}$ of these cell is
II > I > III.

Explanation

Reviewed by Dr. Abubacker

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