Question

A dilute solution contains ‘x’ moles of solute A in 1 kg of solvent with molar elevation constant $K_b$. The solute dimerises in the solution according to the following equation. The degree of association is $\left(\alpha \right)$:

$2A\rightleftharpoons A_2$

The Van’t Hoff factor will be:

• A. $i=1-2\alpha$
• B. $i=1-\frac{\alpha }{2}$
• C. $i=1+\frac{\alpha }{2}$
• D. $i=1+a$

Answer 1

The correct option is B $i=1-\frac{\alpha }{2}$

$2A\rightleftharpoons A_2;n=2$

$i=1+(\frac{1}{n}-1)\alpha =1-\frac{\alpha }{2}$