Question

Assuming equal concentrations and complete dissociation, rank these aqueous solutions by their freezing points. nh4cl na3po4 li2so4

Answer 1

By using the formula of depression in freezing, it can easily identify the rank of the given compounds.

`\Delta T= i.K_(f).m`

where,

`\Delta T` = freezing point depression

i = van 't Hoff factor (number of ions per individual molecule of solute)

m = molality of the solute

`K_(f)` = molal freezing point

According to question, if concentration (m) and
`K_(f)` is same, then only van 't Hoff factor will change.

For
`NH_(4)Cl`, i = 2

For
`Na_(3)PO_(4)`, i = 4

For
`Li_(2)SO_(4)`, i= 3

Now, the solute with the largest i value results in low freezing point.

The highest value of i is 4 (
`Na_(3)PO_(4)`), thus
`Na_(3)PO_(4)` has lowest freezing point.

And,
`NH_(4)Cl` has highest freezing point.

The order of freezing point is :
`NH_(4)Cl> Li_(2)SO_(4)> Na_(3)PO_(4)`