Question

$E_1,E_2$ and $E_3$ are the emf values of the three galvanic cells respectively.
(i) $Zn\left|Z{n}_{1M}^{2+}\right|\left|C{u}_{0.1M}^{2+}\right|Cu$
(ii) $Zn\left|Z{n}_{1M}^{2+}\right|\left|C{u}_{1M}^{2+}\right|Cu$
(iii) $Zn\left|Z{n}_{0.1M}^{2+}\Vert C{u}_{1M}^{2+}\right|Cu$
Which one of the following is true ?

• A. $E_2>E_1>E_5$
• B. $E_1>E_2>E_3$
• C. $E_3>E_1>E_2$
• D. $E_3>E_2>E_1$

Answer 1

Answer: (D)

For the given cell,
$<br/>E_{\text{cell }}=E_{\text{cell }}^o-\frac{0.0591}{2}\log \frac{\left[Z{n}^{2+}\right]}{\left[C{u}^{2+}\right]}<br/>$
(i) $E_1=E_{\text{cell }}^o-\frac{0.0591}{2}\log \frac{1}{0.1}=E_{\text{cell }}^o-\frac{0.0591}{2}$
(ii) $E_2=E_{\text{cell }}^o-\frac{0.0591}{2}\log \frac{1}{1}=E_{\text{cell }}^o-\frac{0.0591}{2}\times 0=E_{\text{cell }}^o$
(iii) $E_3=E_{\text{cell }}^o-\frac{0.0591}{2}\log \frac{0.1}{1}=E_{\text{cell }}^o+\frac{0.0591}{2}$
$<br/>\therefore E_3>E_2>E_1<br/>$