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).