Molar Mass of Solute from Freezing Point Depression

Refer to Eq. (2.17), $\Delta T_f = K_f m$. The molality $m$ of the solution is given by Eq. (2.14) as

Substitution of Eq. (2.14) into Eq. (2.17) gives

Hence,

$M_2 = \frac{1000\,K_f W_2}{\Delta T_f W_1} \qquad \text{...(2.18)}$ …