CHM120H5 Lecture Notes - Lecture 1: Freezing-Point Depression, Vapor Pressure, Boiling-Point Elevation
Document Summary
Determination of a molar mass by freezing point depression. Determination of the molar mass is usually one of the first experiments attempted on unknown compounds. There are a variety of ways to do this, but the technique used in this experiment is based on a colligative property of solutions. A colligative property is one that depends primarily on the number of molecules in a solution and not on the nature of the molecules. These include vapour pressure lowering, boiling point elevation and freezing point depression, the latter of which will be employed in this experiment. When a non-volatile solute is dissolved in a solvent, the equilibrium vapour pressure of the resultant solution is always less than the equilibrium vapour pressure of the pure solvent. This lowering of the vapour pressure shows that there is a lesser tendency for the solvent molecules to escape into the vapour phase in the presence of dissolved solute.
