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Question: Answered & Verified by Expert
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.
ChemistrySolutionsWBJEEWBJEE 2017
Options:
  • A $0.01 \mathrm{M}$ urea and $0.01 \mathrm{M} \mathrm{NaCl}$
  • B $0.02 \mathrm{M} \mathrm{NaCl}$ and $0.01 \mathrm{M} \mathrm{Na}_{2} \mathrm{SO}_{4}$
  • C 0.03 M $\mathrm{NaCl}$ and $0.02 \mathrm{M} \mathrm{MgCl}_{2}$
  • D $0.01 \mathrm{M}$ sucrose and $0.02 \mathrm{M}$ glucose
Solution:
1435 Upvotes Verified Answer
The correct answer is: 0.03 M $\mathrm{NaCl}$ and $0.02 \mathrm{M} \mathrm{MgCl}_{2}$
$\because$ 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.

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