SUNCOI
Stellenbosch University Chemistry Outreach Initiative
in collaboration with the WCED1
FORMAL ASSESSMENT: TASK 1
Experiment: Preparation of esters
Learner Hand-out
[1]
MZ Moerat, Subject Advisor Physical Sciences, Western Cape Education Department, mmoerat@pgwc.gov.za
GRADE 12 ……
PHYSICAL SCIENCES
LEARNER: ………………………………………
TOTAL:
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FORMAL ASSESSMENT: TASK 1: Experiment: Preparation of esters
An ester is an organic compound that is formed when a carboxylic acid reacts with an
alcohol. In addition to an ester being formed, water is another product of the reactions.
Esterification typically requires a catalyst to speed up the reaction. For years concentrated
sulphuric acid (H2SO4) has been used to do so.
When carboxylic acids are esterified (combined with an alcohol to form an ester), some of the
resulting esters are liquids with fruity scents or flavours. These synthetic esters produced in
the laboratory are nearly the same molecules that give fruits their characteristic flavours.
SAFETY ALERT:
1. Sulphuric acid is a very dangerous chemical, which can cause severe chemical burns
when in contact with all human tissues. Remember to use concentrated sulphuric acid
with care and wash off any contacted area with cool water.
2. Alcohols and organic acids are flammable and should be kept away from open flames.
Do not overheat the reaction mixture. It must not boil. Use a cotton wool plug to
prevent alcohol from spilling and heat the test tube containing the solution by using a
water bath. Keep the test tube vertical in the water bath.
3. Methanol is toxic and could be fatal if swallowed.
4. All chemicals are hazardous. Wear safety goggles and gloves when handling
chemicals
5. Ensure that all gas taps are closed before and after the use of Bunsen burner(s).
6. Do not place your nose directly over the test tube to smell the ester produced while
the water bath is being heated.
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Aim
Synthesis of the following esters and identification of the smell:
A. Methyl salicylate
B. Propyl ethanoate
C. Pentyl ethanoate
D. Methyl butanoate
Match the odour of each ester to one of the following:
Banana, Pear, Apple, Oil of wintergreen/menthol
PLANNING: [10 marks]
Study the method provided and make a list of all the chemicals needed for the experiments.
Draw a labelled sketch to indicate how you will set-up the apparatus for the experiment.
Chemicals:
…………………………………………………………………………………………….
……………………………………………………………………………………...........
(3)
Labelled sketch of apparatus:
(4)
3
Identify the variables for this experiment
………………………………………………………………………………
………………………………………………………………………………
………………………………………………………………………………
(3)
METHOD: [0 Marks]
Part A:
Methyl salicylate (Methyl 2-hydroxybenzoate) is an ester in which the carboxyl group of
salicylic acid has reacted with the alcohol group of methanol (methyl alcohol).
O
O
OH
OH
+
O
CH3
OH
H3C
OH
+
H2O
1. Place 0.2 grams of salicylic acid into a clean, dry 10 ml test tube.
2. Add 6 drops of methanol and swirl the tube until the contents are well mixed.
3. Then add 1 drop of concentrated sulphuric acid.
4. Mix the tube contents and place the tube in a beaker of boiling water for three minutes.
5. After heating is complete remove the tube from the bath and add 15 drops of water to the
tube contents.
6. Cautiously note the door of the products in the test tube by wafting the scent to your nose.
Do this until you can detect an odour. Record the odour.
Part B:
1. Place 6 drops on propan-1-ol in a clean, dry 10 ml test tube.
2. Add 2 drops of ethanoic acid.
3. Add 1 drop of concentrated sulphuric acid, mix the contents and place the test tube in
a boiling water bath for 3 minutes.
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4. When heating is completed, remove the test tube from the bath, and add 20 drops of water
to the test tube contents and mix.
5. Cautiously note the odour of the products in the test tube by wafting the scent to your nose.
Do this until you can detect an odour. Record the odour.
Part C:
1. Place 6 drops on pentan-1-ol in a clean, dry 10 ml test tube.
2. Add 2 drops of ethanoic acid.
3. Add 1 drop of concentrated sulphuric acid, mix the contents and place the test tube in
boiling water bath for 3 minutes.
4. When heating is completed, remove the test tube from the bath, and add 20 drops of water
to the test tube contents. Swirl to mix.
5. Cautiously note the odour of the products in the test tube by wafting the scent to your nose.
Do this until you can detect an odour. Record the odour.
Part D:
1. Place 6 drops of methanol in a clean, dry 10 ml test tube.
2. Wearing chemically resistant gloves to avoid contact with skin, add 2 drops of butanoic
acid.
3. Add 1 drop of concentrated sulphuric acid, mix the contents and place the test tube in
boiling water bath for 3 minutes.
4. When heating is completed, remove the test tube from the bath, and add 20 drops of water
to the test tube contents and mix.
5. Cautiously note the odour of the products in the test tube by wafting the scent to your nose.
Do this until you can detect an odour. Record the odour.
5
RESULTS: [15 marks]
Record your results in a table.
Include the following columns: Names of the alcohol and carboxylic acid used,
name of the ester formed, as well as the smell of the ester.
(6)
Write balanced STRUCTURAL chemical equations for each of the reactions in:
Part B - ……………………………………………………………………………………… (3)
Part C - ……………………………………………………………………………………… (3)
6
Write a balanced CONDENSED STRUCTURAL chemical equation for the reaction in:
Part D - ……………………………………………………………………………………….. (3)
CONCLUSION/EXPLANATIONS: [10 marks]
1. Explain the purpose of the water bath.
…………………………………………………………………………………………………
…………………………………………………………………………….……………….. (2)
2. You added 20 drops of water to each mixture before smelling the ester. Explain how
this step enhances the smell of the ester by referring to the solubility of the reagents
and products in water.
…………………………………………………………………………………………………
………………………………………………………………………………………………. (2)
3. Explain why it is possible for the reaction mixture to boil over when placed in the water
bath when the water is not yet boiling.
……………………………………………………………………………………………. (1)
4. What is the purpose of the sulphuric acid in the reaction?
………………………………………………………………………………………………. (1)
5. Write down one safety precautions for this experiment.
…………………………………………………………………………………………….. (1)
6. Write down the name for the process of making an ester.
……………………………………………………………………………………………. (1)
7. Name any two uses of esters.
…………………………………………………………………………………………… (2)
TOTAL: 35 MARKS
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THIS MARKING MEMORANDUM WILL BE USED TO ASSESS THIS EXPERIMENT
PLANNING [10 marks]
Listing chemicals:
All alcohols correct
All carboxylic acids correct
Catalyst correct
(1)
(1)
(1)
Drawing apparatus:
All the apparatus is drawn correctly in the set-up
(1)
6 Appropriate labels indicated correctly
(3)
Identification of variables
1
Mark for each correct variable.
(3)
RESULTS [15 marks]
Table (One table summarizing all the results):
Table heading is appropriate
(1)
Column headings are appropriate
(2)
Data is appropriate, accurate and correct
(3)
Balanced chemical equation for each reaction:
Three marks for each correctly balanced equation.
(9)
CONCLUSIONS/EXPLANATIONS: [5 marks]
Scientific correct answers
(10)
TOTAL MARK
8
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