Q24 / 180 · COMEDK 2023 (Memory Based) · Chemistry

Assuming no change in volume, the time required to obtain solution of $\mathrm{pH}=4$ by electrolysis of $100 \mathrm{~mL}$ of $0.1 \mathrm{M} \mathrm{NaOH}$ (using current $0.5 \mathrm{~A}$ ) will be

  • Correct answer
    A
    1.93s
  • B
    2.63s
  • C
    1.80s
  • D
    4.26s

Solution

$\left[\mathrm{H}^{+}\right]=10^{-4} \mathrm{M}$ No. of moles of $\mathrm{NaOH}$ in $100 \mathrm{~mL}$ solution $=\frac{M V}{1000}=\frac{10^{-4} \times 100}{1000}=10^{-5}$ Mass of $\mathrm{NaOH}$ in solution $=10^{-5} \times 40=4 \times 10^{-4} \mathrm{~g}$ By Faraday's law, $W=\frac{I t E}{96500}$ $\begin{aligned} \text{or} \quad 4 \times 10^{-4} & =\frac{0.5 \times t \times 40}{96500} \\ t & =\frac{4 \times 10^{-4} \times 96500}{0.5 \times 40}=1.93 \mathrm{~s}\end{aligned}$

Hence, the correct answer is option: 'A'.

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