How can homogeneous and
heterogeneous mixtures be…
1. …classified?
2. …separated?
1. HETEROGENEOUS
MIXTURE
2. COLLOID
3. EMULSION
4. SUSPENSION
5. FILTRATION
6. TYNDALL EFFECT
7. HOMOGENEOUS
MIXTURE
8. SOLUTION
9. SOLUTE
10. SOLVENT
11. MISCIBLE LIQUID
12. DISTILLATION
Cannot be decomposed into simpler
substances by chemical change
114 known elements
2 more predicted
Two or more
elements combined
with chemical bonds
Can be decomposed into
simpler substances
Chemical changes
needed
2+ substances NOT chemically combined.
Variable composition: made of more than 1 substance
Components retain their characteristic properties
Separate using physical change
Variable composition
› English: made of a variety of substances
Components retain their characteristic
properties
› English – salt is salt, water is water
May be separated into pure substances
by physical methods – see next slide
Distill
Evaporate
Let them settle/use centrifuge
Filter
Chromatography
Same throughout - texture, color, etc.
Components indistinguishable
Separate w/physical change
Example: sweetened drinks
Smallest particle size – molecular/atomic size Solute = what is dissolving (e.g. salt) Solvent = what the solute is dissolving in, which is usually a fluid- liquid or gas (e.g. water) Solvent pulls apart the molecules of the solute. Does not usually separate on its own – because the solvent holds the particles of the solute tightly (evaporation, distillation)
Water dissolves
many
substances
Ionic or polar
covalent
Solids in solids - Alloys – e.g. brass
Gases in gases – air is a homogeneous
mixture of gases
Gases in liquids – carbon dioxide in water
(carbonated drinks)
Solutions made from
liquids
Mix totally
Example: water and
rubbing alcohol
Separate via distillation
Some liquid solutions do
not contain water, e.g.
petroleum
Homogeneous mixture
Look like solutions.
A substance trapped inside another
substance.
Particles about size of bacteria (not
visible w/out microscope)
Tyndall effect.
Separated via
distillation/evaporation
For example: shaving cream, latex
paing
Boil the liquid,
forming a vapor,
then condense
vapor into liquid
again
Heat solution, the liquid evaporates the
solid left behind.
Example: separating salt from water
1.Emulsion
2.Suspension
3.Heterogeneous
Particles broken up – smaller than mud,
larger than bacteria
Need to be centrifuged
E.g. homogenized milk, mayonnaise
Solid mixed with liquid
Settles by itself (e.g. orange juice, mud in
water)
Separated via filtration
Like a snow-globe, unhomogenized milk
Particles are size of fine mud particles
Incompatible substances (no dissolving)
Separate easily on their own (e.g. by density)
Gravitational pull only (settling).
Examples: Water and Oil, oil and salt
Centrifuge, natural settling
Assignment
Solution Heterogeneous mixture Colloid
Define Two or more substances
which do not dissolve. Repel
each other.
Example Lava lamp, oil and vinegar,
coffee (before you filter it)
How are they
separated?
Filtration
How is it similar
to…
A heterogeneous
mixture?
A colloid?
A solution?
don’t dissolve; big particles
Your assignment
1. Why is water called the universal
solvent?
2. How do substances dissolve?
3. How do solutes affect a solution?
1. Polar compound
2. Nonpolar
compound
3. Hydrogen bond
Uneven distribution of charge
› Ionic compounds – polar
› Some molecular (covalent) compounds too
Water – polar covalent compound
Water dissolves polar compounds
because water molecules attract both
positive and negative ions
Polar water molecules pull ionic crystals apart, as shown below.
• The partially negative oxygen atoms of water molecules attract the
positively charged sodium ions.
• The partially positive hydrogen atoms of water molecules attract the
negatively charged chloride ions.
Dissolving depends on the forces between particles. › The forces between the solvent molecules and the
particles of the substances must be greater than the force between the particles in the crystal.
Water dissolves many NONPOLAR compounds. › Water forms hydrogen bonds with NONPOLAR
molecular compounds such as sugar.
hydrogen bond: the intermolecular force occurring when a hydrogen atom that is bonded to a highly electronegative atom of one molecule is attracted to two unshared electrons of another molecule
Like dissolves like. › A solvent will dissolve substances that have
molecular structures that are like the solvent’s structure.
Nonpolar compounds usually will not dissolve in water. › nonpolar: describes a molecule in which the
centers of positive and negative charge are not separated
› Nonpolar solvents are used to dissolve nonpolar materials.
〉 Why do substances dissolve?
〉 The energy transferred from the solvent
to the solute, as well as the attractive
forces between the solvent and solute
molecules, causes molecules at the
surface of the crystal to dissolve.
Solutes with a larger surface area dissolve faster. › More solute particles are exposed to the solvent.
Stirring or shaking a solution helps the solute dissolve faster. › Dissolved solute particles diffuse throughout the
solution faster. › More solute particles can dissolve.
Solutes dissolve faster when the solvent is hot. › Collisions occur between solute and solvent
particles more frequently and with more energy.
Solutes affect the physical properties of a solution. › Solutes increase the boiling point of a solution.
If you dissolve salt in water, it will boil at a higher temperature.
› Solutes lower the freezing point of a solution. The coolant mixture of ethylene glycol and
water keeps a car’s radiator fluid from freezing in winter.
Polar-polar
› Water-salt
› Ethanol-ink
Nonpolar-nonpolar
› Oil paint + nonpolar solvent
Surface area
Stirring/shaking
Heat
Solutes affect the physical properties of a solution. › Solutes increase the boiling point of a solution.
If you dissolve salt in water, it will boil at a higher temperature.
› Solutes lower the freezing point of a solution. The coolant mixture of ethylene glycol and
water keeps a car’s radiator fluid from freezing in winter.
1. What is solubility?
2. How do saturated solutions react when
more solute is added?
3. What is concentration, and how can it
be calculated?
Solubility
Concentration
Saturated solution
Unsaturated solution
Supersaturated solution
Molarity
〉 What is solubility?
〉 The solubility of a substance is the maximum mass of a solute that can dissolve in 100 g of solvent at a certain temperature and standard atmospheric pressure.
solubility: the ability of one substance to dissolve in another at a given temperature and pressure
Different
substances have
different
solubilities.
How much of substance is in a solution?
To express how much of a substance can dissolve in a solvent, you need to use the concentration.
Concentration: the amount of a particular substance in a given volume of a mixture, solution, or ore › A concentrated solution has a large amount of
solute.
› A dilute solution has only a small amount of solute.
〉 What happens when you add more solute to a saturated solution?
〉 In a saturated solution, the dissolved solute is in equilibrium with undissolved solute. So, if you add more solute, it just settles to the bottom of the container.
saturated solution: a solution that cannot dissolve any more solute under the given conditions
Unsaturated solutions can become saturated.
unsaturated solution: a solution that contains less solute than a saturated solution does and that is able to dissolve additional solute
Heating a saturated solution can dissolve more solid. › The solubility of most solutes increases with
temperature.
supersaturated solution: a solution that holds more dissolved solute than is required to reach equilibrium at a given temperature. › To make a supersaturated solution, you
raise the temperature of a solution, dissolve more solute, then let the solution cool again.
Temperature and pressure affect the solubility of gases.
Gaseous solutes are less soluble in warmer water. • Example: Soda goes flat quickly at room temperature.
Gases are more soluble under higher pressure. • Example: When a can of soda is opened, carbon dioxide gas
that had been dissolved in the soda bubbles out of solution.
〉 How do you describe how much of a solute is in a solution?
One of the most common ways of expressing the concentration of solution is molarity.
Molarity: a concentration unit of a solution expressed in
moles of solute dissolved per liter of solution.
mol
= , or M L
moles of solutemolarity
liters of solution
Concentration = mass ÷ molar mass ÷
volume
M = Grams ÷ g/mol ÷ Liters
OR M = mol ÷ liters
Example:
What is the concentration of a solution
which contains 36 moles of magnesium
carbonate in 0.1 liters?
36 moles ÷ 0.1 liters = 360 M
Moles = Concentration x volume
mol = M x L
Example:
How many moles of hydrochloric acid are
in 0.300 liters of a 2 M solution?
Moles = 2M x 0.300 liters = 0.6 moles
Mass = Concentration x volume x molar
mass
g = M x L x g/mol
Example:
How many grams of
Copper (II) sulfate· 5H2O are required to
make 0.200 L of a 1M solution? The molar
mass of Copper (II) sulfate · 5H2O is
249.72 g/mol.
1. Calculating Molarity 1. M = mol ÷ L
2. M = g ÷ g/mol ÷ L
2. Calculating Volume 1. L = M x mol
2. L = g x g/mol
3. Calculating Moles 1. mol = M x L
4. Calculating Mass 1. g = M x L x g/mol