15.6 g of an unknown molecular solute is dissolved in 5.02 moles of ethanol (C2H5OH), causing...
15.6 g of an unknown molecular solute is dissolved in 5.02 moles of ethanol (C2H5OH), causing the freezing point of ethanol to decrease by 1.14 °C. Calculate the molar mass of the solute. For ethanol, the molar mass is 46.07 g/mol and Kf = 1.99 °C/m.
Homework Answers
T = Kf × m
Kf = 1.99℃/m
m = molality = moles of solute / kg of solvent
We know moles = mass / molar mass
Mass of ethanol = 5.02 × 46.07 = 231.27 g = 0.2313 kg
Moles of solute = (∆T/Kf) × mass of solvent in kg = (1.14/1.99) × 0.2313 = 0.1325 mole
Molar mass of solute = mass in g / moles = 15.6 / 0.1325 = 117.74 g/mol
Thus answer: molar mass of solute = 117.74 g/mol
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