1. 8.2 Factors the Affect Solubility
Unit 4 - Solubility
8.2 Factors the Affect Solubility

2. Context – Review from Friday
Things dissolve in water if they can be attracted to water
Molecular compounds dissolve by being surrounded by water – the molecules themselves are not broken up
Ionic compounds dissociate into ions

3. Ionic Compounds in Water
Not all ionic compounds are soluble in water. It depends on the ionic bonds in the crystal lattice
Compounds with strong ionic bonds are hard to pull apart.
The water molecules will only be weakly attracted. The compound is insoluble.
Compounds with weak ionic bonds are easy to pull apart.
The water molecules are strongly attracted. The compound is very soluble.
Use the solubility chart
Dissolved ions are also called electrolytes – solution can conduct electricity

4. Solubility Categories
Highly soluble: when more than 1.0g of the substance will dissolve in 100mL of solvent
Slightly soluble: if between 0.1g – 1.0 g of substance will dissolve per 100mL
Insoluble: If less than 0.1g of solute will dissolve in 100mL
If something is soluble, there are certain factors that can change how soluble something is…

5. Factors that affect the RATE of dissolving
Temperature
Higher temperatures means greater kinetic energy, more collisions between solute and solvent
Agitation
More collisions with solute and fresh solvent
Particle Size
Increase the surface area for dissolution by grinding or crushing the solute into powder

6. Factors that Affect Solubility
Molecule Size
Small molecules are more soluble than large molecules
Temperature
Most solids have higher solubility at higher temperature
Doesn’t really affect liquid-liquid solubility
Gas solubility decreases at higher temperature

7. 3. Intermolecular Forces (molecules only!)
“Like dissolves Like”
4. Pressure (gases only!)
Changes in pressure do not affect liquid and solids
The solubility of gases is directly proportional to the pressure of the gas above the liquid

8. How much solute??
There is a limit to the amount of solute which can dissolve in a solvent
A solution which contains the maximum amount of solute is saturated
If the solution contains less than the maximum amount of solute, it is unsaturated
The crystals of solute added will continue to disappear.

9. If there is extra solute which cannot be dissolved, the solution is supersaturated
solid may and usually does come out of solution.
A change in temperature (cooling a solid dissolved in liquid) can cause a saturated solution to become supersaturated

10. As we know, the maximum amount of solute which a solution can dissolve depends on the temperature of the solvent
** Different trends for gases
We use a graph called a solubility curve to decide on masses

11. A solubility curve is a plot of solubility versus temperature.
The line represents a saturated solution.
Points below the line represent unsaturated solutions.
Points above the line represent a supersaturated solution.

12. Solubility Curve for Ionic Compounds

13. What is the solubility of potassium nitrate at 80ºC ?

14. At what temperature will sodium nitrate have a solubility of 95 g/100 cm3 ?

15. What is the solubility of sodium chloride at 25ºC in 100mL of water ?
From the solubility graph we see that sodium chlorides solubility is 36 g.

16. Solubility Curve for Gases
Solubility of gases in water shows an opposite trend!

17. Practice!
Worksheet
P. 289 # 9, 10
P. 301 # 1-4