A solution of 0.450 g of urea (mol. wt. 60) in 22.5 g of water showed $0{.170}^{\mathrm{o}}\mathrm{C}$ of elevation in boiling point. Calculate the molal elevation constant of water. 

Weight of solute, w = 0.450 g

Weight of solvent, W = 22.5 g

Molecular weight of solute, m = 60

Molal elevation constant ${\mathrm{K}}_{\mathrm{b}}=?$

Boiling point elevation, ${\mathrm{\Delta T}}_{\mathrm{b}}=0{.170}^{\mathrm{o}}\mathrm{C}$

Substituting these values in the equation ${\mathrm{K}}_{\mathrm{b}}=\frac{\mathrm{m}\times \mathrm{W}\times {\mathrm{\Delta T}}_{\mathrm{b}}}{1000\times \mathrm{w}}$

                                                                           $=\frac{60\times 22.5\times 0.170}{1000\times 0.450}=0{.51}^{\mathrm{o}}\mathrm{C}$