Question

Cyclohexane has a freezing point of 6.50 ∘C and a Kf of 20.0 ∘C/m. What is the freezing point of a solution made by dissolving 0.694 g of biphenyl (C12H10) in 25.0 g of cyclohexane?

Answer 1

The freezing point will be
`2.9^(0)C`

Step-by-step explanation:

The depression in freezing point is a colligative property.

It is related to molality as:

`Depressioninfreezing point=K_(f)Xmolality`

Where

Kf=
`20(^(0)C)/(m)`

the molality is calculated as:

`molality=(moles_(solute))/(mass_(solvent))`

`moles=(mass)/(molarmass)=(0.694)/(154)=0.0045mol`

`massofcyclohexane=25g=0.025Kg`

`molarity=(0.0045)/(0.025)=0.18m`

Depression in freezing point =
`20X0.18=3.6^(0)C`

The new freezing point =
`6.5^(0)C-3.6^(0)C=2.9^(0)C`