Chemistry · Ch 1 — Solutions
Colligative Properties and Determination of Molar Mass
Colligative Properties and Determination of Molar Mass
When a non-volatile solute is dissolved in a volatile solvent, the vapour pressure of the solvent falls (as established in the study of vapour pressure of solid-in-liquid solutions). Several measurable properties of the solution are tied directly to this drop in vapour pressure.
What makes a property "colligative"
The striking feature of these properties is that their magnitude depends only on how many solute particles are dissolved — not on what those particles are. A mole of glucose and a mole of urea, dissolved separately in the same amount of the same solvent, produce the same effect, because each contributes the same number of particles.
A colligative property depends on the number of solute particles in solution relative to the total number of particles present, and is independent of the chemical nature of the solute. The word comes from Latin — co (together) and ligare (to bind).
The four colligative properties
Four such properties are studied, all rooted in the lowering of vapour pressure:
- Relative lowering of vapour pressure of the solvent
- Elevation of boiling point of the solvent
- Depression of freezing point of the solvent
- Osmotic pressure of the solution …