When of a non-volatile, non-electrolyte solute is dissolved in of pure water, the relative lowering — Solutions and Colligative Properties Chemistry Question
Question
When $12\text{ g}$ of a non-volatile, non-electrolyte solute is dissolved in $108\text{ g}$ of pure water, the relative lowering of vapour pressure is observed to be exactly $0.1$. Using the dilute solution approximation, calculate the molecular mass of the solute.
Answer: B
💡 Solution & Explanation
$RLVP = \frac{n_{solute}}{n_{solvent}} = 0.1$. Moles of water $N = 108/18 = 6\text{ moles}$. Solute moles $n = 12/M$. Thus, $\frac{12/M}{6} = 0.1 \implies \frac{2}{M} = 0.1 \implies M = 20\text{ g mol}^{-1}$.
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