Question

Find the $pH$ of solution prepared by mixing $25 \,ml$ of a $0.5\, M$ solution of $HCl , 10 \,ml$ of $a 0.5\, M$ solution of $NaOH$, and $15 \,ml$ of water.

• A. 0.8239
• B. 1.0029
• C. 1.0239
• D. 1.8239

Answer 1

Answer: (A)

We know that for $HCl$ and $NaOH$, m.e. = milli equivalent

$\therefore $ m.e. of $HCl=0.5 \times 25=12.5$

m.e. of $NaOH =0.5 \times 10=5.0$

m.e. of $HCl$ in the resultant mixture

$=12.5-5.0=7.5$

Total volume $= (25 + 10 + 15) \,ml = 50 \,ml$

$\therefore $ Normality of $HCl =\frac{\text { m.e. }}{\text { Vol (ml) }}=\frac{7.50}{50}$

$\therefore $ Molarity $=\frac{7.50}{50}$

$\therefore {\left[ H ^{+}\right]=[ HCl ]=\frac{7.50}{50}} $

$ \therefore pH =-\log \frac{7.50}{50}=0.8239 $