Question

$30\, cc$ of $\frac {M}{3}\, HCl, 20\, cc$ of $\frac {M}{N} HNO_3$ and $40\, cc$ of $\frac {M}{4}$ $NaOH$ solutions are mixed and the volume was made up to $1\, dm^3$. The $pH$ of the resulting solution is

• A. 1
• B. 3
• C. 8
• D. 2

Answer 1

Answer: (D)

Total milliequivalents of $H ^{+}$

$=30 \times \frac{1}{3}+20 \times \frac{1}{2}=20$

Total milliequivalents of $OH ^{-}$

$=40 \times \frac{1}{4}=10$

Milli equivalence of $H ^{+}$ left

$=20-10=10$

$\therefore \,\,\,\,\,\left[ H ^{+}\right]=\frac{10}{1000} g \text { ions } / dm ^{3}=10^{-2} $

$\therefore \,\,\,\,\, pH =2$