Question

The electrolyte solutions show abnormal colligative properties. To account for this effect we define a quantity called the Van't Hoff factor given by
Answer the following questions:
$i=\frac{\text{Actual number of particles in solution after dissociation }}{\text{ Number of formula units initially dissolved in solution}}$
$i=1$ (for non-electrolytes)
$i>1$ (for electrolytes, undergoing dissociation)
$i<1$ (for solutes, undergoing association)
Answer the following questions:
Benzoic acid undergoes dimerization in benzene solution. The Van't Hoff factor $i$ is related to the degree of association $\alpha$ of the acid as

• A. $i=2-\alpha$
• B. $i=1+(\alpha /3)$
• C. $i=1-(\alpha /2)$
• D. $i=1+(\alpha /2)$

Answer 1

Answer: (C)

$\therefore i=\frac{\text{ Total moles at equilibrium }}{\text{ Initial moles }}=1-\frac{\alpha }{2}$