## 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