Some Basic Concepts of Chemistry - Result Question 7 — JEE PYQ Chapterwise

Answer:

Correct Answer: 7. (b)

Solution: The reaction of HCl with $\mathrm{Na}_2 \mathrm{CO}_3$ is as follows:

$ 2 \mathrm{HCl}+\mathrm{Na}_2 \mathrm{CO}_3 \longrightarrow 2 \mathrm{NaCl}+\mathrm{H}_2 \mathrm{O}+\mathrm{CO}_2 $

We know that, $M_{\text {eq }}$ of $\mathrm{HCl}=M_{\text {eq }}$ of $\mathrm{Na}_2 \mathrm{CO}_3$

$ \begin{aligned} \dfrac{25}{1000} \times 1 \times M_{\mathrm{HCl}} & =\dfrac{30}{1000} \times 0.1 \times 2 \\ M_{\mathrm{HCl}} & =\dfrac{30 \times 0.2}{25}=\dfrac{6}{25} \mathrm{M} \end{aligned} $

The reaction of HCl with NaOH is as follows:

$ \mathrm{NaOH}+\mathrm{HCl} \longrightarrow \mathrm{NaCl}+\mathrm{H}_2 \mathrm{O} $

Also, $\mathrm{M}{\mathrm{eq}}$ of $\mathrm{HCl}=\mathrm{M}{\mathrm{eq}}$ of NaOH

$ \begin{aligned} \dfrac{6}{25} \times 1 \times \dfrac{V}{1000} & =\dfrac{30}{1000} \times 0.2 \times 1 \\ V & =25 \mathrm{~mL} \end{aligned} $