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Q.
What is the $pH$ of a mixture obtained by mixing $75\,ml\,M / 5\, HCl$ and $25\, ml\, M / 5 \,NaOH$ aqueous solution?
Equilibrium
Solution:
Number of meq of $HCl =75 \times \frac{1}{5}=15$
Number of meq of $NaOH =25 \times \frac{1}{5}=5$
Number of meq of HCl left $=15-5$
$=10$ in $100\, ml$ soln.
$\left[ H ^{+}\right]=\frac{\text { Numbers of meq } HCI }{\text { Volume of solution }( ml )}$
$=\frac{10}{100}=10^{-1}$
$pH =1 .$