Form 6 Chemistry Experiment
Experiment 13
Name : __________________________ (
NKM
p.1/3
)
Date : ____________
Mark : ______
Determination of the Equilibrium Constant for Esterification
Aim
The purpose of this experiment is to determine the equilibrium constant of esterification
between ethyl ethanaote and propan-1-ol.
Introduction
In the presence of concentrated sulphuric(VI) acid, ethanoic acid reacts reversibly with
propan-1-ol when heated, forming propyl ethanoate and water.
The reaction equation and the equilibrium expression will not be given as you will be
asked to write these for yourself in the questions.
Requirements
Glacial ethanoic acid
propan-1-ol
0.50M NaOH
anti-bumping granules
concentrated sulphuric(VI) acid
phenolphthalein indicator
Quickfit set
balance
titration apparatus
1.0 cm3 graduated pipette
measuring cylinder
ice bath
Procedures
[Hazard Warning : Glacial ethanoic acid and concentrated sulphuric(VI) acid are corrosive,
propan-1-ol is flammable, and 0.5M sodium hydroxide is irritant.]
1. Put 0.25 mole of glacial ethanoic acid (density = 1.05 g cm-3) and 0.25 mole of propan-1-ol
(density = 0.8 g cm-3) into a clean, dry pear-shaped flask. Mix thoroughly.
2.
Titration 1 : Transfer 1.0 cm3 of the mixture by pipette to a 250 cm3 conical flask
containing about 25 cm3 deionized water and 2 drops of phenolphthalein indicator. Titrate
to end point (twice) with 0.50M sodium hydroxide solution. Record the mean titre (V1
cm3).
3.
Titration 2 : Add 8 drops of concentrated sulpuric(VI) acid to the remainder of the
acid-alcohol solution while continuously swirling the flask. Titrate (twice) another 1.0 cm3
sample immediately. Record the mean titre (V2 cm3). The difference between V1 and V2
represents the volume to be subtracted from subsequent titrations to correct for the amount
of sulphuric(VI) acid present.
4.
Titration 3 : Add a few anti-bumping granules to the flask, and attach it to a water-cooled
reflux condenser. Reflux for 45 minutes. Cool the flask and its contents first under
running tap water, then in an ice-bath. Remove 1.0 cm3 sample from the flask for titration
with the 0.50M sodium hydroxide as before. Record the titre needed and correct it for the
sulphuric(VI) acid.
5. Titration 4 : Continue refluxing for an additional half hour, cool, and titrate another 1.0 cm3
sample. The two titres should agree to within 0.2 cm3. Otherwise, repeat this step.
Form 6 Chemistry Experiment
Experiment 13
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Results Tables :
Titration 1
1
Final burette reading / cm
Mean titre / cm
1
3
3
3
V1 =
V2 =
Titration 3
1
Final burette reading / cm
Mean titre / cm
*
Titration 4*
2
1
2
3
Initial burette reading / cm
Volume delivered / cm
2
3
Initial burette reading / cm
Volume delivered / cm
Titration 2
2
3
3
3
If the mean titre in titrations 3 and 4 do not agree, reflux for another half hour and carry
out titration 5.
Questions
1.
What is the purpose of adding a small amount of concentrated sulphuric(VI) acid to the
reaction mixture at the beginning of the experiment ?
2.
Why should anti-bumping granules be added to the reaction mixture before refluxing ?
3.
Why should the refluxing be continued in step (5) until the titre of sodium hydroxide used
approaches constant ?
4.
Write the equation for the esterification reaction between ethanoic acid and propan-1-ol.
Form 6 Chemistry Experiment
Experiment 13
5.
Calculate the concentration of ethanoic acid remaining at the end of the reflux.
6.
Calculate the concentrations of the other species present at equilibrium.
7.
Write an equilibrium expression for the esterification reaction.
8.
Calculate the equilibrium constant for the esterification.
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