First slide

Salt hydrolysis :

Question

Statement I : Aqueous solution of Na₂CO₃ shows pH > 7.
Statement II : Salt of strong base and weak acid undergoes anionic hydrolysis.

Easy

A

Statement I and II are correct
B

Statement I is correct and Statement II is incorrect
C

Statement - I is incorrect and Statement II is correct
D

Both statement - I and statement - II are False

Solution

P^H of an aqueous solution of salt of strong base and weak acid (Na₂CO₃) is given by
$P^{H} = \frac{1}{2} [P^{K_{w}} + P^{K_{a}} + logC] \Rightarrow P^{H} > 7$
Salt of strong base and weak acid undergoes anionic hydrolysis,
${Na}_{2} {CO}_{3} (aq) \to 2 {Na}^{+} (aq) + {CO}_{3}^{- 2} (aq)$
Na⁺ is a derivative of strong base and will not undergo hydrolysis.
$\underset{C_{o} - x}{{CO}_{3}^{- 2}} + H_{2} O ⇌ \underset{x - y}{{HCO}_{3}^{-}} + \underset{x + y}{{OH}^{-}}; K_{h_{1}} = \frac{K_{W}}{K_{a_{2}}}$
$\underset{x - y}{{HCO}_{3}^{-}} + H_{2} O ⇌ H_{2} {CO}_{3} + \underset{y + x}{{OH}^{-}}; K_{h_{2}} = \frac{K_{w}}{K_{a_{1}}}$
$K_{h_{1}} ≫ K_{h_{2}} \Rightarrow x ≫ y$
$K_{h_{1}} = \frac{K_{w}}{K_{a_{2}}} = \frac{(x - y) (x + y)}{C_{0} - x}$
$\Rightarrow \frac{K_{w}}{K_{a_{2}}} = \frac{x \times x}{C_{0}}$
$\Rightarrow x = \sqrt{\frac{C_{0} K_{w}}{K_{a_{2}}}}$
$\Rightarrow P^{OH} = \frac{1}{2} [P^{K_{w}} - P^{K_{a_{2}}} - {logC}_{0}]$
$\Rightarrow P^{H} = \frac{1}{2} [P^{K_{w}} + P^{K_{a_{2}}} + {logC}_{0}]$

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