Consider the dissociation of the weak acid HX as given below:

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Solution

Q.
Consider the dissociation of the weak acid HX as given below:

$HX(aq) ⇌ H^{+} (aq) + X^{-} (aq), K a = 1.2 \times 10^{- 5}$

[ $K_{a}$ : dissociation constant]

The osmotic pressure of 0.03 M aqueous solution of HX at 300 K is ______ $\times 10^{- 2}$ bar (nearest integer).

[Given: R = 0.083 L bar ${mol}^{- 1}$ $K^{- 1}$ ] [2024]

Ans.
(76)

$HX(aq) ⇌ H^{+} (aq) + X^{-} (aq)$

$(t = 0)$ $C$

$(c o n c .)$

$(t = \infty)$ $C (1 - α)$    $C α$ $C α$

   $(c o n c .)$

   $K_{a} = \frac{C α^{2}}{1 - α} \approx C α^{2}$

$1.2 \times 10^{- 5} = 0.03 α^{2}$

   $α = \sqrt{\frac{1.2 \times 10^{- 5}}{0.03}} = 0.02$

$i = 1 + (n - 1) α = 1 + (2 - 1) \times 0.02 = 1.02$

$π = i C R T = 1.02 \times 0.03 \frac{mol}{L} \times 0.083 \frac{bar L}{mol K} \times 300 K = 76.2 \times 10^{- 2} bar$

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