Solutions
But first, a look at the big picture…
 Pick
out any object in the room, and
it can be one of two things:
a pure substance or a mixture
(Almost everything you pick will be a
mixture.)
But first, a look at the big picture…
Elements are pure substances…
Elements are substances that are composed of only one kind of atom.
Elements cannot be broken down by chemical change.
Practice question:
 Which
of these could not be
decomposed in a chemical reaction?
A. Sodium
B. Carbon dioxide
C. Carbon
D. Sodium chloride
Compounds are also pure substances…
A compound is a pure substance made of different elements,
chemically bonded together. ALWAYS in the same proportions.
Mixtures are not pure substances; their composition can vary.
In each example above, there’s more than one thing there!
Mixtures of hydrogen and oxygen
could be 1% oxygen, 5%
oxygen,18% oxygen or 64% oxygen.
But in a compound (like water), the
% oxygen is always the same.
Old TAKS question:
 Which
of these are composed of two
or more different substances that are
chemically combined in a definite
ratio?
F Compounds
G Mixtures
H Elements
J Solutions
Another TAKS question:
What characteristic of water remains
the same no matter what is dissolved
in it?
A The ratio of hydrogen to oxygen
B The ability to refract light
C The hydroxide ion concentration
D The freezing temperature
Check your understanding:
How many of these are mixtures?
(And which ones are they?)
Another practice:
Given the diagrams X, Y, and Z below:
Which diagram or diagrams represent a mixture of elements A and B?
Identify each as an element, compound, or mixture.
Back to the big picture…
Note: A pure substance can be represented by a chemical formula.
Examples: Fe, H2, NaCl, CO2
Give four more examples in your notes.
Mixtures
Heterogeneous Mixture
 Mixture
that does not have the same
properties throughout the mixture
 Individual substances remain distinct
 Can you think of another example of
a mixture that would be
heterogeneous?
A solution is a homogeneous
mixture: has the same properties
throughout
“homo” = the same
Solutions occur in all phases



Solid solution: steel
Gas solution: air
Liquid solutions: most common in chemistry
Alloys
 An
alloy is a solution where two or
more solids are combined.
• A homogeneous mixture of metals
Why use alloys instead of pure metals?
• Can increase strength and durability
by combining properties of different
metals
Now Practice!
Are these examples of elements,
compounds, homogeneous mixtures, or
heterogeneous mixtures?
1. Air
2. Bronze
3. Calcium
4. Raisin Bran
5. Orange juice (with pulp)
6. Salt water
Solution Vocabulary



The solvent does the dissolving: whatever you
have more of.
The solute is dissolved; it’s the thing you have
less of.
Memory trick: “solvent” has more letters than
“solute,” so it’s the thing you have more of.
Recap: Solutions
•Solution:
homogenous mixture
~ Mixture: parts are not chemically combined
~ each component of the solution keeps its
identity
~ won’t settle out
composed of solute and solvent
gets
dissolved
does the dissolving
Solutions
• name the solute/solvent in the following
solutions…
solvent
solute
salt water
salt
atmosphere
other gases
N2
Zn
Cu
brass
(Zn and Cu)
water
Why does anything even
dissolve? Why doesn’t it
just sit there?
Why does anything even dissolve? Why
doesn’t it just sit there?
Solubility guideline:
“Like dissolves like.”
Polar solvents (like water) dissolve polar
things.
Non-polar solvents (like oil) dissolve nonpolar things.
Polar? Non-polar?
Something is polar if it has two
opposite ends.
The earth is polar because it
has a north pole and a south
pole.
A person is bi-polar if they
have two opposite moods.
Polar? Non-polar?
In
chemistry, a molecule is polar
if it has one end with a + charge
and one end with a – charge.
Polar? Non-polar?
What determines whether a
molecule is polar?
Remember electronegativity?
Electronegativity is the ability
of an atom to attract shared
electrons towards itself.
 When
atoms share electrons in a
covalent bond, they have a tug of
war over the electrons.
If the two atoms have different electronegativities,
they won’t share the electrons evenly. One atom will
pull harder on the electrons than the other atom.
Oxygen has a higher electronegativity than hydrogen,
so oxygen wins the electron tug-of-war. The electrons
spend more time on the oxygen end of the molecule.
Be sure to know that water is a polar
molecule because the oxygen atom
does not share the electrons equally
with the hydrogen atoms.
Therefore, a water molecule has a
partially negative end and a partially
positive end.
It’s the polarity of water that
makes it such a good solvent:
Let’s see how it works:
http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/molvie1.swf
A little more vocabulary…
Saturated solution: a solution that is holding all the
solute it can hold at a given temperature
(Think of a saturated sponge: it can’t take any more!)
 Unsaturated solution: a solution containing less than
the maximum it can hold
(Like a dry sponge: it can still hold more)

Solubility
 Solubility:
the amount of a solute
that will dissolve in a given solvent
 What
factors affect solubility?
Temperature Effects
 Higher
temperature usually increases
the solubility of a solid in a liquid.
But not always!
 We must read the effect of
temperature from a graph of
experimental data.
• Which substance is most soluble at 40°C?
NaNO3
• How many grams of NH4Cl will dissolve at 50°C? ~ 50 grams
•What two substances have the same solubility at 24°C? KNO3 and
Yb2(SO4)3
• How many grams of NaNO3 will dissolve in 300.0g of water at
(80 x 3)
10.0°C? ~ 240 grams
A future test question:
 How
does soap work?
If your mother cooks bacon, and asks you to clean
the pan, will the pan get clean if you just rinse it off?
Soap
CH2
CH3
CH2
CH2
OP
CH2
CH2
CH2
CH2
O-
O-
Soap
CH2
CH3
CH2
 Soap
has a long
non-polar end
P
CH2
CH2
CH2
O-
CH2
CH2
O-
O-
Soap
CH2
CH3
CH2
CH2
OP
CH2
CH2
CH2
CH2
 And
end
O-
O-
a polar
O-
CH2
CH3
CH2
CH2
P
CH2
CH2
CH2
CH2
_
O-
O-
A
drop of bacon grease in water
 Grease is non-polar
 Water is polar
 Soap lets you dissolve the non-polar
in the polar.
Non-polar ends
dissolve in
grease
Polar ends
dissolve in water
 Soap
molecules tie the grease to the
water, so when you rinse away the
water, the grease goes along with it!.
Factors that affect the rate of
dissolving:
1.
2.
3.
Temperature (solutes dissolve
faster in hotter solvents) Why?
Surface area (sugar granules
dissolve faster than a sugar cube of
equal mass)
Stirring (brings fresh, unsaturated
solvent in contact with the solute)
Dissolving Gases
 If
you’re trying to dissolve a gas in a
liquid, 2 factors affect solubility:
• Temperature of the solvent (less gas
will dissolve in a warmer solvent)
• Pressure (increasing the pressure will
increase the amount of gas you can
dissolve)
Practical Applications:
gas solubility – temperature
relationship can be remembered if
you think about what happens to a
soft drink as it stands around for
awhile at room temperature. It gets
flat since more of the carbon dioxide
bubbles have escaped.
 This
Practice Question:
 Thermal
pollution is merely heat that
has been transferred to water or air.
You may think that heat is not really
pollution. But how is the
concentration of dissolved oxygen in
water affected by thermal pollution?