What is the molar mass of toluene if 0.85 g of toluene depresses the freezing point of 100.g of benzene by 0.47°C? K_f of benzene is 5.12°C/m. A)927 g/mol B)92.6 g/mol C)81.8 g/mol D)78.0 g/mol E)10.7 g/mol

Question

Quizplus · Accepted Answer

First, find the molality of the solution:
molality = (0.85 g toluene / 92.14 g/mol toluene) / (100 g benzene / 78.11 g/mol benzene) = 0.0122 mol/kg

Next, use the freezing point depression equation:
ΔTf = Kf * molality
0.47°C = 5.12°C/m * 0.0122 mol/kg
Molar mass of toluene = (0.47°C / 5.12°C/m) * (100 g benzene / 78.11 g/mol benzene) / 0.85 g = 92.6 g/mol

Therefore, the correct answer is B.

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