Question

Calculate the resultant $pH$ of a solution when $20$ ml of $0.1N$ $NaOH$ os mixed with $20$ ml of $0.05M$ $Ca{\left(OH\right)}_2$ at ${25}^{o}C$.

• A. $1$
• B. $2$
• C. $13$
• D. $14$

Answer 1

The correct option is C $13$

At ${25}^{o}CpH+pOH=14$
Resultant pH of a solution when $20ml$ of $0.1N$ $NaOH$ os mixed with $20ml$ of $0.05M$ $Ca{\left(OH\right)}_2$
moles $Ca(OH{)}_2=0.05M\times 0.02L=0.001$ moles $O{H}^{-}=0.001\times 2=0.002mole$
moles $NaOH=0.020L\times 0.1M=0.0020$ moles $O{H}^{-}=0.0020$
total moles $O{H}^{-}=0.002+0.002=0.004$
total volume = 0.040L $\left[O{H}^{-}\right]=0.004/0.040=0.1mole{L}^{-1}$
pOH = $-log\left[O{H}^{-}\right]=-log\left[{10}^{-1}\right]=1$
$pH=14-pOH=14-1=13$