First slide

Ionization constants of weak bases, PH of weak bases

Question

Statement I : When 0.1M weak diprotic acid H₂A dissociates with its dissociation constants K_a1= 10^-3and K_a2 =10^-8
and , then [A^–2] is almost equal to 10^–3M.
Statement II : Since $K_{a_{2}} < < K_{a_{1}}$ for 0.1 M H₂A, so [A^–2] is considerable w.r.t. [HA^–].

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

$\underset{C_{0} - x}{H_{2} A} ⇌ \underset{x - y}{{HA}^{-}} + \underset{x + y}{H^{+}}; K_{a_{1}} = \frac{x \times x}{C_{0}}$
$\underset{x - y}{{HA}^{-}} ⇌ A_{y}^{- 2} + H_{y + x}^{+}; K_{a_{2}} = \frac{x \times y}{x}$
$K_{a_{1}} ≫ K_{a_{2}} \Rightarrow x ≫ y$
$\Rightarrow y = K_{a_{2}}$
$Also, C_{0} ≫ x$
$\Rightarrow [A^{- 2}] ≅ K_{a_{2}}$

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