Q8 / 160 · AP EAMCET 2013 · Chemistry

Which one of the following is an isotonic pair of solutions?

  • Correct answer
    A
    $0.15 \mathrm{M} \mathrm{NaCl}$ and $0.1 \mathrm{M} \mathrm{Na}_2 \mathrm{SO}_4$
  • B
    $0.2 \mathrm{M}$ Urea and $0.1 \mathrm{M}$ Sugar
  • C
    0.1 $\mathrm{MBaCl}_2$ and $0.2 \mathrm{M}$ Urea
  • D
    $0.4 \mathrm{M} \mathrm{MgSO}_4$ and $0.1 \mathrm{MNH}_4 \mathrm{Cl}$

Solution

Two solutions are isotonic if they have same molar concentrations of the particles. (a) $0.15 \mathrm{M} \mathrm{NaCl}$ and $0.1 \mathrm{M} \mathrm{Na}_2 \mathrm{SO}_4$ $\mathrm{NaCl}$ is an electrolyte which dissociates to give 2 ions, thus concentration of ions in the solution $0.30 \mathrm{M}$. Similarly for $\mathrm{Na}_2 \mathrm{SO}_4$ (3 ions), the concentration of ions in the solution $=0.30 \mathrm{M}$. Hence, both are isotonic.

Hence, the correct answer is option: 'A'.

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