Exp.2 Acid-Base Titration
Exp.2 Acid-Base Titration
Exp.2 Acid-Base Titration
Acid-Base titration
Objectives
There are many types of titration and the major type is:
(Acid-Base titration)
Evolution of the Burette
Acid - Base Titrations (Neutralization)
Titrations
In an acid-base titration experiment,
a solution of accurately known
molar concentration (Standard-
base) is added gradually from a
burette to another solution of
unknown concentration (Analyte-
acid) in a flask, until the chemical
reaction (Neutralization) between
the acid and the base is complete.
The end point of the reaction is
detected using an indicator.
Types of the indicators used in the titration
The indicator used in the titration depends on the type of the acid and base. The
selection of an indicator depends on the pH at the end point, therefore the indicator
changes its color within the pH at the endpoint. So any indicator mainly has three
colors, color before the pH range, color within the pH range and color after the pH
range.
Examples:
Remember: The type of indicator used in the titration depends on pH of the solution
Equivalence Point and End point
Equivalence-Point: the point at which the acid reacts (H+) completely with
the base (OH-).
OR, facid×(# of moles of acid) = fbase×(# of moles of base).
End-Point: the point at which the indicator changes its color, as a result the
color of the solution changed.
The difference between the two point (Experimentally) is few drops, so that
in the calculations the volume difference is ignored.
Remember:To minimize the drops difference between the end point and the
equivalence point, the color of the indicator at the end point should be very light
(the color that lasts only for less than 30 seconds with stirring).
Neutralization Reactions Definitions
Equivalence point: The point in the reaction at which mole of acid is equal
mole of base (If mole ratio 1:1).
OR, it’s the point at which the acid (H+) reacts completely with base (OH-).
End Point: the point at which indicator changes its color, therefore the color of
the solution changed.
At Equivalence point:
fHCl (Moles HCl) = fAl(OH)3 (Moles base) fHCl (M × V)HCl = fAl(OH) (M × V)AL(OH)3
3
Q2- A 0.0300 gm of a diprotic acid dissolved and diluted with distilled water then
titrated with 21.50 mL of 0.0311 M NaOH. Calculate the molar mass of the
diprotic acid.
facid (Moles acid) = fNaOH (Moles NaOH) facid (mass/MM) = fNaOH (M × V)NaOH
MM = 89.7 g/mol
Example: Titration of a Strong Acid with a Strong Base
H2SO4
H2SO4
Experiment Procedure
Titration of unknown concentration H2SO4 using standard NaOH
1. Clean a burette and rinse it with distilled water and fill the burette with the standard NaOH
solution given.
2. Make sure that the air bubbles are removed from the tip of the burette, and that the initial
reading is within the scale of the burette.
3. Rinse your 10.00 ml pipette with distilled water and then with about1 ml of the unknown
sulfuric acid solution.
4. Pipette a 10.00 ml of the unknown sulfuric acid into a clean 125 ml Erlenmeyer flask
5. Add about 25 ml of distilled water and 2 drops of phenolphthalein indicator to the flask.
6. Titrate the acid solution with standard NaOH solution.
7. The titration should be stopped as close to the end point as possible , that is , when
the first permanent pink color is observed.
8. Record the initial and the final volume readings of the NaOH on the report sheet.
9. Repeat procedures for two or more times in order to get atleast 3 precise results.
10. For each of these three titrations , calculate the molarity of the NaOH solution using the
formula.
11. Check that these molarity values differ by no more than 1%.
12. If not, repeat the titrations until three trials give a percent difference less than 1%.
Volume taken from the Burette
42.30 mL 21.30 mL
Report Sheet Average Molarity of the NaOH solution = M
(obtained From part one)
(Data) a. Titration of the unknown sulfuric acid:
Volume of the unknown sulfuric acid solution (Pipette) = mL