The equivalent conductance of `M//32` solution of a weak monobasic acid is `8.0 ` and at infinite dilution is `400 `. The dissociation constant of this acid is :

Options

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

Answer

D

Explanation

Given , `Lambda = 8 ` mho `cm^(2)`
`Lambda_(0) = 400 mho cm^(2)`
Degree of dissociation ,
`alpha = (Lambda)/(Lambda_(0)) implies alpha = (8)/(400) = 2 xx 10^(-2)`
Dissociation constant , `K = C alpha^(2)`
Given , C = M/32
`therefore K = (1)/(32) xx 2 xx 10^(-2) xx 2 xx 10^(-2)`
`K = 1.25 xx 10^(-5)`