TASK 1 Experiment: Preparation of esters Teacher`s Memorandum

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SUNCOI
Stellenbosch University Chemistry Outreach Initiative
in collaboration with the WCED1
FORMAL ASSESSMENT: TASK 1
Experiment: Preparation of esters
Teacher’s Memorandum
[1]
MZ Moerat, Subject Advisor Physical Sciences, Western Cape Education Department, [email protected]
PLANNING [10 marks]
Listing chemicals:
All alcohols correct:
All carboxylic acids correct:
Catalyst correct:
Methanol, Propanol, Pentan-1-ol
Salicylic acid, ethanoic acid, butanoic acid
Concentrated Sulphuric acid/Conc. H2SO4
(1)
(1)
(1)
Drawing apparatus:
1/2 mark for each correct label:
1.
2.
3.
4.
5.
6.
Bunsen burner
tripod/gauze
alcohol/carboxylic acid/sulphuric acid
test tubes
beaker /water bath
thermometer
All the apparatus is drawn correctly in the set-up
(1)
6 Appropriate labels indicated correctly
(3)
Identification of variables
One mark for each correct variable:
Independent – Type of alcohol and carboxylic acid used.
Dependant - Smell/Type of ester prepared
Controlled - amount of reactants used/accept other applicable answers
(3)
RESULTS [15 marks]
Table (One table summarizing all the results):
Acid and Alcohol Reacted
Salicylic Acid and Methanol
Ester Product
Odour detected
Methyl 2-hydroxybenzoate Oil of wintergreen/menthol
Ethanoic acid and Propanol
Propyl ethanoate
Pear
Ethanoic acid and Pentanol
Pentyl ethanoate
Banana
Buthanoic acid and Methanol
Methyl butanoate
Apple
Table heading is appropriate
(1)
2
Column headings are appropriate
(2)
Data is appropriate, accurate and correct
(3)
Balanced chemical equation for each reaction (B to D):
PART B:
H O
H H H
H O
H H H
H
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H–C–C–O–H + H–O–C–C–C–H → H–C–C–O–C–C–C–H + O–H
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H
H H H
H
H H H
PART C:
H O
H H H H H
H O H H H H H
H
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H–C–C–O–H + H–O–C–C--C--C–C–H → H–C–C–O–C–C–C--C--C–H + O–H
|
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H
H H H H H
H
H H H H H
PART D:
CH3CH2CH2COOH
+ CH3OH →
CH3CH2CH2COOCH3
Three marks for each correctly balanced equation.
(9)
CONCLUSIONS/EXPLANATIONS: [10 marks]
1. The reactants are flammable. The water bath prevents direct contact with the flame
in the case of spillage.
(2)
2. The excess reagents (alcohol and carboxylic acid) will dissolve in water, while the
product (ester) does not.
(2)
3. The reactants have lower boiling points than water.
(1)
4. Catalyst
(1)
5. (Any one)
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Safety goggles
Lab coat
Gloves
Use well-ventilated room or in fume cupboard.
Wash off any contacted area immediately with large amounts of cold water.
Ethanoic acid is flammable, caustic and cause burns. Do not inhale.
Pentanol and ethanol is flammable, use a water bath.
Do not get in contact with the sulphuric acid.
Methanol is highly flammable and toxic if it is inhaled or swallowed.
6. Esterification
(1)
(1)
7. (Any One)
3
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Making perfumes
Making air fresheners
Making drinks
Making baking/ food colorants
Used by animals for hunting
Used to identify partners for mating
(1)
TOTAL MARK
/35/
TEACHER’S NOTES:

Order reagents and apparatus well in advance. (You may contact B & M Scientific, SigmaAldrich, Kimix, Merck and Lasec or any other supplier for the cheapest quote).
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Ensure that learners are well aware of the safety precautions for this experiment.

The reagents used in this task may be replaced with any other available alcohol or carboxylic
acid. The “Additional Esters Hand-out” contains four other possibilities which may be used as
replacements. (The preparation with butanoic acid leaves an unpleasant smell in the
classroom.)

Many esters have very similar smells. Choose esters with distinctive smells if possible.
(See attached list of esters).

Make use of IUPAC names as far as possible when setting the task. The current prescribed
text book uses some general names (e.g. acetic acid for ethanoic acid) in their practical, so
add these names to your memos.
4
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