Experiment P01
Determination of the equilibrium constant for esterification
(Ethanoic acid and Propan-1-ol)
Chemicals:
Glacial ethanoic acid, (density = 1.05 g cm-3, 17.5M), (10 cm3)
propan-1-ol, (density = 0.80 g cm-3, 13.33 M), (10 cm3)
conc. H2SO4, (1 cm3)
standard 0.50 M NaOH, (400 cm3)
phenolphthalein indicator,
ice.
Apparatus:
Apparatus for refluxing,
titration apparatus,
1.0 cm3 pipette. (1)
10.0 cm3 pipette(2)
Principle:
In the presence of conc. H2SO4 and under reflux, ethanoic acid undergoes a
reversible reaction with propan-1-ol to form ester and water. As equilibrium is
reached,
CH3COOH(l)+CH3CH2CH2OH(l)
Kc =
CH3COOCH2CH2CH3(l)+H2O(l)
[CH 3 COOCH 2 CH 2 CH 3 ]eq [ H 2 O]eq
[CH 3 COOH ]eq [CH 3 CH 2 CH 2 OH ]eq
By titrating the reaction mixture with standard alkali solution before and after
refluxing, the quantity of the acid used, and thus the quantities of the alcohol used
as well as of the ester and water formed can be determined.
Knowing the quantities or molar concentrations of the species present in the
equilibrium mixture, the equilibrium constant, Kc can be calculated.
P.1
Experiment P01
Determination of the equilibrium constant for esterification
(Ethanoic acid and Propan-1-ol)
Procedure:
a.
Measure accurately 10.0 cm3 of glacial ethanoic acid and 10.0 cm3 of propan-1-ol into
a clean, dry 100 cm3 distillation flask. Mix thoroughly.
b.
Transfer 1.00 cm3 of the mixture by pipette to a 125-conical flask containing about 25 cm3
distilled water and 2 drops of phenolphthalein indicator solution. Titrate to end point with
0.50 M NaOH. Record this volume. Repeat the titration to obtain an average volume of
0.50 M NaOH used.
(Find the original concentration of CH3COOH after mixing)
c.
Add 8 drops of conc. H2SO4 to (the remainder of) the acid-alcohol solution while
continuously swirling the flask. Titrate another 1.00 cm3 sample immediately. Record this
volume. The difference between this volume and the one in (b) above represents the volume
to be subtracted from subsequent titration to correct for the amount of H2SO4 present.
(Find the concentration of H2SO4)
d.
Add a few boiling chips to the flask, and attach it to a water-cooled reflux condenser.
Reflux for 1 hour (first refluxing process). Cool the flask and its contents in an ice bath.
Remove 1.00 cm3 sample from the flask for titration with the 0.50 M NaOH (as
procedure b). Record the volume needed (and correct it for the H2SO4).
(Find the concentration of the remaining CH3COOH)
e.
Continue refluxing (second refluxing process) for an additional 1/2 hour, cool and titrate
another 1.00 cm3 sample. The two titrations should agree to within 0.20 cm3. Otherwise,
repeat the second refluxing process.
(To ensure the esterification is complete)
f.
Use the data to calculate the equilibrium constant, Kc, of the esterification reaction.
P.2
Experiment P01
Determination of the equilibrium constant for esterification
Procedure b: (specimen result)
Titration
1(trial)
2
3
Final burette reading (cm3)
3.15
1.10
2.25
Initial burette reading (cm3)
23.20
20.95
22.20
Volume of NaOH used (cm3)
20.05
19.85
19.95
4
Average volume of NaOH used (Vb) = 19.90 cm3
--------------------------------------------------------------------------------------------------------------------Procedure c: (specimen result)
Titration
1(trial)
2
3
Final burette reading (cm3)
2.15
1.15
3.20
Initial burette reading (cm3)
24.20
22.90
24.85
Volume of NaOH used (cm3)
22.05
21.75
21.65
4
Average volume of NaOH used (Vc) = 21.70 cm3
--------------------------------------------------------------------------------------------------------------------Procedure d:
Titration
1(trial)
2
3
4
Final burette reading (cm3)
Initial burette reading (cm3)
Volume of NaOH used (cm3)
Average volume of NaOH used (Vd) =
--------------------------------------------------------------------------------------------------------------------Procedure e:
Titration
1(trial)
Final burette reading (cm3)
Initial burette reading (cm3)
Volume of NaOH used (cm3)
Average volume of NaOH used (Ve) =
N.B. If Vd = Ve, esterification is complete.
P.3
2
3
4
Experiment P01
Determination of the equilibrium constant for esterification
(Ethanoic acid and Propan-1-ol)
Name:
Partner 1
Seat No.:
Partner 2
Date:
Partner 3
Grade:
Given:
Concentration of NaOH =
Calculation:
Conc. of propan-1-ol before mixing = 13.33 mol/dm3
Conc. of ethanoic acid before mixing = 17.50 mol/dm3
13.33
Conc. of propan-1-ol after mixing =
= 6.665 (mol/dm3 )
2
17.50
Conc. of ethanoic acid after mixing =
= 8.75 (mol/dm3)
2
In procedure b, average vol. of NaOH used = 19.90 cm3
In procedure c, average vol. of NaOH used = 21.70 cm3
Vol. of NaOH required to neutralize conc.H2SO4 = 21.70 – 19.90 = 1.8 (cm3)
In procedure d (and procedure e), average vol. of NaOH used =
- 1.8 cm3
Vol. of NaOH required to neutralize ethanoic acid (at equil.) =
=
Let M be the concentration of CH3COOH at equil.
Then M ×
1
=
1000
×
M=
i.e. [CH3COOH]eq =
CH3COOH(l)+CH3CH2CH2OH(l)
At start
8.75
CH3COOCH2CH2CH3(l)+H2O(l)
6.665
0
At equil.
Conc. of CH3COOH consumed =
Conc. of propan-1-ol at equil. =
[CH3COOCH2CH2CH3]eq =
[H2O]eq =
Kc =
P.4
0