Question

Electricity is passed through an acidic solution of Cu$^{2+}$ till all the Cu$^{2+}$ was exhausted, leading to the deposition of 300 mg of Cu metal. However, a current of 600 mA was continued to pass through the same solution for another 28 minutes by keeping the total volume of the solution fixed at 200 mL. The total volume of oxygen evolved at STP during the entire process is ___ mL. (Nearest integer)
Given:
$\mathrm{Cu^{2+} + 2e^- \rightarrow Cu(s)}$ 
$\mathrm{O_2 + 4H^+ + 4e^- \rightarrow 2H_2O}$ 
Faraday constant = 96500 C mol$^{-1}$ 
Molar volume at STP = 22.4 L 
 

Hint:

In electrolysis problems, calculate charge separately for metal deposition and gas evolution.

Answer 1

Correct Answer: 112

Step 1: Calculate moles of copper deposited.
\[ n_{\mathrm{Cu}} = \frac{0.300}{63.54} \approx 0.0047 \text{ mol} \]
Step 2: Calculate charge used for copper deposition.
\[ Q = 2 \times 0.0047 \times 96500 \approx 907 \text{ C} \]
Step 3: Calculate charge passed in 28 minutes.
\[ Q = 0.6 \times 28 \times 60 = 1008 \text{ C} \]
Step 4: Calculate moles of oxygen evolved.
\[ n_{\mathrm{O_2}} = \frac{1008}{4 \times 96500} \approx 0.0026 \]
Step 5: Calculate volume of oxygen at STP.
\[ V = 0.0026 \times 22.4 = 0.058 \text{ L} = 112 \text{ mL} \]
Step 6: Final conclusion.
Total volume of oxygen evolved is 112 mL.