PDF file: Higher Chemistry: Making Esters - Education Scotland

HIGHER
CHEMISTRY
INTRODUCTION
- Making Esters-
One way of preparing esters is to condense an alcohol with a carboxylic acid:
O
O
C R'
R O H + H O
R O
C R'
+ H 2 O
UNIT 2
PPA 2
alcohol carboxylic acid ester
The reaction is slow at room temperature and the yield of ester is low. The rate can be increased by heating the
reaction mixture and by using concentrated sulphuric acid as a catalyst. The presence of the concentrated sulphuric
acid also increases the yield of ester.
The aim of this experiment is to prepare an ester and to identify some of the characteristic properties of esters.
Requirements
test tube and rack samples of alcohols (methanol, ethanol, propan-1-ol,
test tube holder butan-1-ol and pentan-1-ol)
paper towel samples of carboxylic acids (methanoic acid, ethanoic
rubber band acid, propanoic acid, benzoic acid and salicylic acid)
large beaker concentrated sulphuric acid
small beaker 1 mol l -1 sodium hydrogencarbonate
tripod
Bunsen burner and heating mat
cotton wool
Hazards
Concentrated sulphuric acid causes severe burns to the eyes and skin.
Methanol, ethanol and propan-1-ol are highly flammable and butan-1-ol and pentan-1-ol are
flammable.
All the alcohols are harmful by inhalation, skin absorption and by swallowing. Methanol is toxic.
The eyes may be damaged by alcohol splashes.
Methanoic, ethanoic and propanoic acids are corrosive and the benzoic and salicylic acids are
irritating to the eyes and skin.
Care
Wear goggles and immediately wash off any chemical spillages on the skin.
Wear gloves when working with the concentrated sulphuric acid.
When smelling the ester product do it very cautiously using the technique described below.
Procedure
Decide which ester you are to make and follow the procedure outlined below.
1. Before collecting the alcohol and carboxylic acid set up a water bath using the larger beaker and
heat the water until it boils. Turn off the Bunsen.
Alternatively, boil some water in a kettle and pour it into the large beaker.
2. Add the alcohol to a test tube to a depth of about 1 cm. To this add about the same volume of
carboxylic acid. If the acid is a solid then use a spatulaful.
3. In the interests of safety your teacher/lecturer may carry out the next step.
Add about 5 drops of concentrated sulphuric acid to the reaction mixture.

HIGHER
CHEMISTRY
- Making Esters-
UNIT 2
PPA 2
4. Soak the paper towel in cold water, fold it up and wrap it round the neck of the test tube.
Secure it with a rubber band. This arrangement acts as a condenser when the reaction mixture
is being heated.
5. Place a loose plug of cotton wool in the mouth of the test tube. This will contain any
chemicals which may spurt out of the reaction mixture when it is heated.
6. Place the test tube in the hot water bath.
7. While the reaction mixture is being heated add about 20 cm 3 of sodium hydrogencarbonate
solution to the small beaker.
8. After about 10 minutes, take the test tube from the water bath and remove the plug of cotton
wool. Slowly pour the reaction mixture into the sodium hydrogencarbonate solution. This
neutralises the sulphuric acid and any remaining carboxylic acid and so removes the smell of
the carboxylic acid.
9. Gently swirl the contents of the beaker and look to see if there is any sign of the ester
separating from the aqueous mixture.
10. To smell the ester follow the technique outlined below.
First breathe in deeply to fill the lungs with uncontaminated air.
With your nose at least 30 cm from the mouth of the beaker gently waft the vapour towards
your nose and take just a sniff.

HIGHER
CHEMISTRY
Name:
Date:
- Making Esters-
- ASSESSMENT SHEET -
* State the aim of the experiment naming the ester you made.
PC(b)
Procedure
* Draw a labelled diagram of the assembled apparatus used to prepare an ester.
PC(b)
* How was the reaction rate increased?
PC(b)
PC(a) PC(b) PC(c) PC(d) PC(e)
* What was the function of the 'wet paper towel' condenser?
PC(b)
Results
* State two pieces of evidence which suggested that an ester had been formed.
PC(c)
Teacher’s/Lecturer’s
Initials
UNIT 2
PPA 2

HIGHER
CHEMISTRY
- Making Esters-
Conclusion
* Using full structural formulae, write an equation for the condensation reaction you
carried out and name the ester formed.
PC(e)
UNIT 2
PPA 2

HIGHER
CHEMISTRY
- Making Esters-
- TEACHER/LECTURER/TECHNICIAN SHEET -
Requirements per student (or group)
Reagents
selection of alcohols (~ 1 cm 3 )
(methanol, ethanol, propan-1-ol, butan-1-ol
and pentan-1-ol)
selection of carboxylic acids (~ 1 cm 3 or 1 spatulaful)
(methanoic acid, ethanoic acid, propanoic acid,
benzoic acid and salicylic acid)
CONCENTRATED SULPHURIC ACID (A FEW
DROPS)
1.0 mol l -1 sodium hydrogencarbonate (~ 20 cm 3 )
(84.0 g sodium hydrogencarbonate per litre)
methanol
ethanol
propan-1-ol
butan-1-ol
pentan-1-ol
ethanoic acid
methanoic
acid
propanoic
acid
benzoic acid
salicylic acid
toxic
UNIT 2
PPA 2
highly
flammable
highly
flammable
harmful flammable
corrosi
ve
concentrated sulphuric
acid
APPARATUS
test tube (1) 100 cm 3 glass beaker (1)
test tube rack (1) tripod (1)
test tube holder (1)
Bunsen burner (1)
paper towel (1)
heating mat (1)
rubber band (1)
400 cm
cotton wool
3 glass beaker (1)
flammable
corrosive
harmful
corrosive

HIGHER
CHEMISTRY
Safety Measures
- Making Esters-
Preparation/provision of: Main Hazards Control Measures
methanol
ethanol
propan-1-ol
butan-1-ol
pentan-1-ol
methanoic acid
ethanoic acid
propanoic acid
benzoic acid
salicylic acid
All harmful to varying extent by
ingestion, inhalation and by skin
absorption.
Methanol is more toxic than the
others.
Methanol, ethanol and propan-1-ol
are highly flammable and the others
are flammable.
The three aliphatic acids are
corrosive.
Methanoic acid is quite toxic and
ethanoic acid is flammable.
The two aromatic acids are very
irritating to the skin.
concentrated sulphuric acid Causes severe burns to eyes and
skin.
Notes
This experiment should be carried out in a well-ventilated room.
UNIT 2
PPA 2
Wear eye protection and pvc gloves.
Ensure absence of ignition sources.
Dispense into small reagent bottles
(say 50 or 100 cm 3 ) in a wellventilated
room or preferably in a
fume cupboard.
Wear goggles and pvc gloves during
dispensing.
Ensure absence of ignition sources.
Wear goggles or faceshield and pvc
gloves.