1. Questions What is a strong acid? What is a weak acid?
Write expression for pH
HX(aq) + H2O(l)  X-(aq) + H3O+
For a strong acid like one above, what can you say about the concentration of [HX] and [H3O+]?

2. Water dissociation constant, Kw
Kw = [H3O+] x [OH-]
Increases with increased temperature
At 25 deg Kw = 1X10-14

3. CH3COOH + H2O n CH3COO- + H3O+
Weak Acids
Do not fully dissociate so:
Are in equilibrium biased to left
Have a low concentration of ions
Are poor conductors of electricity
React slowly as [H3O+] is low
CH3COOH + H2O n CH3COO- + H3O+
As they are in equilibrium, when they are diluted water concentration is increased and there is a shift to the right to compensate.
This means predicting pH increase is harder.

4. Acidity Constant, Ka Equilibrium constant Kc =
But water is a solvent so
So Ka =
[H3O+] [A-]
[HA] [H2O]
[H3O+] [A-]
[HA]
[H3O+] [A-]
[HA]

5. Weak acid pH Because So Ka = Rearrange and pH = -log[H3O+]
Now try Exercise 13C
[H3O+] = [A-]
[H3O+]2
[HA]
[H3O+]=
Ka x [HA]

6. pKa pKa= -logKa As the strength of acid increase Ka gets bigger
pKa gets smaller
Conjugate base gets weaker