Solutions can be classified as saturated or
unsaturated.
A saturated solution
It’s a solution in which no more solute can dissolve
at that temperature (It contains the maximum
quantity of solute that dissolves at that
temperature)
An unsaturated solution
It’s a solution in which more solute can dissolve at
that temperature (it contains less than the
maximum amount of solute that can dissolve at that
particular temperature)
• What is the solubility of a substance?
It is the maximum mass of a substance that
dissolves in 100g of water at a particular
temperature
e.g. maximum mass of sodium chloride that
dissolve in 100g of water at 30oC is 38g.
So the solubility of sodium chloride in water at
30oC is 38g per 100g of water
Solubility curve
• It’s a curve that shows the solubility of a
substance at different temperatures of the
solvent.
X axis – temperature
Y axis – solubility in g per 100g of water
• The points on the curve shows the maximum
amount of the substance that dissolve in 100 g
of water at that temperature
Solubility of solids with temperature
• More solid can dissolve in a solvent at higher
temperatures
• If a saturated solution is heated it becomes
unsaturated because more solute could dissolve
when temperature is increased.
• If a saturated solution is cooled down, some
solute crystallises out of the solution because less
solute could dissolve when temperature is
decreased.
Solubility of gases with temperature
• less gas can dissolve in a solvent, at higher
temperatures.
• As the temperature rises, gases become less
soluble in water
e.g: When warm water is released into water
bodies, it increases the temperature of water and
decreases the amount of dissolved oxygen. Fish die
due to lack of oxygen
Temperature
(oC)
0
20
40
60
80
90
3
8
14
24
38
44
Solubility/ g per
100g of water
Potassium chloride dissolves in water. Use the data given below to plot
a solubility curve for potassium chloride
Using your graph, answer the following questions.
i) What is the relationship between the temperature and the
solubility of potassium chloride?
ii) What mass of potassium chloride dissolves in 100g of water at 50oC?
50
45
40
35
30
25
20
15
10
5
0
0
10
20
30
40
50
60
70
80
90
100
iii) What is the lowest the lowest temperature at
which 30g of potassium chloride will dissolve in
100g of water?
iv) If a saturated solution of potassium chloride in
100g of water at 60oC, is cooled down to 10oC,
how much potassium chloride will crystallise?
v) If a saturated solution of potassium chloride in
100g of water at 50oC is heated up to 80oC, how
much more potassium chloride can dissolve?