Problem: A solution prepared by dissolving 3.27 g of a nonvolatile, covalent solute in 30.0 g of water boils at 100.74 °C. What is the approximate molar mass of the solute? K bp H 2O = 0.512 oC/m. 

FREE Expert Solution

We’re being asked to list the given aqueous solutions in order of increasing boiling points.


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:


ΔTb=Tb, solution-Tb, pure solvent


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


ΔTb=imKb


where: 

i = van’t Hoff factor

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

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


We go through the following steps to solve the problem:

Step 1. Calculate the molality of the solution

Step 2. Calculate the moles of solute

Step 3. Calculate the molar mass


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Problem Details

A solution prepared by dissolving 3.27 g of a nonvolatile, covalent solute in 30.0 g of water boils at 100.74 °C. What is the approximate molar mass of the solute? K bp H 2O = 0.512 oC/m. 

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What scientific concept do you need to know in order to solve this problem?

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