3. Titration Curves
A titration curve is a graph of the pH versus the volume in a titration.
The equivalence point is the end of a titration where the stoichiometry of the reaction
is exactly satisfied. moles H+ = moles OH-
The transition point is when an indicator changes color and [HInd] = [Ind-].
4. Choosing an Indicator
When you choose an indicator, you must pick one so that the transition point of the
indicator matches the equivalence point of the titration.
Rule of thumb Salt Equivalence Point
Neutral 7
Basic 9
Acidic 5
5. 1. Titration Curve: Strong Acid and Strong Base
pH
Volume 0.10 M KOH added
14
7
0
0 25 50
We start here
neutral salt pH = 7 Bromothymol Blue- see page 7 data
50 mL of 0.10 M KOH is added to 25 mL of 0.10 M HCl
HCl + KOH → KCl + HOH
is added to
6. 2. Titration Curve: Weak Acid and Strong Base
HCN + KOH → KCN + H2O basic salt
Indicator pH = 9 Phenolphthalein- see page 7 data
20 mL of 1.0 M HCN is added to 10 mL of 1.0 M KOH
pH
Volume 1.0 M HCN added
14
7
0
0 10 20
is added to
7. 3. Titration Curve: Strong Acid and Weak Base
HCl + NH3 → NH4Cl acid salt
Indicator pH = 5 Methyl Red- see page 7 data
60 mL of 1.0 M NH3 is added to 30 mL of 1.0 M HCl
pH
Volume 1.0 M NH3 added
14
7
0
0 30 60
8. pH
Volume .10 M KOH added
14
7
0
0 25 50
A. 3HCl + Al(OH)3 → AlCl3 + 3HOH
C. HCN + KOH → KCN + HOH
6. Match the Curve with the Reaction
B. HCl + KOH → KCl + HOH
9. pH
Volume 1.0 M NH3 added
14
7
0
0 30 60
B. HCl + KOH → KCl + HOH
C. HCN + KOH → KCN + HOH
6. Match the Curve with the Reaction
A. 3HCl + Al(OH)3 → AlCl3 + 3HOH
10. pH
Volume 1.0 M NH3 added
14
7
0
0 30 60
6. Match the Curve with the Reaction
A. 3HCl + Al(OH)3 → AlCl3 + 3HOH
B. HCl + KOH → KCl + HOH
C. HCN + KOH → KCN + HOH
