Question

A 0.075 molar solution of monobasic acid has a freezing point of –0.18°C. Calculate Ka for the acid, (kf = 1.86)

Answer 1

We know,
Molarity formula:

ΔTf = Kf x m
=> 1.86 x 0.075
=> 0.1395°C
So,
i = 0.18/0.1395 [ Vant Hoff Factor]
=> 1.29

We know,


α = i - 1/n-1  

α = 1.29-1/2-1
   = 0.29

Constant disassociation: 

Ka = α²C
      =  (0.29)² x 0.075
      = 6.31 x 10^-3