Question

A solution containing 2.5 g solute per 100 g benzene depresses the freezing point of
benzene by 1 K. Calculate the molar mass of the solute if Kf, for benzene is 5 K kg/mol
​

Answer 1

Answer:

Let M be the molecular weight of the compound.

Number of moles is the ratio of mass to molecular weight.

Number of moles of solute

M

2.40

Molality of solution is the number of moles of solute in 1000 g of water.

Molality =

M×60.0

2.40×1000

=

M

40

The depression in the freezing point =ΔT

f

=K

f

m

⟹0.10=5.12×

M

40

⟹M=2050g/mol