Question

$E_{1}, E_{2}$ and $E_{3}$ are the emf values of the three galvanic cells respectively.
(i) $Z n\left|Z n_{1 M}^{2+}\right|\left|C u_{0.1 M}^{2+}\right| C u$
(ii) $Zn \left|Z n_{1 M}^{2+}\right|\left|C u_{1 M}^{2+}\right| C u$
(iii) $Z n\left|Z n_{0.1 M}^{2+} \| C u_{1 M}^{2+}\right| C u$
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,
$
E _{\text {cell }}= E _{\text {cell }}^{ o }-\frac{0.0591}{2} \log \frac{\left[ Zn ^{2+}\right]}{\left[ Cu ^{2+}\right]}
$
(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) $E _{3}= E _{\text {cell }}^{ o }-\frac{0.0591}{2} \log \frac{0.1}{1}= E _{\text {cell }}^{ o }+\frac{0.0591}{2}$
$
\therefore E _{3}> E _{2}> E _{1}
$