Solution: Determine the required concentration (in percent by mass) for an aqueous ethylene glycol (C2H6O2) solution to have a boiling point of 107.1 oC.

Problem

Determine the required concentration (in percent by mass) for an aqueous ethylene glycol (C2H6O2) solution to have a boiling point of 107.1 oC.

Solution

We’re being asked to calculate the mass percent of ethylene glycol (C2H6O2) solution to have a boiling point of 107.1 oC.


Recall that the boiling point of a solution is higher than that of the pure solvent and the change in boiling point (ΔT­b) is given by:


Tb = Tb, solution - Tb, pure solvent 


The change in boiling point is also related to the molality of the solution:


Tb = iKbm


where: 

i = van’t Hoff factor

m = molality of the solution (in m or mol/kg)

Kb = boiling point elevation constant (in ˚C/m)


Recall that the molality of a solution is given by:


Molality (m) = moles of soluteKilograms of solvent


We go through the following steps to solve:

Step 1. Calculate the molality

Step 2. Calculate the mass of solute and solvent

Step 3. Calculate the mass percent


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