1. Properties of Solutions

2. Boiling-Point Elevation and Freezing-Point Depression

3. Colligative Properties
Properties that are ONLY dependent on the number of solute particles
Not dependent on their identity
Examples
Boiling-point elevation
Freezing-point depression
Osmotic pressure

4. Boiling-Point Elevation
Nonvolatile solutes elevate the boiling-point of the solvent
ΔT= Kbmsolute
ΔT - boiling point elevation
Kb - the molal boiling point elevation constant of the solvent
msolute – the molality of the solute in the solutions

5. Freezing-Point Depression
Solutes depress the freezing point of the solvent
ΔT= Kfmsolute
ΔT - freezing point depression
Kf - the molal freezing point depression constant of the solvent
msolute – the molality of the solute in the solutions

6. Osmotic Pressure
Osmosis – flow of solvent molecules into a solution through a semi-permeable membrane
Small concentration of solute produces a relatively large osmotic pressure

8. Osmotic Pressure
The pressure necessary to keep water from flowing across a semi-permeable
Osmotic pressure can be used to characterize solutions and determine molar masses
π = MRT
π – osmotic pressure in atmospheres
M – molarity of the solution
R – gas law constant
T – Kelvin temperature

9. Osmosis
Dialysis – transfer of solvent molecules as well as small solute molecules and ions
Isotonic Solutions – solutions that have the same osmotic pressure
Osmotic Pressure in Living Cells
Crenation – cells placed in a hypertonic solution lose water to the solution and shrink
Hemolysis – cells placed in a hypotonic solution gain water from the solution and swell, possibly bursting

10. Reverse Osmosis
External pressure applied to a solution can cause water to leave the solution
Concentrates impurities (salt) in the remaining solution
Pure solvent (water) is recovered on the other side of the semi-permeable layer

11. Colligative Properties of Electrolyte (Ionic) Solutions

12. van’t Hoff Factor (i)
van’t Hoff Factor (i) – the relationship between the moles of solute dissolved and the moles of particles in solution i = moles of particle in soln moles of solute dissolved
For ionic compounds, the expected value of i is an integer greater than 1
NaCl – 2, BaCl2 – 3, etc.

13. van’t Hoff Factor (i)
Values of i are less than expected due to ion pairing
Ion pairing – phenomenon occurring in solution when oppositely charged ions aggregate and behave as a single particle
Closer to expected values in more dilute solutions

14. van’t Hoff Factor (i) Incorporating the van’t Hoff
Boiling point/freezing point
ΔT = imK
Osmotic Pressure
π = iMRT

15. Colloids Colloid – suspension of particles in some medium
Particles do no precipitate out because of electrostatic repulsion
Tyndall effect – the scattering of light by particles and is used to distinguish between a suspension and a true solution
Light passes through a solution
Light is scattered in a colloid