1. Titration Curve B.Sc. Sneha S. Mule Assistant Professor
Department of Chemistry,
S. M. Joshi College, Hadapsar

2. A titration curve is a plot of pH vs. the amount of titrant added
A titration curve is a plot of pH vs. the amount of titrant added. Typically the titrant is a strong (completely) dissociated acid or base. Such curves are useful for determining endpoints and dissociation constants of weak acids or bases.
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 An acid-base indicator can be used to signal reaching the equivalence point
Equivalence Point: the point at which the amount of titrant add is exactly equal to the amount needed to give stoichiometric consumption of the analyte
End Point: the point at which the amount of titrant produces an observable change during the titration, signaling the complete or near complete consumption of analyte (the actual case)

4. pH increases slowly far from the equivalence point
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
The pH starts out low, reflecting the high [H3O+] of the strong acid and increases gradually as acid is neutralized by the added base.
Suddenly the pH rises steeply. This occurs in the immediate vicinity of the equivalence point. For this type of titration the pH is 7.0 at the equivalence point.
Beyond this steep portion, the pH increases slowly as more base is added.

6. 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

7. 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

8. 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

9. The loss of each mole of H+ shows up as separate equivalence point (but only if the two pKas are separated by more than 3 pK units).
The pH at the midpoint of the buffer region is equal to the pKa of that acid species.
The same volume of added base is required to remove each mole of H+.

10. 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

11. THANK YOU