Q70 / 197 · NEET 2009 (Mains) · Chemistry

The equivalent conductance of $\frac{M}{32}$ solution of a weak monobasic acid is 8.0 mho $\mathrm{cm}^2$ and at infinite dilution is 400 mho $\mathrm{cm}^2$, The dissociation constant of this acid is -

  • A
    $1.25 \times 10^{-4}$
  • Correct answer
    B
    $1.25 \times 10^{-5}$
  • C
    $1.25 \times 10^{-6}$
  • D
    $6.25 \times 10^{-4}$

Solution

$$ \begin{aligned} \alpha= & \frac{\mathrm{A}_{\mathrm{C}}}{\mathrm{A}_{\infty}}=\frac{8}{400} \\ \mathrm{~K}_{\mathrm{a}} & =\mathrm{C}^2 \\ & =\frac{1}{32} \times \frac{8}{400} \times \frac{8}{400} \\ & =1.25 \times 10^{-5} \end{aligned} $$

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

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