Question

Choose the correct statement(s) :
(Assume 100% ionisation)

• A. $\text{Van't Hoff factor for}KCl(aq.)\text{is}2$
• B. $\text{Van't Hoff factor for}{K}_{2}S{O}_4(aq.)\text{is}3$
• C. $\text{Van't Hoff factor for}{K}_{2}S{O}_4(aq.)\text{is}2$
• D. $\text{Van't Hoff factor for}KCl(aq.)\text{is}0.5$

Answer 1

Answer: (A), (B)

$\text{Van't Hoff factor for}{K}_{2}S{O}_4(aq.)\text{is}3$

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

For $KCl$:
$KCl(aq.)\to 1K^{+}+1C{l}^{-}$
$i=2$

$K_{2}S{O}_4(aq.)\to 2K^{+}+1S{O}_4^{2-}$
$i=3$

Options (a) and (d) are correct.
Theory :
Affect of dissociation :

1. No of solute particles increase
2. Colligative property (CP) increases
3. Molar mass (MM) of solute decreases
   Hence, Observed MM < Expected MM