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Answer the following.
Calculate the mass of compound (molar mass = ) to be dissolved in of benzene to lower its freezing…
Calculate the mass of compound (molar mass = $256\text{ g mol}^{-1}$) to be dissolved in $75\text{ g}$ of benzene to lower its freezing point by $0\cdot48\text{ K}$ ($K_f = 5\cdot12\text{ K kg mol}^{-1}$).
Answer
Answer
AIFormula used: Depression of freezing point: dTf = i*Kf*m with Kf = 5.12 K kg mol^-1, M2 = 256 g mol^-1, w1 = 75 g, dTf = 0.48 K, so w2 = 1.8 g
Formula: $\Delta T_f = \dfrac{K_f \times w_2 \times 1000}{M_2 \times w_1}$
$0\cdot48 = \dfrac{5\cdot12 \times w_2 \times 1000}{256 \times 75}$
$w_2 = \dfrac{0\cdot48 \times 256 \times 75}{5\cdot12 \times 1000} = 1\cdot8\ \mathrm{g}$
Final answer: 1.8 g
From ISC 2018 Specimen Chemistry Paper 1, question 1(d)(i).
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