Chemical And Ionic Equilibrium Result Question 11
11. $\mathrm{p} K _a$ of a weak acid $(\mathrm{H} A)$ and $\mathrm{p} K _b$ of a weak base $(\mathrm{BOH})$ are 3.2 and 3.4, respectively. The $\mathrm{pH}$ of their salt $(A B)$ solution is
(2017 Main)
(a) $7.2$
(b) $6.9$
(c) $7.0$
(d) $1.0$
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Answer:
Correct Answer: 11. ( b )
Solution:
- For a salt of weak acid and weak base,
$\mathrm{pH}=7+\frac{1}{2} \mathrm{pK}_a-\frac{1}{2} \mathrm{pK}_b$
Given, $\mathrm{p} K_{\mathrm{a}}(\mathrm{H} A)=3.2, \mathrm{p} K_a(B \mathrm{OH})=3.4$
$\begin{aligned} \therefore \quad \mathrm{pH} & =7+\frac{1}{2}(3.2)-\frac{1}{2}(3.4) \\ & =7+1.6-1.7=6.9 \end{aligned}$
BETA
