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  4. When 45 g of solute is dissolved in 600 g water, freezing point gets lowered by 2.2 K, calculate molar mass of solute. (Kf = 1.86 K kg mol-1)

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Q. When 45 g of solute is dissolved in 600 g water, freezing point gets lowered by 2.2 K, calculate molar mass of solute. $(K_f\, =\, 1.86\, K\, kg\, mol^{-1}$)

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Solution:

$w_{1}$ = 600 g,$\quad\quad\quad\Delta T_{f}$ = 2.2 K
$w_{2}$ = 45 g,$\quad\quad\quad\,\,K_{f}$ = 1.86 K kg mol$^{-1}$
M = $\frac{K_{f} \times w_{2}}{\Delta T_{f} \times w_{1}}=\frac{1.86\times45\times1000}{2.2\times600}=63.4 g mol^{-1}$