Question

The equivalent conductance of solution M÷32of a weak
monobasic acid is 8.0 mhos cm2 and at infinite dilution
400 mhos cm2. The dissociation constant of this acids:
(AIPMT-2009)
(1) 1.25 x 10-4
(2) 1.25 x 10-5
(3) 1.25 x 10-6
(4) 6.25 x 10-4​

Answer 1

Answer:

The degree of dissociation is related to equivalent conductance and equivalent conductance at infinite dilution :

The degree of dissociation α = Λ(equivalent conductance at given dilution)/Λ∞(equivalent conductance at given dilution)

= 8 mho cm2/400 mho cm2

Dissociation constant of an acid Ka = C α2

= 1/32 M x (8 mho cm2/400 mho cm2)2

= 1.25 x 10-5

Correct answer is 2.