Question

$0.0005\text{mol}$ of strong electrolyte, $Ca(OH{)}_2$ is dissolved to form $100\text{mL}$ of a saturated aqueous solution. The $pH$ of this solution is:

• A. $12$
• B. $11.7$
• C. $9.78$
• D. $3.3$

Answer 1

The correct option is A $12$

$\text{The concentration of}Ca(OH{)}_2=\frac{0.0005\times 1000}{100}=0.005{\text{mol L}}^{-1}$
$$\begin{array}{cccccc}& Ca(OH{)}_2& \rightleftharpoons & C{a}^{2+}& +& 2O{H}^{-}\\ \text{Initially}& & & 1& & 2\\ & & & 0.005& & 0.005\times 2=0.01\end{array}$$
$pOH=-\log \left[O{H}^{-}\right]$
$pOH=-\log \left[0.01\right]=2\Rightarrow pH=14-2=12$