At T (K),if the ionisation constant of ammoni | vedclass

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Question

(B) For a weak base $NH_3$,the ionisation constant $K_b = 2.5 	imes 10^{-5}$.For the conjugate acid $NH_4^{+}$,the ionisation constant $K_a$ is given

Vedclass · Accepted Answer

$10.7, 4.0 	imes 10^{-10}$

Vedclass · Answer

(B) For a weak base $NH_3$,the ionisation constant $K_b = 2.5 	imes 10^{-5}$.For the conjugate acid $NH_4^{+}$,the ionisation constant $K_a$ is given by $K_a 	imes K_b = K_w = 10^{-14}$.$K_a = \frac{10^{-14}}{2.5 	imes 10^{-5}} = 4 	imes 10^{-10}$.For $0.01 \ M$ $NH_3$ solution,$[OH^{-}] = \sqrt{K_b 	imes C} = \sqrt{2.5 	imes 10^{-5} 	imes 0.01} = \sqrt{2.5 	imes 10^{-7}} = \sqrt{25 	imes 10^{-8}} = 5 	imes 10^{-4} \ M$.$pOH = -\log[OH^{-}] = -\log(5 	imes 10^{-4}) = 4 - \log 5 = 4 - 0.7 = 3.3$.$pH = 14 - pOH = 14 - 3.3 = 10.7$.Thus,the $pH$ is $10.7$ and the ionisation constant of the conjugate acid is $4 	imes 10^{-10}$.

At $T$ $(K)$,if the ionisation constant of ammonia in solution is $2.5 \times 10^{-5}$,the $pH$ of $0.01 \ M$ ammonia solution and the ionisation constant of its conjugate acid respectively at that temperature are $(\log 2 = 0.30)$

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