1. Mixtures and dissolving
General Chemistry Unit 10

2. Types of Mixtures
Solution: homogeneous mixture of two or more substances in a single phase
Two parts: solvent (greater amt) and solute
Does not separate on standing
Cannot be separated by filtration
Many types of solutions (p. 81)

3. Types of mixures
Suspension: heterogeneous mixture that must be stirred to keep mixed
Particles settle out
Particles over 1000 nm
Can be separated by filtration
Not transparent

4. Types of mixtures
Colloid: heterogeneous mixture with particles of intermediate size
Two parts: continuous and dispersed phases
Particles do not settle out
Particles between nm
Can be separated by a semipermeable membrane but not normal filtration

5. Classes of colloids Sol: solid in liquid (paint, mud)
Gel: solid network in liquid (gelatin, pearls, opals)
Emulsion: liquid in liquid or solid (milk, mayonnaise, cheese)
Foam: gas in liquid or solid (whipped cream, marshmallow)
Aerosol: liquid or solid in gas (fog, smoke, cloud, anything in spray can)

6. Tyndall effect Scattering of light by colloid particles
Colloids/Sunset Demo (Journal)

7. The Solution Process Factors Affecting Rate of Dissolving:
Crushing or breaking up: increases the surface area exposed to the solvent
Stirring or agitating the solution: brings fresh solvent into contact with the solute particles
Heating: faster motion gives more collisions with more energy which helps separate particles from each other and disperse them in the solvent

8. Solubility
There is a limit to how much solute can be dissolved in a certain amount of solvent.
This limit is expressed as solubility (g/100 ml solvent).
Solution equilibrium occurs when the rates of dissolving and crystallization are equal

9. Solution conditions
Saturated solution: contains the maximum amount of dissolved solute.
Unsaturated solution: contains less than the maximum amount of dissolved solute.
Supersaturated solution: contains more solute than a saturated solution under the same conditions. (Created from a saturated solution at a higher temperature that cools without forming crystals.)

10. Solution test
A solution at room temperature has no crystals in it. How can we know if it is saturated, unsaturated, or supersaturated?
TEST: Add more solute and observe the results.
Crystal dissolves: unsaturated
Crystal drops to bottom and remains unchanged: saturated
Crystal drops to bottom and grows substantially: supersaturated

11. Dissolving ionic compounds in water
Dissolving in Water
Hydration occurs between water and ionic solutes.
The water molecules are attracted to the ions and draw them away from the surface of the crystal.
The ions are surrounded by water molecules.
New ions are exposed and the process repeats, resulting in the dissolving of the entire crystal.

12. Solute-solvent interactions
Like Dissolves Like
Polar solvents dissolve polar (or ionic) solutes.
Nonpolar solvents dissolve nonpolar solutes.
Liquid solutes and solvents that are not soluble in each other are immiscible.
Liquids that dissolve in each other are miscible.

13. Dissolving effects Pressure Only affects gas solubility
Henry’s Law: the solubility of a gas is directly proportional to the partial pressure of the gas on the liquid’s surface.
Examples of Henry’s Law:
Carbonated beverages (bottled under pressure)
The “Bends” experienced by divers (more gases dissolve in blood, when rising come out as bubbles and go to brain)

14. Dissolving effects Heats of Solution
Energy change (heat absorbed or released) when dissolving takes place
Solid in liquid:
Usually endothermic, positive value, requires energy
Sometimes exothermic, negative value, gives off energy
Most become more soluble if temperature is raised
Gas in liquid:
Exothermic
Becomes more soluble at lower temperatures – fish die in
warm water (not enough oxygen)