When a 49.1-g sample of an unknown compound is dissolved in 500.g of benzene,the freezing point of the resulting solution is 3.77°C.The freezing point of pure benzene is 5.48°C and K_f for benzene is 5.12°C/m.Calculate the molar mass of the unknown compound. A)147 g/mol B)28.7 g/mol C)251 g/mol D)588 g/mol E)294 g/mol

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Quizplus · Accepted Answer

The freezing point depression is calculated as ΔTf = 5.48°C - 3.77°C = 1.71°C. Using the formula ΔTf = Kf * m, where m is the molality, we find m = 1.71°C / 5.12°C/m = 0.334 mol/kg. The molality is moles of solute per kg of solvent, so moles of solute = 0.334 mol/kg * 0.500 kg = 0.167 mol. The molar mass is mass of solute / moles of solute = 49.1 g / 0.167 mol = 294 g/mol.

When a 491-G Sample of an Unknown Compound Is Dissolved in 500