Question

Millimoles of calcium hydroxide required to produce $100\, mL$ of the aqueous solution of $pH 12$ is $x \times 10^{-1}$. The value of $x$ is ___(Nearest integer). Assume complete dissociation.

Answer 1

$ \because pH =12 $
$ \therefore\left[ H ^{+}\right]=10^{-12} M$
$ \therefore[ OH ]=10^{-2} M $
$ \therefore\left[ Ca ( OH )_2\right]=5 \times 10^{-3} M $
$5 \times 10^{-3}=\frac{\text { milli moles of } Ca ( OH )_2}{100 mL } $
$\text { milli moles of } Ca ( OH )_2=5 \times 10^{-1}$
$ \text { Ans. }=5$