# Lecture 22: Boiling/Freezing Points and Colligative Properties

• Elevation of boiling point ﻿$\rightarrow$﻿ Depends on the number of moles and properties of solvent

#### depression of freezing point

• ﻿$T = Kb * m$﻿ (﻿$m$﻿ - molarity of the solution)
• So ﻿$T = Kb$﻿ when ﻿$m = 1$﻿ so ﻿$Kb$﻿ is defined as the elevation of boiling point of a unimodal solution
• Colligative Properties ﻿$\rightarrow$﻿ Only on properties
• Depends only on the number of molecules and not chemical nature
• Osmosis - Solvent passes through membrane
• Dialysis - Solute passes through membrane
1. Calculate molarity of solution
2. Number of particles
• Ion Pairing ﻿$\rightarrow$﻿ Explains why ﻿$i$﻿ measured is lower than ﻿$i$﻿ expected - the number of particles
• Ions pair and then share particles