Question

At 27 °C, the pH of 1 L of aqueous copper sulfate is 5.5. This solution was electrolyzed using two Pt electrodes for some time. What is the pH of remaining copper sulfate solution?

• A. \(5.5\)
• B. More than 5.5 but less than 7.0
• C. \(7.5\)
• D. Less than 5.5 but more than zero

Hint:

In electrolysis, consider both reduction and oxidation reactions at the cathode and anode, respectively, to determine the overall effect on solution pH.

Answer 1

The Correct Option is D

Step 1: Understanding electrolysis of CuSO\(_4\).
Aqueous CuSO\(_4\) ionizes as follows: \[ {CuSO}_4 \rightleftharpoons {Cu}^{2+} + {SO}_4^{2-} \] During electrolysis using Pt electrodes:
At the cathode, Cu\(^{2+}\) is reduced:
\[ {Cu}^{2+} + 2e^- \rightarrow {Cu (s)} \] At the anode, oxidation of water occurs instead of sulfate ion: \[ 2H_2O \rightarrow O_2 + 4H^+ + 4e^- \] Step 2: Effect on pH.
The removal of Cu\(^{2+}\) ions from the solution does not significantly affect the pH.
However, oxidation of water at the anode increases H\(^{+}\) concentration, lowering the pH.
Since the initial pH was 5.5, the increase in H\(^{+}\) ions causes the solution to become more acidic.
Step 3: Conclusion. The pH of the solution decreases, but it remains greater than 0.
Thus, the correct answer is (4) Less than 5.5 but more than zero.
Therefore, the pH decreases but remains above zero, aligning with option (4).

Answer 2

To solve this problem, we need to analyze the effect of electrolysis on the pH of a copper sulfate solution.

1. Understanding Electrolysis and pH Change:
When a copper sulfate (CuSO₄) solution is electrolyzed using platinum (Pt) electrodes, the electrolysis process leads to the decomposition of the copper sulfate. Copper is deposited at the cathode, and oxygen is released at the anode. This process affects the pH of the solution.

2. Reaction at the Electrodes:
- At the cathode, copper ions (Cu²⁺) are reduced to form solid copper (Cu). - At the anode, water is oxidized to form oxygen gas (O₂) and hydrogen ions (H⁺), which increase the acidity of the solution.

3. Effect on pH:
Since hydrogen ions (H⁺) are produced at the anode, the pH of the solution will decrease, making the solution more acidic. This results in the pH being less than 5.5, but not approaching zero, since some copper sulfate remains and the solution is not highly acidic.

4. Conclusion:
After electrolysis, the pH of the remaining copper sulfate solution will be less than 5.5 but more than zero.

Final Answer:
The correct answer is Option D: Less than 5.5 but more than zero.