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Q.
Find the $pH$ value of the mixture containing $50\, cc\, M\, HCl$ and $30\, cc\, M\, NaOH$ solution, assuming both to be completely ionised.
ManipalManipal 2017
Solution:
Total volume after mixing $=50+30=80\, cc$
Moles of $HCl$ after mixing $=\frac{50}{80} M$
Moles of $NaOH$ after mixing $=\frac{30}{80} M$
Remaining number of moles of $HCl$ after mixing
$=\frac{50}{80}-\frac{30}{80}=0.25\, M$
$\left[H^{+}\right]=0.25=2.5 \times 10^{-1}$
$pH =-\log \left[2.5 \times 10^{-1}\right]=1-0.3979=0.6021$