Chemistry II boiling point of solution

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 12.1 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

Adding a solute to a pure solvent raise the boiling point of the pure solvent. To find the change in the boiling point, use ∆T = imK. See colligative properties.

∆T = change in the boiling point

i = van't Hoff factor = 1 for glucose (a non electrolyte)

m = molality = moles glucose / kg ethanol (see below)*

K = boiling constant for pure ethanol = 1.22ºC/m

*Finding molality of solution:

moles glucose = 12.1 g glucose x 1 mol / 180.16 g = 0.06717 moles

kg of ethanol = 100.0 g ethanol x 1 kg / 1000 g = 0.10000 kg

molality = 0.06717 mols / 0.10000 kg = 0.6717 m

∆T = (1)(0.6717)(1.22)

∆T = 0.819º

New boiling point of the solution = 78.4º + 0.819º = 79.2ºC