Calculate the freezing point of a solution containing 8.1 g of HBr in 100g of water, assuming the acid to be 90% ionized. [Given : Molar mass Br = 80 g/mol, `K_(f)` water = 1.86 K kg/mol].

Explanation

HBr dissociates in aqueous solution as:
`HBrtoH^(+)+Br^(-)`
`"Van't Hoff facttor (i)"=alpha (n-1)+1=0.9(2-1)+1=1.9`
`DeltaT_(f)=ixxK_(f)xxm=(ixxK_(f)xxW_(B))/(M_(B)xxW_(A))`
` i=1.9, `K_(f)=1.86 K kg mol^(-1), W_(B)=8.1 g, W_(A)=0.1 kg: M_(B)=81 g mol^(-1)`
`DeltaT_(f)=((1.9)xx(1.86 K kg mol^(-1))xx(8.1 g))/((81 g mol^(-1))xx(0.1 kg))-3.534 K`
Freezing point of the solution `(T_(f)=T_(f)^(@))-DeltaT_(f)=(273 K-3.534)=269.466 K`