Question

An aqueous solution contains 0.200 g of an unknown, non-ionic solute in 40.0 g of water. The solution freezes at – 0.060 °C. What is the molar mass of the solute? ( Kfp for H2O is −1.86 C/m.)

Molar mass = ____ g/mol

Answer 1

Answer :-

Molar mass of unknown = 155 g/mol

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Explanation :-

Given :-

Molar mass of unknown = M​​​​​​2 = ?

Mass of unknown W​​​​​2 = 0.2 g = 0.0002 kg

Mass of water = W​​​​​​1 = 40 g = 0.04 kg

K​​​​​​f = 1.86 °C/m = 1.86 °C.kg/mol

(since, m = mol/kg)

Freezing point of solution = T= ​- 0.06 °C

Freezing point of water = T° = 0 °C

Thus, Depression of freezing point ( ) is given by

i.e.

Formula :-

therefore,



I.e.

i.e.

i.e.

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