1. Tardigrade
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  3. Chemistry
  4. The freezing point of water is depressed by 0.37° C in a 0.01 molal NaCl solution. The freezing point of 0.02 molal solution of urea is depressed by

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Q. The freezing point of water is depressed by $0.37^{\circ} C$ in a $0.01$ molal NaCl solution. The freezing point of $0.02$ molal solution of urea is depressed by

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Solution:

As we know that,
$\Delta t_{f}=i k_{j} m$
where, $\Delta t_{f}=$ depression in freezing point
$i =$ van't - Hoff factor
$m$= molality
and $k_{f}=$ freezing point depression constant.
For $0.01$ molal $NaCl$ solution
$0.37 =2 \times k_{f} \times 0.01$
$\therefore k_{f} =\frac{0.37}{2 \times 0.01}$ ...(i)
For $0.02$ molal urea solution
$\Delta t_{f}=1 \times k_{f} \times 0.02$
$\therefore k_{f}=\frac{\Delta t_{f}}{0.02}$ ...(ii)
From Eqs (i) and (ii)
$\frac{0.37}{2 \times 0.01} =\frac{\Delta t_{f}}{0.02}$
$\Delta t_{f} =\frac{0.37 \times 0.02}{2 \times 0.01}$
$\therefore \Delta t_{f} =0.37^{\circ} C$