Chapter 9 Acids, Bases, and
Solutions
P180
Solution: A mixture of 2 or more
substances that is uniform at the
molecular level.
Uniform means there are no clumps
bigger than a molecule and the
solution has the same ingredients
everywhere.
Soda is a solution. All the particles
in the soda, from the flavor
molecules to the color molecules are
evenly dispersed throughout the
bottle.
Solutions can exist in every phase:
solid, liquid, or gas.
Alloy – a solution of 2 or more solids
Steel is an alloy solution of iron and
carbon.
14-Karat gold is an alloy of silver and
gold. 14-Karat means that 14 out of
every 24 molecules in the alloy are
gold; the rest are silver.
Muddy water is not a solution.
Particles of soil are small, but still
contain thousands of atoms and
molecules clumped together.
A true solution does not have
molecules that clump together.
P181
Solution contains 2 components:
Solvent: the component of a
solution that is present in the
greatest amount.
The solvent in soda is water.
Solute: any other component of a
solution other than the solvent.
Solutes in soda are sugar, food
coloring, flavoring chemicals, and
carbon dioxide.
Dissolve: to separate and disperse a
solid into individual molecules or
ions in the presence of a solvent
Sugar water :
Solute – sugar
Solvent – water
Solution – sugar is dissolved in the
water; stirred until clear again.
The dissolving of a solid, like sugar,
occurs when molecules of solvent
interact with and separate
molecules of solute and carry them
away.
Most of the time, substances
dissolve faster at higher
temperatures.
This is because high temps have
more energy and are more effective
at knocking molecules apart.
P182
Solubility: the amount of solute that
can dissolved in a specific volume
under certain conditions.
Ex: 200 grams of sugar can be
dissolved in 100mL of water at 25*C
Solubility is always given at specific
temperatures since temperature
strongly affects solubility.
At 25*C, per 100mL of water:
Table Salt (NaCl) – 37.7 grams
Sugar (C12H22O11) – 200 grams
Baking Soda (NaHCO3) – 10 grams
Chalk (CaCO3) – insoluble
Talc (Mg silicate) – insoluble
Insoluble: a substance that does not
dissolve in a particular solvent
Chalk and Talc do not dissolve in
water; it would just be a mixture of
chalk and water.
Saturation: a solution is saturated if
it contains as much solute as the
solvent can dissolve.
Ex: if you add 300 grams of sugar to
100mL of water at 25*C, only 200
grams will dissolve. You will be left
with 100grams of solid sugar at the
bottom of your solution.
P183
Concentration – the ratio of solute
to solvent in a solution
E: 10% sugar solution contains
10grams of sugar for every 90grams
of water.
Concentration = mass of solute
Total mass of solution
x100%
Very low concentrations:
Parts per million (ppm)
Parts per billion (ppb)
Parts per trillion (ppt)
Commonly used to describe very
small concentrations of pollutants in
the environment.
These terms are measures of the
ratio by mass of one material in a
much large amount of another.
EPA.GOV – in drinking water
Arsenic – 10 ppb
Lead – 15 ppb
Copper – 1.3 ppm
Ex: a pinch of salt in 10 tons of
potato chips is about 1 gram of salt
per billion grams of chips 1ppb
P184:
Equilibrium: occurs when a solution
has the maximum concentration of
dissolved solute
Supersaturated: a concentration
greater than the maximum solubility
When a solute like sugar is mixed
with a solvent like water, TWO
processes are actually going on
continuously.
1. Molecules solute dissolve and go
into solution
2. Molecules of solute come out of
solution and become “un-dissolved”
The higher the concentration, the
faster molecules come out of
solution. The un-dissolving process
gets faster until the dissolving and
un-dissolving rates are equal.
At equilibrium, a solution is
SATURATED because the
concentration is as high as it can go.
At 80*C, 100 grams of water can
dissolved 360 grams of sugar.
If this is cooled back down to 25*C,
there is more dissolved solute than
the maximum solubility.
Growing crystals:
A supersaturated solution is
unstable. This is how large sugar
crystals of rock candy are made.
Sugar is added to boiling water until
the solution is saturated. As it cools,
it becomes supersaturated. Solid
sugar crystals form.
P185 – The solubility of gases and
liquids
Gases can also dissolve in liquids.
When you drink carbonated soda,
the fizz comes from dissolved
carbon dioxide gas (CO2)
The solubility of gases in liquids
increases with pressure. Soda is
fizzy because the carbon dioxide was
dissolved in the liquid at high
pressure. When you pop open the
can of soda, you release the
pressure. The solution immediately
becomes supersaturated, causing
the CO2 to bubble out of the water
and fizz.
Oxygen can dissolve in water.
Dissolved oxygen keeps fish and
other underwater animals alive.
Just like on land, oxygen is produced
by underwater plants using
photosynthesis.
When temperature goes up, the
solubility of gases in liquid goes
down. When the water temperature
rises, the amount of dissolved
oxygen decreases.
When weather is warm, fish stay
near the bottom of ponds and rivers
where there is cooler, more
oxygenated water.
Some liquids, such as alcohol, are
soluble in water. Other liquids, like
corn oil, are not.
Oil and vinegar (water solution)
salad dressing separates because oil
is not soluble in water.
But oil is soluble in other solvents,
like petroleum-based paint thinners.
P 186
Water is often called the “universal
solvent.” It doesn’t dissolve
EVERYTHING, but it does dissolved
many different types of substances.
Water is a good solvent because of
the way the H2O molecule is shaped!
Polar – describes a molecule that
has a positive and negative charge
separation.
A water molecule has a positive end
and a negative end.
The oxygen side has a partially
negative charge, and the hydrogen
side has a partially positive charge.
How water dissolves salt:
Remember that salt is an ionic
compound (Na+Cl-)
The negative ends of the water
molecules are attracted to the Na+
ions and the positive ends are
attracted to the Cl- ions. Water
molecules surround the Na+ and the
Cl- and cause the salt crystal to
separate and make a solution.
How water dissolves sugar, a
covalent compound:
Individual molecules of sugar
become separated from each other
and are attracted to the opposite
poles of the water molecules. Sugar
remains neutral in the solution, not
ionic.
Oil does not dissolve in water
because water is a polar molecule
and oil molecules are non-polar.
oil and water
So, water, a polar molecule can only
dissolve other polar substances.
Non-polar solvents dissolve nonpolar substances.