During electrolysis of aqueous solution of a salt pH in the space near one of the electrodes is increased. Which of the following salt solution was electrolysed?

Options

A. KCl
B. `CuCl_(2)`
C. `Cu(NO_(3))_(2)`
D. `CuSO_(4)`

Answer

To determine which salt solution was electrolyzed during the electrolysis of an aqueous solution that resulted in an increase in pH, we can analyze the behavior of the ions present in the given salt solutions. The options provided are KCl, CuCl2, Cu(NO3)2, and CuSO4.

### Step-by-Step Solution:

1. **Identify the Ions in Each Salt**:
- KCl dissociates into K⁺ and Cl⁻.
- CuCl2 dissociates into Cu²⁺ and 2Cl⁻.
- Cu(NO3)2 dissociates into Cu²⁺ and 2NO3⁻.
- CuSO4 dissociates into Cu²⁺ and SO4²⁻.

2. **Consider the Electrolysis Process**:
- During electrolysis, cations are reduced at the cathode and anions are oxidized at the anode.
- The reduction potential of the ions will determine which species gets reduced or oxidized.

3. **Reduction Potentials**:
- For K⁺: E° = -2.93 V
- For Cu²⁺: E° = +0.34 V
- For Cl⁻: E° = +1.36 V (for oxidation to Cl2)
- H2O can also be reduced to produce OH⁻ and H2.

4. **Analyzing KCl**:
- At the cathode, water can be reduced to produce OH⁻:
\[ \text{H2O} + e^- \rightarrow \frac{1}{2} \text{H2} + \text{OH}^- \]
- At the anode, Cl⁻ can be oxidized to Cl2:
\[ 2\text{Cl}^- \rightarrow \text{Cl2} + 2e^- \]
- The increase in OH⁻ concentration will increase the pH, making the solution basic.

5. **Analyzing CuCl2, Cu(NO3)2, and CuSO4**:
- In these cases, the reduction at the cathode will primarily involve Cu²⁺ being reduced to Cu:
\[ \text{Cu}^{2+} + 2e^- \rightarrow \text{Cu} \]
- At the anode, water will be oxidized, producing H⁺ ions:
\[ \text{H2O} \rightarrow \frac{1}{2} \text{O2} + 2\text{H}^+ + 2e^- \]
- The increase in H⁺ concentration will decrease the pH, making the solution acidic.

6. **Conclusion**:
- The only salt solution that results in an increase in pH (making the solution basic) is KCl, as it produces OH⁻ ions during the electrolysis process.

### Final Answer:
The salt solution that was electrolyzed is **KCl**.