1. Solvation, Solubility, and Colligative Properties
Solutions
Solvation, Solubility, and Colligative Properties

2. Pure Substances vs. Mixtures
Pure Substances- can’t be broken down without a chemical reaction
Elements and Compounds
Mixtures- can be separated
Heterogeneous- not the same throughout
Suspensions- particles settle
Colloids- particles make “beam” (Tyndall effect)
Homogeneous- the same throughout
Solutions

3. Solutions Solutions made up of… Solute- the thing that is dissolved
Solvent- the substance that the solute is dissolved in
Ex: When making Kool-Aid, the powder is the SOLUTE and the water is the SOLVENT

4. What is happening when something dissolves?
Polar Solvent & Polar (Ionic) Solute:
Polar ends attract the ions in the solid and pull them away from the crystal
They become SOLVATED – surrounded by solvent molecules
If attractions between the ions in the solute are stronger than the attractions from the solvent, it is INSOLUBLE

5. Nonpolar Solvent & Nonpolar solute
Covalent compounds do not break up in solutions like ionic ones do
Nonpolar- no attractive OR repulsive forces
Don’t really “dissolve”, they mix because of entropy

6. Solubility Curves
Show the amount of a solute (g) that can be dissolved in a certain amount of solvent (usually 100 g of H2O) at a certain temperature
Unsaturated solution- can dissolve more solute (under line)
Saturated solution- cannot hold any more solute at that temperature (on line)
Supersaturated- holds more solute than normal for that temperature (above line)
Must be heated and cooled quickly. One seed crystal can cause crystallization (rock candy)

7. Practice Problem
How many grams of KNO3 should be added to 250g of water at 40°C to make a saturated solution?

8. Colligative Properties
Colligative properties are dependent on the number of particles in a solution
Vapor Pressure Reduction/ Boiling Point Elevation
Freezing Point Depression

9. Vapor Pressure Reduction and Boiling Point Elevation
Vapor Pressure- pressure exerted by vapor of the liquid in a closed system
If a solute is added, the vapor pressure is LOWERED
Dissolved particles at the liquid surface, so less surface area for the solvent particles to escape
Results in less solvent in air
Boiling Point Elevation: Because adding a solute lowers vapor pressure, it takes more energy to vaporize the particles.

10. Boiling Point Elevation

11. Freezing Point Depression
Freezing Point Depression: Adding solute causes the freezing point to be LOWER
Freezing requires particles to form a crystal
Solute molecules “get in the way” and prevent the molecules from freezing (and melting)

12. Freezing Point Depression

13. Changing Colligative Properties
Colligative properties are changed by adding solute
Change is proportional to the number of particles the solute makes
NaCl would decrease by twice as much as glucose (C6H12O6) would
glucose= covalent, NaCl= ionic
Only ionic compounds break up in solution.
MgCl2 (3 particles) would decrease it more than NaCl (2 particles)