KCET · Chemistry · Ionic Equilibrium
\(30 \operatorname{cc}\) of \(\frac{\mathrm{M}}{3} \mathrm{HCl}, 20 \operatorname{cc}\) of \(\frac{\mathrm{M}}{2} \mathrm{HNO}_{3}\) and \(40 \mathrm{cc}\) of \(\frac{\mathrm{M}}{4} \mathrm{NaOH}\) solutions are mixed and the volume was made up to \(1 \mathrm{dm}^{3}\). The \(\mathrm{pH}\) of the resulting solution is
- A 8
- B 2
- C 1
- D 3
Answer & Solution
Correct Answer
(B) 2
Step-by-step Solution
Detailed explanation
Total milliequivalents of \(\mathrm{H}^{+}\)
\[
=30 \times \frac{1}{3}+20 \times \frac{1}{2}=20
\]
Total milliequivalents of \(\mathrm{OH}^{-}\)
\[
=40 \times \frac{1}{4}=10
\]
Milli equivalence of \(\mathrm{H}^{+}\)left
\[
\begin{gathered}
=20-10=10 \\
\therefore \quad\left[\mathrm{H}^{+}\right]=\frac{10}{1000} \text { g ions } / \mathrm{dm}^{3}=10^{-2} \\
\therefore \quad \mathrm{pH}=2
\end{gathered}
\]
\[
=30 \times \frac{1}{3}+20 \times \frac{1}{2}=20
\]
Total milliequivalents of \(\mathrm{OH}^{-}\)
\[
=40 \times \frac{1}{4}=10
\]
Milli equivalence of \(\mathrm{H}^{+}\)left
\[
\begin{gathered}
=20-10=10 \\
\therefore \quad\left[\mathrm{H}^{+}\right]=\frac{10}{1000} \text { g ions } / \mathrm{dm}^{3}=10^{-2} \\
\therefore \quad \mathrm{pH}=2
\end{gathered}
\]
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