The equivalent conductance of `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 :

Options

A. `1.25 xx 10^(-5)`
B. `1.25 xx 10^(-6)`
C. `6.25 xx 10^(-4)`
D. `1.25 xx 10^(-4)`

Answer

A

Explanation

`alpha= (Lamda)/(Lamda_(D))= (8.0)/(400)= 2 xx 10^(-2)`
`K_(a)= (C alpha^(2))/((1- alpha)) ~~ C alpha^(2)= (1)/(32) xx (2 xx 10^(-2))^(2)= 1.25 xx 10^(-5)`