1. Solubility and Solubility curves

2. 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.

3. 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.

4. Solubility of a solid - KClO3
30/09/99
Solubility of a solid - KClO3
Mass
Temp 3 30 69 10 28 35 76 15 40 83 20 52 45 87 25 60 50 93
Mass
Temp 3 30 10 35 15 40 20 45 87 25 50 93
Draw a graph of the maximum mass of KClO3 dissolved vs. temperature

5. 30/09/99
g solute / 100 ml H20

6. 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.

7. Results of lab: solubility of KClO3
30/09/99
Results of lab: solubility of KClO3
g solute / 100 ml H20
KNO3
3a i) 7
ii) 14
Supersaturated
4 i)
iii)
3b i) 30°C
Saturated
4 ii)
ii) 3°C
iii) 48°C
4iii)
Unsaturated
4 i) saturated
ii) unsaturated
iii) unsaturated

8. Saturation and solubility curves
30/09/99
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…

9. Calculations using solubility curves
30/09/99
Using fig 2 (pg. 316)
ml H2O is saturatedwith KClO3 at 100°C. How much KClO3 will come out of solution if the temperature is decreased to 48°C?
How much would precipitate under the same circumstances if 350 ml water were used 6.
57 g - 18 g = 39 g
(57 g - 18 g) x 3.5 = 137 g
(85 g - 21 g) x 1.5 = (64 g) x 1.5 = 96 g

10. Solubility of gases
Read page 319 of text ‘Solubility in water – Generalizations and examples’