A 4.305-g sample of a nonelectrolyte is dissolved in 105 g of water. the solution freezes at -1.23c. calculate the molar mass of the solute.
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Answers ( 1 )
The answer is 62.00 g/mol.
Solution:
Knowing that the freezing point of water is 0u00b0C, temperature change u0394t is
u0394t = 0C – (-1.23u00b0C) = 1.23u00b0C
Since the van ‘t Hoff factor i is essentially 1 for non-electrolytes dissolved in water, wecalculate for the number of moles x of the compound dissolved from the equation
u0394t = i Kf m
1.23u00b0C = (1) (1.86u00b0C kg mol-1) (x / 0.105 kg)
x = 0.069435 mol
Therefore, the molar mass of the solute is
molar mass = 4.305g / 0.069435mol = 62.00 g/mol