Colligative Properties

Colligative Properties

Colligative properties depend only on the number - not the kind of solute particles present.

Electrolytes in Solution

1. Electrolyte is any substance containing free ions

2. Ionic compounds

a. When they dissolve they dissociate. (example: NaCl)

b. Individual Na+ and Cl- ions are created when NaCl is dissolved

3. 1 mole of NaCl makes------2 moles of ions (Na+ and Cl-)

4. 1 mole Al(NO3)3 makes----4 moles of ions (Al+3, NO3-, NO3-, NO3-)

Non Electrolytes in Solution

1. Non Electrolyte is a substance that does not dissociate into ions when in solution

2. Covalent molecules

a. When they dissolve they do not dissociate. (example: C6H12O6)

3. 1 mole of C6H12O6 makes---1 mole of hydrated C6H12O6

Electrolytes have a bigger impact on melting and freezing points per mole because they make more pieces.

Vapor Pressure

1. The bonds between molecules keep molecules from escaping.

2. In a solution, some of the solvent is busy keeping the solute dissolved.

3. Lowers the vapor pressure. (presence of solute)

4. Electrolytes form ions when dissolved - more pieces.

5. NaCl èNa+ + Cl------2 pieces: More particles greater effect

Boiling point Elevation

1. The vapor pressure determines the boiling point.

2. A non-volatile (will not vaporize or become a gas) solute lowers the vapor pressure which raises the boiling point.

a. example: Salt water boils above 100ºC

3. For every 1000 g of water, the BP increases 0.52˚C

Freezing Point Depression

1. Solids form when molecules make an orderly pattern.

2. The solute molecules break up the orderly pattern.

3. Makes the freezing point lower.

a. example: Salt water freezes below 0ºC

b. antifreeze in cars and salt on ice

4. For every 1000 g of water, the FP decreases 1.86˚C