TITRATION CURVES
UNIT 5 CH40S WIEBE
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Titration Curves: Understanding pH Changes in Acid-Base Reactions, Study notes of Stoichiometry
An introduction to titration curves, explaining the concept of pH changes during acid-base titrations and the significance of equivalence and endpoint points. It covers three types of titration reactions: strong acid and strong base, weak acid and strong base, and strong acid and weak base. The document also includes instructions on choosing indicators and matching titration curves with reactions.
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TITRATION CURVES
UNIT 5 CH40S WIEBE
A titration curve is a graph of the pH changes that occur during an acid-
base titration versus the volume of acid or base added.
The equivalence point is the end of a titration where the stoichiometry
of the reaction is exactly satisfied, or moles H
+ = moles OH
- .
The end point refers to when an indicator changes color and [HInd] =
[Ind
- ].
Titration Curves
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 Dominant Equivalence Point
Neither 7
Base 9
Acid 5
Choosing an Indicator
- Titration Curve: Strong Acid and Strong Base
HCl + KOH → KCl + HOH
Endpoint pH = 7 Bromothymol Blue- see page 7
50 mL of 0.10 M KOH is added to 25 mL of 0.10 M HCl
pH
Volume .10 M KOH added
14
7
0
0 25 50
0.10 M HCl
Endpoint pH = 7.
0.10 M KOH
We start here
The pH of 0.10 M HCl is 1. The pH of 0.10 M KOH is 13.
- Titration Curve: Strong Acid and Weak Base
HCl + NH 3
→ NH
4
- Cl
- strong acid dominates!
Endpoint pH ~ 5 Methyl Red- see page 7
60 mL of 1.0 M NH 3
is added to 30 mL of 1.0 M HCl
pH
Volume 1.0 M NH 3
added
14
7
0
0 30 60
1.0 M HCl pH = 0
Endpoint pH 5
1.0 M NH
3
pH 10 (weak base)
pH
Volume .10 M KOH added
14
7
0
0 25 50
- Match the Curve with the Reaction
A. HCl + NH 3
→ NH
4
- Cl
B. HCl + KOH → KCl + HOH
C. HCN + KOH → KCN + HOH
pH
Volume 1.0 M NH 3
added
14
7
0
0 30 60
6. Match the Curve with the Reaction
A. HCl + NH 3
→ NH
4
- Cl
B. HCl + KOH → KCl + HOH
^ C.^ HCN^ +^ KOH^ →^ KCN^ +^ HOH