Electrochemistry - Result Question 8
####9. The equivalent conductance of $\frac{M}{32}$ solution of a weak monobasic acid is $8.0 mho cm^{2}$ and at infinite dilution is $400 mho cm^{2}$. The dissociation constant of this acid is:
(a) $1.25 \times 10^{-6}$
(b) $6.25 \times 10^{-4}$
(c) $1.25 \times 10^{-4}$
(d) $1.25 \times 10^{-5}$
[2009]
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Solution:
- (d) Degree of dissociation,
$ \begin{aligned} & \alpha=\frac{\Lambda}{\Lambda _{\infty}}=\frac{8.0}{400}=2 \times 10^{-2} \\ & K_a=\frac{C \alpha^{2}}{(1-\alpha)} \approx C \alpha^{2}=\frac{1}{32} \times(2 \times 10^{-2})^{2} \end{aligned} $
$ =1.25 \times 10^{-5} $
