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+]?

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

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.

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

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

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