What is the freezing point (in ) of a solution containing of (Molecular weight ) completely dissolve — Solutions and Colligative Properties Chemistry Question
Question
What is the freezing point (in $^\circ\text{C}$) of a solution containing $0.1\text{ g}$ of $K_3[Fe(CN)_6]$ (Molecular weight $329$) completely dissolved in $100\text{ g}$ of water? ($K_f = 1.86\text{ K kg mol}^{-1}$, assume $100\%$ ionization).
Answer: A
💡 Solution & Explanation
$K_3[Fe(CN)_6]$ yields 4 ions ($3K^+ + [Fe(CN)_6]^{3-}$), so $i=4$. Molality $m = \frac{0.1/329}{100/1000} = \frac{1}{329}\text{ m}$. $\Delta T_f = i \times K_f \times m = 4 \times 1.86 \times \frac{1}{329} = \frac{7.44}{329} \approx 0.0226^\circ\text{C}$. Freezing point $= -2.26 \times 10^{-2} \approx -2.3 \times 10^{-2} ^\circ\text{C}$.
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