Question

The colligative properties of electrolytes require a slightly diferent approach than the one used for the colligative properties of non- electrolytes. The electrolytes dissociate
into ions in solution. It is the number of solute particles that determine the colligative properties of a solution. The electrolyte solutions, therefore show abnormal colligative properties. To account for this effect we define a quantity; called the van't Hoff factor which is given by [solution]
$i= \frac{\text{Actual number of particles in solution after dissociation}}{\text{ Number of formula units initially dissolved in solution }}$
$i =1$ (for non - electrolytes);
$i >1$ (for electrolytes, undergoing dissociation)
$i < 1$ (for solute, undergoing association)
Benzoic acid undergoes dimerisation in benzene solution. The van't Hoff factor '$i$' is related to the degree of association ' $\alpha$ ' of the acid as

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

Answer 1

Answer: (D)

Correct answer is (d) $i=1-\frac{\alpha}{2}$