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Q.
Mole fraction of a non-electrolyte in aqueous solution is $0.07$. If $K_{f}$ is $1.86^{\circ}C\, mol^{-1}\, kg$, depression in f.p t or $\Delta T_{f}$) is
Solutions
Solution:
Firstly we have to convert mole fraction into molality.
Molality $= \frac{x_{\text{solute}}}{x_{\text{solvent}} M_{\text{solvent}} 1000}$
$ = \frac{0.07 \times 1000}{0.93 \times 18} = 4.18$
Now, $\Delta T_{f} = K_{f}m = 1.86 \times 4.18 = 7.78^{\circ}C$