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A chemist dissolves 0.38 g of an unknown non-electrolyte in 15.0 g of camphor…

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A chemist dissolves $0.38\ \text{g}$ of an unknown non-electrolyte in $15.0\ \text{g}$ of camphor. The melting point of the camphor falls by $6.6\ \text{K}$ . The constant for camphor is $K_f = 39.7\ \text{K kg/mol}$ . Find the molality of the solution and the molar mass of the solute.

Need a reminder? The key ideaShow

A colligative property depends on the number of solute particles. For a dilute solution, $\Delta T_b = K_b\,m$ and $\Delta T_f = K_f\,m$ , where $m$ is in mol/kg. For water, $K_b = 0.512\ \text{K kg/mol}$ and $K_f = 1.86\ \text{K kg/mol}$ . The molar mass is $M_2 = \dfrac{1000\,K\,w_2}{\Delta T\,w_1}$ , with the masses in grams.

The worked solution

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