Question

$20mL$ of $1MHCl$ is titrated against the $1MNaOH$ solution. Calculate the $pH$ of the solution when $30mLNaOH$ is added?

• A. 0.7
• B. 13.3
• C. 12.6
• D. 2

Answer 1

The correct option is B 13.3

mmol of $HCl=20\times 1=20$
mmol of $NaOH\text{added}=30\times 1=30$

$HCl\left(aq\right)+NaOH\left(aq\right)\to NaCl\left(aq\right)+H_{2}O\left(l\right)Initial:203000Final:0102020$

After titration total $HCl$ will react and excess $NaOH$ is present in the solution.
mmol of $NaOH$ remaing $=10$
$\text{Final concentration}=\frac{\text{Moles of NaOH remaining}}{\text{Total Volume}}$
Total Volume $=30+20=50mL$
$[NaOH{]}_{final}=\frac{10}{50}M=0.2MpOH=-\log [O{H}^{-}]pOH=-\log [0.2]pOH=1-\log (2)=0.7pH=14-0.7=13.3$