3.2 Solubility

Chemistry
Chapter 3 - Section 2

Solubility



Water – The Universal Solvent
•Many solutions have water as
the solvent.
•These solutions are called an
aqueous solution.
•Water dissolves many solutes
and so scientists call it the
universal solvent.
•Why is water such a great
solvent? Let’s ﬁnd out.

Dissolving an Ionic Compound
example: NaCl

The positive area of the water molecules surround
the negative Chloride ions.

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The negative area of the water molecules
surround the positive sodium ions.

As the attractions from the water molecules and
their motion pulls the ions apart, the sodium
chloride crystal dissolves.

Dissolving a Molecular Compound

Dissolving a Molecular Compound
example: sugar

Water molecules arrange themselves around the
sucrose molecules according to opposite polar
areas.

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The attraction of the water molecules and their
motion overcome the attraction between sucrose
molecules.

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The sucrose molecules dissolve as they are
separated from the other molecules and mix into
the water.

13

The sucrose molecules dissolve as they are
separated from the other molecules and mix into
the water.

What will
dissolve?
The spoon
or the
sugar??

Like Dissolves Like
•Polar solvents will dissolve polar solutes.
•Nonpolar solvents will dissolve nonpolar
solutes.

•Polar will not dissolves nonpolar and vice versa.
•Think about oil and water. Is the oil polar or
nonpolar?

How Much Will
Dissolve?

•If you tried to dissolve a lot of sugar in a small glass
of water, not all of the sugar would dissolve.

•Solubility is the measurement of how much
solute dissolves in a given amount of solvent.

•Solubility is usually describes as how much can
dissolve in 100g of solvent at a given temperature.

Solubility
in a
Liquid-Solid
Solution
Temperature is
included here
because the
solubility of a
solute changes as
the temperature of
the solvent
changes.

Solubility
in a
Liquid-Solid
Solution
As you heat
water, you can
dissolve sugar in
water faster rate,
but also more
sugar will
dissolve.

Solubility
in a
Liquid-Gas
Solution
In a liquid-gas solution,
the opposite is true.

As the temperature
increases, the solubility
decreases.

Solubility
in a
Liquid-Gas
Solution
This is because the
water molecules will
be moving faster at
higher temperatures.
This movement will
bump the gas out of
the solution, therefore
decreases solubility.

Saturated Solutions
•If you add calcium
carbonate to 100g of water
at 25˚C, only 0.0014g will
dissolve. No more can
dissolve.
•This solution is called a
saturated solution.
•If the solution was a liquid-
solid solution, the extra solid
would settle on the bottom
of the container.

Saturated Solutions
•The solubility of sugar in 100g of water at
25˚C is 204g.
•If you had a solution with 50g of sugar in 100g
of water, the solution is called unsaturated.
More solute could dissolve.

Saturated Solutions
•A hot solvent can
usually hold more
solute then a
cooler one.
•If a saturated
solution cools, some
of the solute can fall
out of the solution.

Saturated Solutions
•A hot solvent can usually hold more solute then
a cooler one.
•If a saturated solution cools, some of the solute
can fall out of the solution.
• But if the solution is cooled slowly,
sometimes the excess solute remains dissolved for
a period of time. This solution is called
supersaturated.

Rate of Dissolving
•Solubility does not tell you how fast a solute will
dissolve.
•Some solutes will dissolve quickly, others take a long time
to dissolve.
•A solution dissolves faster when:
✴it is stirred
✴it is shaken
✴the temperature is increased

•How exactly do these factors help?
✴They increase the rate at which the surfaces of the

solute come into contact with the solvent.
✴Increasing the area of contact between the solute

and the solvent can also increase the rate of
dissolving

Concentrated!
•The concentration of a solution tells you how
much solute is present compared to the amount of
solvent.
•When you are comparing the concentrations of
two solutions with the same type of solute and
solvent, you can use a simple description such as:
dilute or concentrated.

Concentrated!

•The Dead Sea is
5+ times saltier than
Earth's oceans. As
water evaporates,
salt is left behind.
When the
saturation point is
reached, the salt
forms these pillars.

Measuring
Concentrations
•One way to give the
concentration is by using the
percentage of the volume
of the solution that is made
up of the solute.

Effects on Solute Particles
•Solute particles affect the physical properties
of the solvent, such as the boiling point or the
freezing point.

•Adding a solute, such as NaCl, changes the way
the water molecules can arrange themselves. The
solute gets in the way.

•To overcome this interference of the solute, a
lower temperature is needed for the solvent to
freeze.


•When a solvent begins to boil, the solvent
molecules are gaining enough energy to move
from the liquid state to the gaseous state.


•When a solute is introduced, its particles
interfere with the evaporation of the solvent
particles.


•For water and NaCl, the NaCl will block the
H2O from escaping the liquid and becoming a
gas.


•More energy is needed for the solvent
particles to escape from the liquid, and the
boiling point of the solution will be higher.

3.2 Solubility

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3.2 Solubility

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