1. Titration Basics
Titration = addition of a measurable volume of a known solution (titrant) to an unknown solution until it is just consumed
Use the stoichiometry of the reaction of the known and unknown to calculate the concentration of the unknown solution
A pH curve shows the change in pH versus volume of titrant as the titration proceeds
pH meter can be used to monitor
pH during the titration
2) An acid-base indicator can be used
to signal reaching the equivalence point
First Derivative Curve
Shows where change is greatest

2. 3) Important points:
pH increases slowly far from the equivalence point
pH changes quickly near the equivalence point
The equivalence point of a strong acid—strong base titration = 7.00
4) The titration of a strong base with a strong acid is almost identical

3. Titration of a Weak Acid with a Strong Base
Addition of a strong base to a weak acid forms a Buffer Solution
HA OH A H2O
If not enough base has been added to complete the reaction: HA/A- buffer
B. Important Points
pH increases more rapidly at the start than for a strong acid
pH levels off near pKa due to HA/A- buffering effect
pH = pKa + log([A-]/[HA]) = pKa + log(1) = pKa (when [A-] = [HA])
Curve is steepest near equivalence point. Equivalence Point > 7.0
Curve is similar to strong acid—strong base after eq. pt. where OH- is major
½ Equivalence Pt.
pH = pKa
12.5

4. Titration of a Weak Base with a Strong Acid
Similar problem to the titration of a weak acid with a strong base
Determine major species from the stoichiometry
Calculate pH from weak acid, buffer, or weak base accordingly
Example: Titrate 100 ml of 0.10 M NH3 (Kb = 1.8 x 10-5) with 0.1 M HCl.

5. IV. Titrations of Polyprotic Acids and Bases
Multiple Inflection Points = Multiple Equivalence Points will be seen
The volume required to reach each equivalence point will be the same
CO H HCO Kb1 = KW/Ka2 = 1.8 x (pKb1 = 3.74)
HCO H H2CO Kb2 = KW/Ka1 = 2.3 x (pKb2 = 7.64)
½ Eq. pt Eq. pt ½ Eq. pt Eq. pt 2
pKa2 = 10.26
pKb1 = 3.74
pKa1 = 6.36
pKb2 = 7.64

6. Acid-Base Indicators Finding the equivalence point of a titration
Use a pH meter
Plot pH versus titrant volume
Center vertical region = equivalence point
Use an Acid-Base Indicator
Acid-Base Indicator = molecule that changes color based on pH
Choose an indicator that changes color at the equivalence point
End Point = when the indicator changes color. If you have chosen the wrong indicator, the end point will be different than the eq. pt.
Indicators are often Weak Acids that lose a proton (causing the color change) when [OH-] reaches a certain concentration
HIn OH In H2O

7. B. We can use the Henderson-Hasselbalch equation on Indicators as well
pH = pKa log([In-]/[HIn])
pH = pKa log(1/10) for a color change
log(1/10) = -1
pH for color change starting in acid is always pKa – 1 for any Indicator
For a basic solution titrated with acid, [In-]/[HIn] = 10/1 for color change
Log(10/1) = +1, pH for color change will equal pKa + 1
Useful range for a pH Indicator is always pKa +/- 1