Q10 / 160 · TS EAMCET 2008 · Chemistry

$50 \mathrm{~mL}$ of $\mathrm{H}_2 \mathrm{O}$ is added to $50 \mathrm{~mL}$ of $1 \times 10^{-3} \mathrm{M}$ barium hydroxide solution. What is the $\mathrm{pH}$ of the resulting solution?

  • A
    $3.0$
  • B
    $3.3$
  • Correct answer
    C
    $11.0$
  • D
    $11.7$

Solution

In water, barium hydroxide is hydrolysed as follows. $$ \begin{aligned} \mathrm{Ba}(\mathrm{OH})_2 \rightleftharpoons & \mathrm{Ba}^{2+}+2 \mathrm{OH}^{-} \\ \text {conc. of } \mathrm{Ba}^{2+} & =1 \times 10^{-3} \mathrm{M} \\ \text { conc. of }\left[\mathrm{OH}^{-}\right] & =2 \times 1 \times 10^{-3} \mathrm{M} \\ & =2 \times 10^{-3} \mathrm{M} \\ \text { pOH } & =-\log \left[\mathrm{OH}^{-}\right] \\ & =-\log \left(2 \times 10^{-3}\right) \\ & =2.69 \end{aligned} $$ $\begin{aligned} \mathrm{pH}+\mathrm{pOH} & =14 \\ \mathrm{pH} & =14-\mathrm{pOH} \\ & =14-2.69 \\ & =11.3 \\ & \approx 11.0\end{aligned}$

Hence, the correct answer is option: 'C'.

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