Question

$ {{E}_{1}},{{E}_{2}},{{E}_{3}} $ are the emf values of the three galvanic cells respectively. (i) $ \text{Zn }\!\!|\!\!\text{ Zn}_{\text{1M}}^{\text{2+}}\text{ }\!\!|\!\!\text{ }\!\!|\!\!\text{ Cu}_{\text{0}\text{.1M}}^{\text{2+}}\text{ }\!\!|\!\!\text{ Cu} $ (ii) $ Zn|Zn_{1M}^{2+}||Cu_{1M}^{2+}|Cu $ (iii) $ Zn|Zn_{0.1M}^{2+}||Cu_{1M}^{2+}|Cu $ Which one of the following is true?

• A. $ {{E}_{2}}>{{E}_{3}}>{{E}_{1}} $
• B. $ {{E}_{3}}>{{E}_{2}}>{{E}_{1}} $
• C. $ {{E}_{1}}>{{E}_{2}}>{{E}_{3}} $
• D. $ {{E}_{1}}>{{E}_{3}}>{{E}_{2}} $

Answer 1

Answer: (B)

For the given cell, $ {{E}_{cell}}={{E}^{o}}cell-\frac{0.0591}{2}\log \frac{[Z{{n}^{2+}}]}{[C{{u}^{2+}}]} $ (i) $ {{E}_{1}}={{E}^{o}}cell-\frac{0.0591}{2}\log \frac{1}{0.1}={{E}^{o}}cell-\frac{0.0591}{2} $ (ii) $ {{E}_{2}}={{E}^{o}}cell-\frac{0.0591}{2}\log \frac{1}{1} $ $ ={{E}^{o}}cell-\frac{0.0591}{2}\times 0={{E}^{o}}cell $ (iii) $ {{E}_{3}}={{E}^{o}}cell-\frac{0.0591}{2}\log \frac{0.1}{1} $ $ ={{E}^{o}}cell+\frac{0.0591}{2} $ $ \therefore $ $ {{E}_{3}}>{{E}_{2}}>{{E}_{1}} $