1. Solubility Curves
SCH 3U

2. Learning Goals By the end of this lesson students will be able to:
Use appropriate terminology related to aqueous solutions and solubility
Explain the effects of changes in temperature on the solubility of solids, liquids, and gases
Analyse quantitative properties of solutions

3. Saturation Demo!

4. Solubility
Saturated- solution contains all the solute it can hold at a given temperature
Unsaturated- contains less solute than it can hold under existing conditions
Supersaturated- contains more solute than it would normally hold at a given temperature; usually not stable, may cause solution to crystallize and precipitate out of solution

5. Solubility

6. Solubility Factors Molecule Size and Solubility Pressure Temperature
Larger molecules of the solute = larger molecular mass and size
Therefore it is more difficult for solvent molecules to surround bigger molecules
Pressure
Solid & Liquids: pressure = little effect
Solubility of gas is directly related proportional to the pressure of the gas above the liquid
Temperature
Solids: Temperature Increase = increases solubility
Liquids: Temperature Increase = little effect
Gas: Temperature increases = decreases solubility
Surfactant - compound like soap which reduces the surface tension with both hydrophobic and part hydrophilic helps break down hydrogen bonds and allow water to form around the oil particles
Pressure is a force exerted by the substance per unit area on another substance. The pressure of a gas is the force that the gas exerts on the walls of its container.

7. Temperature And Solubility
Solubility of Solids:
When a solid dissolves in a liquid, energy is needed to break the bonds between particles in a solid
Higher temperatures = greater energy
Example:
Caffeine's solubility in water is only 2.2g/100mL at 25oC
Caffeine's solubility in water increases to 40g/100mL at 100oC

8. Temperature And Solubility
Solubility of Liquids:
The bonds between liquids are not as strong as the bonds between particles in solids
When a liquid dissolves in a liquid, additional energy is not needed

9. Temperature And Solubility
Solubility of Gases:
Gas particles move quickly and have higher kinetic energies than liquids
When a gas dissolves in a liquid it loses energy
Increasing temperature = increases kinetic energy
Increase in kinetic energy allows greater movement in the gas particles resulting in the gas coming out of solution
process is exothermic

10. Temperature And Solubility
Conclusion:
A solid becomes more soluble as temperature increases.
A liquid’s solubility is not greatly affected as temperature increases
A gas becomes less soluble as temperature increases.
Slope: A steeper slope reflects
more of an effect on solubility
as temperature increases.

11. Solubility Curves Solubility curves have:
Solubility is plotted on the y axis
Usually in units of g/100mL
Temperature on x axis
In Units of degrees Celcius
Lines represent saturated solution

12. Saturation of Solutions
Any point on the line would be a saturated solution
Any point below the line, unsaturated
Any point above the line, supersaturated
Any solution can be made saturated, unsaturated or supersaturated by changing the temperature

13. Sample Problem 1
Solubility curves allow us to determine the amount of a solute that can dissolve in 100 grams of water at a given temperature.
How to read the data:
What amount of KCl dissolved in 100 grams of 90oC?
50g dissolve per 100 ml
At what temperature is the solubility of NaCl 40.0g/100g?

14. Sample Problem 2 How much KCl would dissolve in 500 ml @ 90oC?
50g = xg
100ml ml
x = 50g x ml
100ml
x = 250 g

15. Sample Problem 3
A saturated solution of KNO3 in 200 g of water at 50°C is cooled to 20°C. How much KNO3 settles out? 

@50oC: 90g = xg
100ml 200g
x = 180g
@20oC: 35g = xg
100ml g
x = 70g
180g - 70g = 110g of KNO3 settle out

16. Homework
Solubility Curve Worksheet