Daniel cell, the EMF of the cell can b e increased b y

Options

A. increasing the concentration af `Zn^(+)` ions
B. decreasing the concentration of `Cu^(2+)`
C. increasing the concentration of `Cu^(2+)`
D. decreasing the concentration of `Zn^(2+)` ions

Answer

To determine how to increase the EMF (electromotive force) of a Daniel cell, we need to analyze the cell reaction and the Nernst equation.

### Step-by-Step Solution:

1. **Understand the Cell Reaction**:
The Daniel cell consists of a zinc electrode and a copper electrode. The overall cell reaction can be written as:
\[ \text{Cu}^{2+} + \text{Zn} \rightarrow \text{Cu} + \text{Zn}^{2+} \]

2. **Write the Nernst Equation**:
The EMF of the cell can be expressed using the Nernst equation:
\[ E_{\text{cell}} = E^\circ - \frac{0.0591}{n} \log \left( \frac{[\text{Zn}^{2+}]}{[\text{Cu}^{2+}]} \right) \]
where \(E^\circ\) is the standard EMF of the cell, \(n\) is the number of moles of electrons transferred (which is 2 for this reaction), and \([\text{Zn}^{2+}]\) and \([\text{Cu}^{2+}]\) are the concentrations of zinc and copper ions, respectively.

3. **Identify Factors Affecting EMF**:
To increase the EMF of the cell, we need to minimize the term:
\[ \log \left( \frac{[\text{Zn}^{2+}]}{[\text{Cu}^{2+}]} \right) \]
This can be achieved by either:
- Decreasing the concentration of \([\text{Zn}^{2+}]\)
- Increasing the concentration of \([\text{Cu}^{2+}]\)

4. **Evaluate the Options**:
- **Option 1**: Increasing the concentration of \([\text{Zn}^{2+}]\) - This would increase the log term, decreasing the EMF.
- **Option 2**: Decreasing the concentration of \([\text{Cu}^{2+}]\) - This would increase the log term, decreasing the EMF.
- **Option 3**: Increasing the concentration of \([\text{Cu}^{2+}]\) - This would decrease the log term, increasing the EMF.
- **Option 4**: Decreasing the concentration of \([\text{Zn}^{2+}]\) - This would decrease the log term, increasing the EMF.

5. **Conclusion**:
The EMF of the Daniel cell can be increased by:
- Increasing the concentration of \([\text{Cu}^{2+}]\) (Option 3)
- Decreasing the concentration of \([\text{Zn}^{2+}]\) (Option 4)

### Final Answer:
The EMF of the Daniel cell can be increased by:
- **Increasing the concentration of copper ions (\([\text{Cu}^{2+}]\))**.
- **Decreasing the concentration of zinc ions (\([\text{Zn}^{2+}]\))**.