1. SOLUTIONS AND SOLUBILITY
UNIT 4:
SOLUTIONS AND SOLUBILITY

2. CHARACTERISTICS OF SOLUTIONS & THE DISSOLVING PROCESS
Section (8.2 & 8.3)
CHARACTERISTICS OF SOLUTIONS & THE DISSOLVING PROCESS

3. What is a Solution?
Solutions are homogeneous mixtures of two or more pure substances.
Substances can be dissolved into one another, resulting is a uniform distribution
Solutions are homogeneous mixtures of two or more pure substances.
They can be made by dissolving a substance in another, resulting in a uniform distribution.
This means that if you took any two samples of the same solution, you will find they contain the same substances in the same relative amounts.

4. Types of Mixtures E.g. sand in water E.g. salt in water
This means that if you took any two samples of the same solution, you will find they contain the same substances in the same relative amounts.
Example: sand in water vs. salt in water
E.g. sand in water
E.g. salt in water

5. Solute vs. Solvent All solutions have a solute and a solvent
The solute is the substance that get dissolved
The solvent does the dissolving
No chemical reaction occurs!
Aqueous solutions are produced when water is the solvent
solute
When a solute is dissolved into a solvent, no chemical reaction occurs
What if you have two liquids, which one is the solvent? The liquid present in the largest amount is considered the solvent and the liquid with the smaller volume is the solute.
solvent

6. Types of Solutions Solutions can be composed of various states.
More examples on page 379

7. Miscible vs. Immiscible
Miscible: liquids that will dissolve in each other
Immiscible: liquids that will not readily dissolve in each other
Another example is oil and water

8. Immiscible Mixtures

9. The Process of Dissolving
At the molecular Level: Step 1: The forces between the particles in the solid (solute) must be broken. Step 2: Some of the intermolecular forces between the particles of the liquid (solvent) must be broken. Step 3: There is an attraction between the particles of the solute and the particles of the solvent. Step 4: Particles are rearranged to form a homogeneous solution
The reasons why a a solute may or may not dissolve in a solvent are related to the forces of attraction between the solute particles and the solvent particles. When the forces of attraction between different particles in a mixture are stronger than the forces of attraction between like particles in the mixture, a solution forms
At the molecular Level:
Step 1: The forces between the particles in the solid (solute) must be broken. In an ion solid, the forces that are holding the ions together must be broken. In a molecular solid, the forces between the molecules must be broken.
Step 2: Some of the intermolecular forces between the particles of the liquid (solvent) must be broken.
Step 1 and step 2 are both endothermic, as they require energy.
Step 3: There is an attraction between the particles of the solute and the particles of the solvent. This step is exothermic as it gives off energy.
The solute is more likely to dissolve if the energy change in step 3 is greater than the sum of the energy changes in step 1 and 2.

10. The Dissolving Process

11. Dissociation Equations:
Only for ionic compounds
Solid compound  component ions (aq)
Ex. NaCl(s)  Na+(aq) + Cl-(aq)
CaBr2(s)  Ca+2(aq) Br-(aq)
You Try:
K3PO4(s) 
Al2(SO4)3(s) 

12. Polarity and Solubility
Not everything will dissolve in a solvent.
So how to you predict a good solvent?
Polar solutes will dissolve polar solvents
Non-polar solutes will dissolve non-polar solvents
LIKE dissolves LIKE

13. Recall: Dipole Attractions
Attraction between the opposite charges on two different polar molecules.
This means they act between molecules
Dependant on the difference in electronegativity between two atoms.

14. Recall: Hydrogen Bonding
A special type of dipole attraction
Intermolecular attraction between molecules containing a hydrogen atom, bonded to another atom that is highly electronegative.

15. Recall: Ion-Dipole Attraction
Process for dissolving Ionic Compounds
Attraction between an ion and a polar molecule.
Ions in a aqueous solution are considered hydrated, and have the ability to conduct electricity.
A solute that forms an aqueous solution with the ability to conduct electricity is called an electrolyte.

16. Solubility & Saturation
Section (8.5)
Solubility & Saturation

17. Saturation of a Solution
A saturated solution is formed when no more solute will dissolve in a solution, and excess solute is present
It has the maximum amount of solute it can hold
An unsaturated solution is a solution that is not yet saturated. It can still dissolve more solute

18. Solubility Solubility is defined as:
The amount of solute that dissolves in a given quantity of solvent, at a certain temperature, to form a saturated solution
Usually stated in grams of solute per 100 g of water at a given temperature.
E.g. the solubility of sodium chloride in water at 20°C is 36g per 100mL of water
Insoluble if solubility < 0.1g per 100 mL solvent

19. Solubility Recall, solubility defined as:
The amount of solute that dissolves in a given volume of solvent, at a specific temperature, to form a saturated solution.
For most solids:
as T increases, solubility increases
For most gases:
as T increases, solubility decreases
as P decreases, solubility decreases

20. Factors that Affect Rate of Dissolving
Particle size: Finely divided substances have more surface area and dissolve more rapidly
Motion: Stirring or shaking brings more solvent in contact with more solute particles, increasing solubility
Temperature: The solubility of most solids increases with temperature. The solubility of gases decreases with temperature.
It is important to note that the rate, at which a substance dissolves, does not alter the substance's solubility. If a solute is not soluble in a certain solvent, changing the conditions will not make it dissolve in the solvent.

21. Summary of Factors that Affect Solubility
The polarity of the substances:
LIKE dissolves LIKE
The nature of the substances:
Intermolecular bonds
The temperature:
Some substances only dissolve above certain temperatures
The pressure:
Some substances only dissolve under pressure

22. Solubility Curves
It is possible to represent solubility visually by graphing the solubility of substances in function of temperature. The following graph, called a solubility curve, depicts the solubility of nine substances in water. Each substance is represented by its own coloured line. You will be asked to solve problems based on interpreting this graph.

23. Using Solubility Curves
Which salt is least soluble at 40°C?
NaCl
K2Cr2O7
KClO3
KNO3
Which of the following decreases in solubility as the temperature increases?
KCl
Ce2(SO4)3
NaNO3

24. Using the Solubility Graph
How many grams of lead (II) nitrate, Pb(NO3)2 are soluble in 100g of water at 30°C?
40g
45g
65g
130g
At what temperature does the solubility of sodium chloride match the solubility of potassium chlorate?
25°C
60°C
90°C
100°C

25. Using the Solubility Graph
When 70 g of calcium chloride are dissolved in 100 g of water at 20°C, the solution can be described as:
saturated
unsaturated
A solution of potassium chloride has 35g of the salt dissolved in 200 g of water at 60°C. How many more grams of the salt can be added to the solution before reaching the saturation point?
none, it is already saturated
15g
25g
50g