Solutions
Chapter 8
Mixtures
• Mixtures = always composed of two or more pure substances
that do not combine chemically
• The ratio of the components of the mixture are not fixed
• The properties of a mixture are always mid-way between
those of its components
Mixtures, cont’d
• Can be homogeneous or heterogeneous
• Homogeneous: the mixture is the same no matter where you
look
• Another name for a homogenous mixture is solution.
• Heterogeneous: the mixture is different in different areas
Separating Mixtures
• Filtration = separates a solid
and a liquid
• Solid gets trapped by the filter and
the liquid passes through
• Solid is called the precipitate
Separating Mixtures, cont’d
• Separatory funnel = can separate two
liquids that do not combine
Separating Mixtures, cont’d
• Paper chromatography
separated components of a
mixture based on size
• Small molecules travel farther
up the paper than bigger
molecules
• Produces different colors
Separating Mixtures, cont’d
• Distillation uses the different boiling points of the mixture
components to separate them
• Component with the lower boiling point boils first and is collected
• Component with the higher boiling point stays in the original
container
The Process of Distillation
After Distillation
Solutions Vocabulary
• Solute: the substance being dissolved
• Solvent: the substance doing the dissolving
• Aqueous: a solution with water as the solvent
• NaCl(aq) = sodium chloride dissolved in water
Properties of Solutions
• Solutions are always homogenous mixtures
• Solutions are always clear, but may be colored
• Solutions never settle upon standing
• Solutions pass through a filter
Solubility and Polarity
• Solubility: a measure of how well a solute dissolves in a
substance
• “Like dissolves like” = polar solutes dissolve in polar solvents
and nonpolar solutes dissolve in nonpolar solvents
• Water = polar
• Can dissolve polar and ionic solutes (salts, sugar, etc)
• Cannot dissolve oil, which is nonpolar
Solubility and Polarity, cont’d
• When an ionic solute dissolves
in water, it gets pulled apart into
individual ions
• It dissociates
• Each ion is surrounded by water
molecules
• These solutions conduct
electricity—they are electrolytes
Solubility and Polarity, cont’d
• When a molecular solute
(like sugar) dissolves in
water, its individual crystals
are not pulled apart
• It does not dissociate
• These solutions do not
conduct electricity—they are
nonelectrolytes
Solubility and Polarity, cont’d
• Soap is both a polar and
nonpolar molecule
• One end is polar and can
dissolve in water
• The other end is nonpolar and
can dissolve grease and oils
Solubility and Temperature
• Solids and liquids dissolve best at high temperatures
• Particles move faster, speeding up dissolving
• Gases dissolve best at low temperatures
• Particles move slower, so the gas cannot escape
Solubility and Pressure
• Solids and liquids are not greatly affected by pressure
• Almost no effect at all, so pressure can be ignored
• Gases dissolve best under high pressure
• Forces the gas to stay in the liquid instead of escaping
Solubility Guidelines—Table F
Solubility Curves—Table G
• There are three types of solutions:
Solution
Saturated
Unsaturated
Supersaturated
Definition
What Happens if You Add More Solute?
The solution is holding as much Added solute sinks to the bottom
solute as it can
The solution has room for
Added solute dissolves
more solute
The solution is holding more
solute than it could normally
Added solute makes all the extra solute sink
to the bottom
Solubility Curves—Table G
• A solubility graph shows how much of a specific solute can
dissolve in a solvent at a specific temperature
• Solvent is 100 grams of water
• Temperature ranges from 0°C to 100°C
supersaturated
saturated
unsaturated
Solubility Curves—Table G
• If the amount of grams of water changes, the amount of
grams of solute changes too
• Ex: At 90°C, a saturated solution of NaCl contains 40 g of
solute in 100 g of water
• If the water doubles to 200 g, the amount of NaCl also doubles to 80 g
• If the water halves to 50 g, the amount of NaCl also halves to 20 g
Molarity
moles
Molarity =
liters
Parts per Million
ppm =
Grams of solute × 1,000,000
Grams of solution
Colligative Properties
• Colligative properties = change depending on the amount of
solute dissolved in the solvent
• Ex: freezing point and boiling point
• More solute = lower freezing point
• More solute = higher boiling point
• Ex: saltwater freezes at a lower temperature than pure water,
but boils at a higher temperature
Colligative Properties, cont’d
• Salt is put on icy roads to cause the water to freeze at a lower
temperature
• Stays liquid at colder temperatures
• More ions in solution = lower freezing point and higher
boiling point
NaCl (ionic)
NaCl  Na+ + Cl-
NH3 (molecular)
NH3 (s)  NH3 (aq)
CaCl2 (ionic)
CaCl2  Ca2+ + 2 Cl-
Ca2+
Na+
NH3
ClCl-
Cl-
2 moles
1 mole
3 moles
Vapor Pressure
• The pressure a gas exerts on the top of a liquid
• Table H shows how changing the vapor pressure affects the
liquid’s boiling point
• 101.3 kPa = normal boiling point
• The higher the boiling point, the stronger the intermolecular
forces