Question

Choose the correct statement(s) :
(Assume complete dissociation/association)

• A. $\text{Van't Hoff factor for}Ba\left(OH{)}_2\right(aq.)\text{is}2$
• B. $\text{Van't Hoff factor for}Ba\left(OH{)}_2\right(aq.)\text{is}3$
• C. $\text{Van't Hoff factor for}C{H}_{3}COOH\text{in benzene is}2$
• D. $\text{Van't Hoff factor for}C{H}_{3}COOH\text{in benzene is}0.5$

Answer 1

Answer: (B), (D)

$\text{Van't Hoff factor for}C{H}_{3}COOH\text{in benzene is}0.5$

$\text{van't Hoff factor}\left(i\right)=\frac{\text{Number of molecules (actual)}}{\text{Number of molecules (expected)}}$

$Ba(OH{)}_2$ is a strong electrolyte soits 100% dissociation occurs in an aqueous solution.

$Ba(OH{)}_2\to B{a}^{+2}+2O{H}^{-}$
$i=3$

Molecules of ethanoic acid dimerise in benzene due to hydrogen bonding. This normally happens in solvents of low dielectric constant. In this case number of particles are reduced due to dimerisation.
Association of molecules is depicted as follows:

Here $i=0.5$
Option (a) and (d) are correct
Theory :
Effect of Association

1. No of solute particles decrease
2. Colligative property (CP) decreases
3. Molar mass (MM) of solute increases
   Observed MM > Expected MM