Calculating The Molar Mass of The Unknown Compound From Boiling Point Elevation
4.20g of an unknown compound is dissolved in 120.0g of benzene. The boiling temperature of the solution is 86.60˚C. The boiling temperature of pure solvent, benzene, is 80.10˚C; Kb = 2.53˚C/m. Calculate the molar mass of the unknown compound.
Change in the temperature, ΔTf = Tsolution – Tsolvent = 86.60 – 80.10 = 6.50˚C
Apply the boiling point elevation formula;
ΔTf = i. kb x (w/M) x (1000/W)
ΔTf = Boiling point elevation, i – Van’t Hoff factor, w- mass of solute (g), M – molar mass of non-volatile solute (g/mole), W – mass of solute (g)