Solutions

Chapter 8, Section 1 - Solutions and Other Mixtures                                                                                                                                                     


Mixture - A combination of two or more substances that are not chemically combined.

Heterogeneous Mixture - A mixture in which the components are not evenly spread throughout the mixture.
  • In some heterogeneous mixtures (like a chocolate chip cookie), you can see the different components.
  • There is not a fixed composition (one part may have different material or different proportions of materials than another).
    • Like the cookie: one part may have a chocolate chip, another part might not.
  • Suspension - A mixture in which particles will settle out over time. (ex. - orange juice with pulp)
    • Can be filtered (particles are 1,000 nm or larger)
    • Can be two liquids (ex. - oil and water)
  • Colloid - A heterogeneous mixture in which particles do not settle out over time.  (ex. - jello, egg whites, milk, fog, smoke, whipped cream)
    • Particles are too small to filter out (1 to 1,000 nm).
    • Colloids show the Tyndall Effect - When a beam of light is shone through a colloid, you can see the beam.
      • You can't see the beam in a true solution.

Miscible - When two substances are able to mix.  (They form one layer.)
Immiscible - When two substances do not mix.  (They form two separate layers.)

  • Emulsion - A colloid in which two immiscible liquids are spread throughout each other.  (Two unmixable liquids are mixed!)
    • ex. - Mayonnaise - The oil and vinegar are prevented from separating by the egg yolk, which coats the oil droplets and stops them from forming a separate layer.
Homogeneous Mixture - A mixture which looks the same all the way through (even under a microscope).
  • Solution - A homogeneous mixture in which the molecules of two or more substances are evenly dispersed.  (ex. - Kool-Aid)
    • Solute - The substance that gets dissolved in the solvent.  (ex. - Kool-Aid powder)
    • Solvent - The substance that dissolves the solute.  (ex. - Water)
  • When solute dissolves, it separates into individual atoms/molecules/ions.

  • Types of solutions...
    • Gas & Gas   (air)
    • Gas & Liquid   (soda)
    • Liquid & Liquid    (water & food coloring)
    • Liquid & Solid    (saltwater)
    • Solid & Solid    (bronze)
      • Alloy - A solid or liquid mixture of metals.

Homework
    Pg. 266 #1-7


Chapter 8, Section 2 - How Substances Dissolve                                                                                                                                                         

Water is called the "Universal Solvent" because so many things can dissolve in it.
It is not truly universal, because some things don't dissolve in water.

Water can dissolve ionic compounds because it is a polar molecule.  (It has partial charges on each end.)
Water molecules attract ions and surround them.
Only works if enough H2O surrounds each ion to overcome the ionic bonds.
(The attraction of the H2O's must be stronger than the attraction of the ions for each other.)
((If not, the ionic compound won't dissolve!))

Rule: For an ionic substance to dissolve...
...the force between solvent molecules and solute molecules/ions must be stronger
  than the force between solute molecules/ions.

Water surrounds and separates polar molecules.

Rule: Like dissolves like.
Polar solvents dissolve polar solutes.
Nonpolar solvents dissolve nonpolar solutes.

The Dissolving Process
Particles in liquids tend to move faster than particles in solids => the solvent particles have more energy.
As solvent particles collide with solute particles, they transfer some energy to the solute.
If enough energy is transferred, solute particles on the surface leave the crystal and dissolve.

Dissolving goes faster when...
- you heat it up.  (particles move faster, give more energy)
- you shake/stir it.  (particles move faster, spread out more)
- you crush it up.  (more surface area for solvent to act on)

Solute changes the properties of a solution.
Lowers freezing point.  (Ocean doesn't freeze in winter.)
Raises boiling point.  (Add salt to water when cooking pasta!)


Homework:
    Pg. 273 #1-6

Chapter 8, Section 3 - Solubility and Concentration                                                                                                                                                      

Solubility - The ability of one substance to dissolve in another (at a given temperature and pressure).
  • The mass of solute that can dissolve in 100g of water at a given temperature and at standard atmospheric pressure.
    • ex. - 36g of NaCl dissolve in 100g of water at room temperature.
    • Different substances have different levels of solubility.
  • Soluble - Able to be dissolved.  (Salt in water.)
  • Insoluble - Not able to be dissolved.  (Oil in water.)

Concentration - The amount of solute dissolved in a certain amount of solution.
  • Concentrated - Has a lot of solute.
  • Dilute - Has a little solute.

Saturated Solution - A solution that cannot dissolve any more solute (under the current conditions).
Unsaturated Solution - A solution that can still dissolve more solute.  (It is not full yet!)

Supersaturated Solution - A solution that contains more solute than it normally would.
Start by heating up a saturated solution => this allows it to dissolve more solute.
Once the heated solution is saturated, cool it down.
The extra solute will not come out of solution unless it has a surface to crystallize on.

Gases are...
...less soluble as temperature increases.
...more soluble as pressure increases.

Molarity (M) - A measure of concentration of a solution.  Molarity (M) is the number of moles in 1 L of solution.
1.0 M NaCl  ("one molar solution of NaCl") contains 1 mole of salt for every liter of water.