Solubility and
Solubility curves
Solubility
• The solubility of a substance is the mass
required to make a saturated solution in a
given quantity of solvent (usually water) at a
certain temperature.
• Solubility at a given temperature = maximum
mass (g) of a substance that will dissolve in
100 ml of water.
• For example at 20°C, the solubility of
potassium nitrate is 32 g per 100 g of water.
Solubility of a substance is
affected by…
1) The nature of the substances
For example, ionic compounds and hydrates
dissolve in aqueous solutions.
2) The polarity of the substances
For example, polar substances dissolve in polar
solvents.
3) The temperature
Some substances only dissolve above certain
temperatures.
4) The pressure
Some substances only dissolve when under
pressure.
Solubility of a solid - KClO3
Mass Temp Mass Temp
3
0
30
69
10
28
35
76
15
40
40
83
20
52
45
87
25
60
50
93
Draw a graph of
the maximum
mass of KClO3
dissolved vs.
temperature
Solubility curve for KClO3
g / 100
ml Hg20
g solute10/ 100
60
50
40
30
20
10
0
0
10 20 30 40 50 60 70 80 90
Temperature (*C)
Solubility types
• Saturated solution – a solution containing the
maximum quantity of solute at a specific
temperature and pressure
• Unsaturated = ?
A solution containing less than the maximum
quantity of solute possible for that solvent at a
specific temp. and pressure.
• Supersaturated – ?
A solution containing more solute than the
saturated conditions.
Fig 2 on page 316 Questions
3. To make a saturated solution of KClO3, how much KClO3 is
dissolved in 100 ml of water at (i) 20°C (ii) 40°C (iii) 60°C
4. What minimum temperature is needed to dissolve these masses of
KNO3 (not KClO3) in 100 ml H2O: (i) 46 g (ii) 15 g (iii) 80 g
5. What type of solution (saturated or unsaturated) forms when ___ g
of KClO3 are dissolved in 100 ml of H2O at ___°C:
(a) 43 g, 85°C, (b) 32 g, 85°C, (c) 10 g, 60°C.
6. 100 ml H2O is saturated with KClO3 at 100°C. How much KClO3
will come out of solution if the temperature is lowered to 48°C?.
How much would precipitate under the same circumstances if 350
ml water were used?
7. A saturated solution of potassium nitrate is cooled from 50°C to
10°C. How many grams of KNO3 will precipitate out of 150 ml of
water?
3a i) 7
ii) 14
iii) 24 - 25
3b i) 30°C
ii) 3°C
iii) 48°C
g solute
per
100
mlgHH2O
/ 100
g solute
20
Results of lab: solubility of KClO3
4 i) saturated
ii) unsaturated
iii) unsaturated
80
70
60
50
40
30
20
10
0
KNO3
Supersaturated
4 i)
4 ii)
4iii)
Unsaturated
0
20
40
60
80
Temperature (oC)
10
Saturation and solubility curves
See Fig 2 on pg. 316
Notice that there are solubility curves for many
different substances
Q - Why do temperatures range from 0-100°C
A - Water is a liquid at these temperatures
Solubility curves tell us how much solid will
dissolve at a given temperature
They also allow certain calculations…
Calculations using solubility curves
Using fig 2 (pg. 316)
5. 100 ml H2O is saturatedwith KClO3 at 100°C.
How much KClO3 will come out of solution if
the temperature is decreased to 48°C?
57 g - 18 g = 39 g
How much would precipitate under the same
circumstances if 350 ml water were used
(57 g - 18 g) x 3.5 = 137 g
6.
(85 g - 21 g) x 1.5 = (64 g) x 1.5 = 96 g
Solubility of gases
• Read page 319 of text ‘Solubility in
water – Generalizations and examples’