Explain giving examples the term 'colligative molality'. Why do we sometimes get abnormal molecular masses of the substances using colligative properties of the solution? The freezing point depression of `0.1` molal solution of benzoic acid in benzene is `0.526K`. For benzene `K_(f)` is `5.12K kg "mol"^(-1)`. Calculate the value of van't Hoff factor for benzoic acid in benzene. What conclusion can you draw about the molecular state of benzoic acid in benzene?

Explanation

The colligative properties like elevation in boiling point and depression in freezing point depend upon number of independent particals in solution tis is called colligative property
We get abnormal molecular mass if solute either undergoes association or dissociation.
`ul("Numerical problem")`
Given Molality of solution `=0.1m`
Freezing point depression `=0.526K`
Cryoscopic constant of benzne `=5.12K kg "mol"^(-1)`
Asked Van't hoff factor `=?`
Formulae: `DeltaT_(f)=ixxK_(f)xxm`
Explanation: `DeltaT_(f)=` Freezing point depression, `K_(f)=` cryoscopic constatant
`m=` molality of solution, `i=` Van't hoff factor
Substitution `&` Calculation
`0.256=ixx5.12xx0.1`
`i=(0.256)/(0.512)=(1)/(2)`