Question 13.4.6: In a laboratory experiment, a student found that a solution ......
In a laboratory experiment, a student found that a solution consisting of 0.315 g of an unknown compound (a nonvolatile nonelectrolyte) and 25 g of CHCl_{3} has a boiling point of 62.09 °C. The normal boiling point of CHCl_{3} is 61.70 °C. What is the molar mass of the compound? (Kbp = 3.63 °C/m for CHCl_{3})
You are asked to calculate the molar mass of a compound.
You are given the boiling point of the solvent and the solution and the mass of the solute and solvent.
Use the boiling point of the pure liquid and the solution to calculate the molality of the solute.
ΔT_{bp} = K{bp}m_{solute}i
(62.09 – 61.70) °C = (3.63 °C/m)(m_{solute})(1)
m_{solute} = 0.107 m
Use the molality and the mass of solvent to calculate moles of solute.
\frac{0.107\text{ mol solute}}{\text{kg CHCl}_{3}} \times 0.025 \text{ kg CHCl}_{3} = 0.00269 mol solute
Use the mass of solute and the moles of solute calculated above to calculate molar mass.
molar mass = \frac{0.315\text{ g}}{0.00269\text{ mol}} = 117 g/mol