Question

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:

$Cu\left(s\right)+Zn{\left(aq\right)}^{2+}\to Cu{\left(aq\right)}^{2+}+Zn\left(s\right)$

• A. 1.1 V
• B. 0.55 V
• C. 1.2 V
• D. 1.0 V

Answer 1

Answer: (C)

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

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

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

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

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 $1.2V$.

Option C is correct.