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Transcript
MODULE 2
17
WORKSHEET
ESTERS
Syllabus reference 9.3.5
Complete the following table.
FUNCTIONAL
GROUP
GENERAL
FORMULA
INTERMOLECULAR FORCES
—OH
CnH2n1OH
Hydrogen
bonding
COOH
CnH2n1COOH
Hydrogen
bonding
Alcohols
Esters
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—C
RC—OOR
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==
Alkanoic
acid
—
Dispersion
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soluble
Ethanol
C2H5OH
soluble
high
Ethanoic acid
CH3COOH
low
Methyl
ethanoate
insoluble
CH3—C
O
O— CH3
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pentanoic acid
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Copyright © 2007 McGraw-Hill Australia
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�� CONQUERINGCHEMISTRY HSC MODULE 2 WS 17
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EXAMPLE
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c
3-hexanol
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SOLUBILITY IN
WATER
—
O—C
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MELTING/
BOILING
POINTS
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SERIES
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methyl butanoate
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3
Name the following compounds:
a CH3CH2CH2CH2OH
1-butanol
b
CH3CHCH2CH2CH2CH3

OH
2-hexanol
c
CH3CH2COOH
propanoic acid
d
CH3CH2CH2CH2COOH
pentanoic acid
e
CH3CH2CH2C—O—CH2CH3

O
ethyl butanoate
f
CH3CH2CH2CH2C—O—CH3

O
methyl pentanoate
4
Explain why alcohols and alkanoic acids are soluble in water and esters (except for very simple
ones) are not.
Alcohols and alkanoic acid have hydrogen bonding but esters have only dispersion forces.
Copyright © 2007 McGraw-Hill Australia
CONQUERINGCHEMISTRY HSC
MODULE 2 WS 17
5
A student was given three containers labelled A, B and C. The student was told they were
pentanoic acid, hexane and 1-pentanol but not necessarily in that order. The student tested
the boiling point and found the following:
Boiling point
138ºC
69ºC
186ºC
Container
A
C
B
Based on the information provided suggest what was the liquid in the containers,
A, B and C. Give reasons for your decisions.
strong H bonding
B pentanoic acid
strongest bonding (Hydrogen bonding)
C hexane
weak bonding (dispersion)
Write balanced equations for the following reactions and name the products of the reaction:
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1-butanol reacting with ethanoic acid
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6
A 1-pentanol
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b
1-propanol reacting with butanoic acid
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8
Three compounds are known to be 1-propanol, ethanoic acid and methyl methanoate. Their
boiling points (but not in that order) are 118°C, 32°C and 97°C. Match the correct boiling point
to the compound giving reasons for your choice.
ethanoic acid
118oC
strongest bonding
1-propanol
97oC
strong bonding
methylmethanoate
32oC
weak bonding
Describe the process of refluxing and explain why it is necessary for successful esterification.
Refluxing is heating a reaction mixture in a vessel with a cooling condenser attached, in order to
prevent loss of any volatile production reactant. The reaction mixture needs to be heated to speed
up the reaction and refluxing is used to prevent loss of alcohol reactant.
Copyright © 2007 McGraw-Hill Australia
CONQUERINGCHEMISTRY HSC
MODULE 2 WS 17
9
Give two reasons why sulfuric acid is used during esterification refluxing.
1 It is used as a catalyst to speed up the reaction.
2 It absorbs the water that is produced and so forces equilibrium to the right.
10 a
Plot the boiling point against number of carbon atoms in the molecule for the esters in the table
below. Draw a straight line ruled between the points.
ESTER
BOILING POINT (°C)
ESTER
BOILING POINT (°C)
methyl methanoate
32 2
butyl ethanoate
126
6
methyl ethanoate
57 3
ethyl butanoate
121
6
methyl propanoate
80 4
ethyl methanoate
54
3
ethyl ethanoate
77 4
ethyl propanoate
99
5
propyl ethanoate
102 5
pentyl ethanoate
148
7
160
140
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100
80
60
40
20
0
1
2
3
4
5
6
7
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b
Use your graph to deduce the way that boiling point depends upon number of carbon atoms in
the molecule for esters.
The greater number of carbon atoms, the higher the boiling point.
c
For esters having the same number of carbon atoms in the molecule, does boiling point depend
significantly upon the number of carbon atoms in the alkyl group (as opposed to the number in
the acyl group—that is, in the ‘anoate’ part of the molecule)? Justify your answer.
For esters with the same total number of carbons, where there is more carbons in the alkyl
group, the boiling point is higher, e.g. butyl ethanoate > ethyl butanoate.
Copyright © 2007 McGraw-Hill Australia
CONQUERINGCHEMISTRY HSC
MODULE 2 WS 17
11 A student wanted to prepare the insoluble ester, butyl methanoate.
a What reagents would the student need to prepare this ester?
1-butanol, methanoic acid and sulfuric acid catalyst
b
The student used the following experimental set-up. Label the arrowed pieces of equipment.
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cooling water out
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cooling water in
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reaction mixture
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c
Describe how the student would extract the ester from the reaction mixture.
After heating, pour the contents of the flask into a separating funnel containing 10−15 ml
water. Stopper and shake funnel, allow layers to separate and discard aqueous layer.
Add solution of 1 mol/L Na2CO3. Shake, drain and discard lower layer,
leaving the ester in the funnel.
12 Complete the following table.
MAIN ESTER PRESENT
FLAVOUR
Methyl butanoate
apple
Octyl ethanoate
orange
Ethyl methanoate
grape
Butyl ethanoate
raspberry
13 Describe the occurrence, production and use of one ester.
Ethyl ethanoate is used as a solvent, and is manufactured on a large scale from acetic acid and
ethanol.
Copyright © 2007 McGraw-Hill Australia
CONQUERINGCHEMISTRY HSC
MODULE 2 WS 17