Question

A salt $M{A}_2$, ionises as: $M{A}_2\rightleftharpoons M^{2+}+2A^{-}$. It was found that a given solution of the salt had the same freezing point as a solution of glucose of twice the molarity. The apparent degree of ionisation of the salt is:

• A. 0.25
• B. 0.33
• C. 0.5
• D. 0.67

Answer 1

Answer: (C)

0.5

Initially, $\Delta T_f=K_b\times m$ ----------------(1)

Now in solution, m' = m x 2

$\Rightarrow \Delta T_f=i{K}_b\times m$ -----------------(2)

(2) / (1) , $\Rightarrow 2i=1\Rightarrow i=1/2=0.5$