Chemistry II Boiling Point Problem

Question

The boiling point of pure ethanol (C₂H₅OH, MM = 46.07 g/mol) is 78.4 °C. A solution is made using 100.0 g of ethanol (the solvent) and 25.1 g of glucose (MM = 180.16 g/mol). What is the boiling point of this solution, in °C? (Kb of ethanol is 1.22 °C/m)

Answer 1

Colligative Properties:

Boiling point elevation

∆T = imK

∆T = change in boiling point

i = van't Hoff factor = 1 for glucose since it does not ionize or dissociate

m = molality = moles glucose/kg ethanol = 25.1 g / 180.16 g/mol / 0.1 kg = 1.39 m

K = boiling constant for ethanol = 1.22º/m

Solving for ∆T we have...

∆T = (1)(1.39)(1.22) = 1.70ºC

New boiling point of the solution = 46.07º + 1.70º = 47.77ºC