The EMF of the Daniell cell is 1.1V . The external EMF to be applied for the following reaction to take place in it is:
$C u (s) + Z n {(a q)}^{2 +} \to C u {(a q)}^{2 +} + Z n (s)$

1.0 V

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1.1 V

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1.2 V

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0.55 V

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Solution

The correct option is C 1.2 V
The emf of the Daniell cell is $1.1 V$ . If an emf just smaller than that of the cell is applied, the reaction taking place in the cell is:

At anode: $Z n \to Z n^{2 +} + 2 e^{-}$

At cathode: $C u^{2 +} + 2 e^{-} \to C u$

Overall reaction $Z n + C u^{2 +} \to Z n^{2 +} + C u$

We need the reaction to take place in reverse direction then the external emf should be just greater than cell emf. Therefore, the answer is $1.2 V$ .

Option C is correct.

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(E^{\circ})

+ 1.1 V

Δ G^{\circ}

Z n (s) + C u_{(a q)}^{2 +} \to Z n_{(a q)}^{2 +} + C u (s)

(1 F = 96500 C / m o l)

Z n_{(s)} + {C u_{(a q)}}^{2 +} \to C u_{(s)} + {Z n_{(a q)}}^{2 +}

^{o}

^{2 +}

^{2 +}

1.1 V

Z n (s) + C u^{2 +} (a q .) \to Z n^{2 +} (a q .) + C u (s)

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Z n (s) | Z n^{2 +} (a q) | | C u^{2 +} (a q) | C u (s)

= 96487

Z n | Z n^{2 +} | | C u^{2 +} | C u

E_{c e l l} = 1.1 V

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