of () and of () are mixed at to form a solution of density . Calculate the approximate theoretical f — Solutions and Colligative Properties Chemistry Question
Question
$30\text{ mL}$ of $CH_3OH$ ($d = 0.798\text{ g cm}^{-3}$) and $70\text{ mL}$ of $H_2O$ ($d = 0.9984\text{ g cm}^{-3}$) are mixed at $25^\circ\text{C}$ to form a solution of density $0.9575\text{ g cm}^{-3}$. Calculate the approximate theoretical freezing point of the solution ($K_f = 1.86$).
Answer: A
💡 Solution & Explanation
Mass of $CH_3OH = 30 \times 0.798 = 23.94\text{ g}$. Mass of $H_2O = 70 \times 0.9984 = 69.888\text{ g}$. Moles $CH_3OH = 23.94 / 32 = 0.748\text{ mol}$. Molality $m = \frac{0.748}{0.069888\text{ kg}} = 10.70\text{ m}$. $\Delta T_f = 1.86 \times 10.70 = 19.9^\circ\text{C}$. Freezing point $= -19.9^\circ\text{C}$.
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