Q28 / 155 · WBJEE 2017 · Chemistry
Assuming the compounds to be completely dissociated in aqueous solution, identify the pair of the solutions that can be expected to be isotonic at the same temperature.
- A$0.01 \mathrm{M}$ urea and $0.01 \mathrm{M} \mathrm{NaCl}$
- B$0.02 \mathrm{M} \mathrm{NaCl}$ and $0.01 \mathrm{M} \mathrm{Na}_{2} \mathrm{SO}_{4}$
- Correct answerC0.03 M $\mathrm{NaCl}$ and $0.02 \mathrm{M} \mathrm{MgCl}_{2}$
- D$0.01 \mathrm{M}$ sucrose and $0.02 \mathrm{M}$ glucose
Solution
$\because$ For Isotonic solution
$$
\pi_{1}=\pi_{2} \text { i.e. } i_{1} C_{1} R T=i f_{2} R T
$$
For option $(c)$
$$
\begin{array}{l}
i_{1}=2, i_{2}=3 \\
C_{1}=0.03 \\
C_{2}=0.02
\end{array}
$$
Thus, $\quad i_{1} \times C_{1}=i_{2} \times C_{2}$
Hence, are isotonic, i.e.
$$
0.06=0.06
$$
In all other options, $i_{1} \times C_{1} \neq i_{2} \times C_{2}$ Thus, are not isotonic.
Hence, the correct answer is option: 'C'.