The boiling point of a solution containing 5.0 g of non-volatile solute in 1 kg of a solvent at `0.05^(@)` higher than that of poure solvent. Calculate the molecular mass of the solute (Molecular mass and `K_(b)` for a solvent are 78 and 2.53 K kg/`mol^(-1)` respectively).

Explanation

Given, `w_("solute") = 5.0 g`
`w_("solvent") = 1 kg`
`Delta T_(b) = 0.05^(@)C`
According to elevation in boiling point, we have
`M_("solute") = (K_(b) xx w_("solute"))/(Delta T_(b) xx W_("solvent") "(in kg)")`
`= (2.53 K kg/mol xx 5.0 g)/(0.05 xx 1kg)`
`= 253 g mol^(-1)`
Thus, molecular mass of the solute is `253 g mol^(-1)`.