Solutions
Pure Substances & Mixtures
Everything! (har har)
o What's the matter?
o Pure Substances have a definite set of physical properties.
o (melting point, density, reactivity, etc)
o Elements – cannot be broken down
o Compounds – can be broken down
o Mixtures are two or more substances physically combined
but not chemically combined
o Heterogeneous- a mixture that is not uniform throughout.
o Looks opaque – particles are large enough to block light
o Examples: dirt, chocolate chip cookies, milk, you
o Homogeneous- uniform throughout
o Solution- a special homogeneous mixture where one substance is
dissolved into another. Almost always clear.
o Examples: salt water (ionic compound + water), syrup, rubbing
alcohol
Mixtures
Activity:
•
•
1. Left-hand side of your notebook, draw 4 gas tanks and label them “H2 Gas,” “O2 Gas,”
“Hydrogen & Oxgen compound,” and “H2 & O2 Mixture.”
2. Fill each tank with the appropriate molecules. Use open circles for hydrogen atoms and
filled-in circles for oxygen atoms.
H2 Gas
Pure
O2 Gas
Pure
Oyxgen &
Hydrogen
Compound
Pure
O2 & H2
Mixture
Not pure
Not pure
Separating Mixtures
 Separating Mixtures:
 distillation – using different boiling points to separate substances
in a mixture
 Examples: desalination
 filtration – Using particle size to separate substances through a
semi-permeable membrane.
 Examples: air filter in a car, tea bag, coffee filter
 Chromatography- using a molecule’s ability to move through a
medium. (demo)
 Examples: gel electrophoresis, HPLC
Solutions
• Solutions have two components:
• Solvent – major component of a solution, dissolves the solute
• Solute – minor component of a solution,dissolved by solvent
• The solute is the active ingredient of a solution.
• Solutions used in chemical equations have (aq) added
• aq = aqueous
• Steps of solution process: Known as solvation. (video)
• Solute particles separate – energy is absorbed in order to
separate solute particles
• Solvent molecules separate – energy also absorbed
• Solvent particles surround solute particles – energy is released
• Solutions that release more energy than absorbed are called
exothermic (energy EXiting).
• Solutions that absorb more energy than released are called
endothermic (energy ENters)
Solubility
 Solubility- able to be dissolved
 Solids, liquids and gases can be dissolved.
 “Like dissolves Like”
Ionic & polar solutes dissolve in polar solvents.
Non-polar solutes dissolve more in non-polar solvents.
•
Immiscible - liquids that are not soluble in each other
●
Ex: Oil and water do not dissolve in each other because of
different polarities: Water is polar and oil is nonpolar
• Solubility
 Not all ionic compounds are soluble in water
 Insoluble compounds will fall out of solution, forming a
precipitate
 Solubility for ionic compounds can be predicted using
solubility rules
Temperature & Pressure
Temperature and solubility
• Solids dissolve better at higher temperatures
• Faster solvent particles allow solute particles more movement
• Example: hot tea can dissolve more sugar than cold tea
• Gases do not dissolve well at higher temperatures
• Gas molecules tend to disperse with higher temperatures
• Example: soda bottle at room temperature will be less fizzy
than when cold
Pressure and solubility
• Pressure has no effect on solid solutes
• High pressure allows gases to dissolve better
• High pressure does not allow gas molecules to disperse easily
• Example: sealed soda bottles stay fizzy longer
Saturation
 Saturated solution- solution containing the maximum amount of
solute for a specific amount of solvent at a given temperature and
pressure.
 More solute will not dissolve
 Unsaturated solution- does not contain the maximum amount of
solute in solution.
 More solute can dissolve until the maximum is reached
 Supersaturated solution- an unstable solution that contains more
solute than it can theoretically hold at a given temperature
 Created by cooling a saturated solution
 Adding more solute causes the excess solute to precipitate
•
Precipitate- a solid that forms and settles down in a liquid mixture
Solubility Curves
• Solubility Curve– graph of solubility versus
temperature
• compares the solubilities of multiple compounds in
water as a function of temperature.
• solubility is expressed in terms of grams of solute
per 100 grams of H2O.
Solubility
Curves
 How many grams
of KNO3 can
dissolve in 100
grams of water at
30ºC?
 Answer: About
48 grams.
Solubility
Curves
 How many grams
of KClO3 can
dissolve in 100
grams of water at
55ºC?
 Answer: About
25 grams.
Solubility
Curves
 How many
grams of NH4Cl
can be
dissolved in
200 grams of
water at 40ºC?
 Answer: About
96 grams.
Solubility
Curves
 A saturated
solution of NaNO3
is prepared at
70ºC in 100
grams of water. If
the temperature is
lowered to 40ºC,
how many grams
of NaNO3 will
precipitate?
 Answer: About
30 grams will
precipitate out.
Solubility
Curves
 If 35 grams of
NH4Cl are
dissolved in 100
grams of water at
30ºC, is the
solution
unsaturated,
saturated, or
supersaturated?
 Answer: The
solution is
unsaturated.