1. Titration and pH Curves.

2. Weak Acid-Strong Base Titration Curves.
Before the addition.
Construct an “equilibrium” reaction table ONLY!
Ka = [A-] [H3O+] to obtain [H3O+].
[HA]
 Calculate the pH.

3. Weak Acid-Strong Base Titration Curves.
Additions before the equivalence point.
Construct a stoichiometry reaction table.
Determine MOLES of acid in excess (not neutralized) and MOLES of conjugate base formed.
Divide MOLES by the TOTAL VOLUME to obtain [H3O+] and [A-].
Construct an “equilibrium” reaction table.
 Ka = [A-] [H3O+] and obtain [H3O+].
[HA]
 Calculate the pH.

4. Half equivalence point
The equivalence point is when the moles or titrant are equal to the moles of analyte.
At half the equivalence point, exactly half of the weak analyte will be shifted into it’s conjugate.
HA ⇌ H+ + A-, therefore [HA] = [A-]
pH = pKa + log ([A-]/[HA])
At the half equivalence point
pH = pKa

5. Additions at the equivalence point.
Construct a stoichiometry reaction table.
 Determine MOLES of conjugate base formed. Divide MOLES by the TOTAL VOLUME to obtain [A-]. Calculate Kb
(Ka x Kb = Kw).
Construct an “equilibrium” reaction table, reacting the conjugate base with water.
Kb = [OH-] [BH+] and obtain [OH-].
[B]
Calculate the pOH, then the pH.
The equivalence point is ALWAYS >7!

6. Additions beyond the equivalence point
Construct a “stoichiometry” reaction table.
Determine MOLES of base in excess (not neutralized) and the MOLES of conjugate base.
Divide MOLES by the TOTAL VOLUME,
 Because [OH-]excess >> [OH-]conj. base, use [OH-]excess to calculate pOH, then the pH.

7. Problem
50.0 mL of 0.10 M CH3COOH, acetic acid (Ka = 1.8 x 10-5) are titrated with 0.10 M NaOH. Calculate the pH after the additions of 0, 10.0, 25.0, 40.0, 50.0, 60.0, and 75.0 mL samples of NaOH.
Then, construct a titration curve and label it properly.

8. Problem
50.0 mL of 0.20 M H2CO3, carbonic acid (Ka = 4.4 x 10-7) are titrated with 0.20 M NaOH.
Calculate the pH after the additions of 0, 10.0, 25.0, 40.0, 49.0, 49.95, 50, 50.05, 51.0, 60.0, and 75.0 mL samples of NaOH.
Then, construct a titration curve and label it properly.