Chemical And Ionic Equilibrium Result Question 53
53. $0.1$ $ \mathrm{M}$ of $\mathrm{H} A$ is titrated with $0.1$ $ \mathrm{M} $ $\mathrm{NaOH}$, calculate the $\mathrm{pH}$ at end point. Given, $K _a(\mathrm{H} A)=5 \times 10^{-6}$ and $\alpha « 1$.
(2004)
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Answer:
Correct Answer: 53. $( 9 )$
Solution:
- At the end-point, $\left[A^{-}\right]=0.05$
$ \begin{aligned} K_b\left(A^{-}\right) & =K_w / K_a=2 \times 10^{-9} \\ {\left[\mathrm{OH}^{-}\right] } & =\sqrt{K_b \mathrm{C}}=\sqrt{2 \times 10^{-9} \times 0.05}=10^{-5} \\ \mathrm{pOH} & =5 \text { and } \mathrm{pH}=9 \end{aligned} $
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