Brown's GCSE/IGCSE/O Level KS4 science–CHEMISTRY Revision Notes
Oil, useful products, environmental problems, introduction to
10. Carboxylic acids and esters
Carboxylic acids are a group of
organic compounds which have weakly acidic properties. The react with
bases/alkalis to for salts and release carbon dioxide from carbonates.
What are esters? What are esters used for? What connects the chemists laboratory
and the perfume industry! Carboxylic acids
react with alcohols to form organic
compounds called esters which are used as solvents and components in perfumes
and food flavourings.
Index of KS4 Science GCSE/IGCSE
Chemistry Oil & Organic Chemistry Pages: 1.
Fossil Fuels : 2. Fractional distillation of crude oil & uses of fractions : 3.
ALKANES – saturated hydrocarbons and combustion : 4.
Pollution, carbon monoxide, nitrogen oxides, what
makes a good fuel?, climate change–global warming :
5. Alkenes – unsaturated hydrocarbons :
6. Cracking – a problem of supply and demand, other products :
7. Polymers, plastics, uses and problems :
8. Introduction to Organic Chemistry – Why so many series of
organic compounds? : 9. Alcohols – Ethanol
– properties, reactions, biofuels :
10. Carboxylic acids and esters : 11. Condensation polymers, Nylon & Terylene,
comparing thermoplastics, fibres and thermosets
12. Natural Molecules – carbohydrates – sugars
– starch : 13. Amino acids, proteins,
enzymes & chromatography : 14. Oils, fats,
margarine and soaps :
15. Vitamins, drugs–analgesic medicines & food
additives and aspects of cooking chemistry! : 16. Ozone, CFC's and free
radicals : 17. Extra notes, ideas and links on
Global Warming and Climate Change : Multiple Choice and Gap–Fill Quizzes:
m/c QUIZ on Oil Products (GCSE/IGCSE easier–foundation–level)
m/c QUIZ on Oil Products (GCSE/IGCSE harder–higher–level) :
IGCSE/GCSE m/c QUIZ on other Aspects of Organic Chemistry
3 Easy linked GCSE/IGCSE Oil Products word–fill worksheets
CARBOXYLIC ACIDS and ESTERS
– other families of organic compounds
We find members of the homologous series called
carboxylic acids in fruits and in vinegar and many
in fragrances and food additives as carboxylic acid derivatives called esters.
The molecular structure and uses of carboxylic acids
form another homologous series
and have the functional group –COOH.
structures of the first three members are given below.
- The last alcohol structure given below is
the full displayed formula which you should definitely know, but you
also need to know the various abbreviated ways of writing the molecular
structure of alcohols.
- Names end in
...oic acid (actually here they all end in ..anoic acid).
contains ethanoic acid (old name 'acetic acid')
- Ethanoic acid can be manufactured on a large
scale by oxidising the alcohol ethanol.
in section 9 Oxidation
of the alcohol ethanol
- It is used as a
food preservative and in food flavourings.
- It is the oxidation of ethanol to ethanoic
acid that results in alcoholic drinks
turning sour (e.g. cider, wine) when exposed to air.
- The fruit material
already contains the enzymes that catalyse the oxidation of ethanol
('alcohol') in the presence of air.
- ethanol + oxygen ==> ethanoic acid +
- CH3CH2OH + O2
==> CH3COOH + H2O
+ O2 ==>
acid is used in the manufacture of the fibre, acetate rayon.
fruits like oranges and lemons and many soft drinks contain the
tri–carboxylic acid citric acid. and
contribute to the 'tarter' or 'sour' taste of fruit. The molecule contains
three acidic carboxylic acid groups –COOH.
- Citric acid is a natural
preservative (E330 on food labels) and is found in the largest
quantities in oranges, lemons, limes and grapefruit. It is an anti–oxidant.
Metal salts from citric acid, i.e. citrates, are used in dietary
supplements to deliver trace metal minerals in a biologically
available/absorbable chemical form.
- Citric acid can be
used in baking powder to react with sodium bicarbonate giving the raising
action from carbon dioxide gas formation. The same combination can be used
to give the fizzy drink effect in medicines like ant–acid stomach
- Citric acid is made in large
quantities for the food industry, including fizzy drinks - which can
be quite acid - dental concerns about the health of teeth here!
- Citric acid is strong enough to be
used in some limescale removers - so think about your teeth when
consuming all those fizzy drinks we might like!
- Aspirin is a carboxylic acid. Aspirin is a
drug used for pain relief and is taken regularly by those at risk from
heart attacks (see also
- Ascorbic acid (vitamin C) is another carboxylic
acid and is present in fresh fruit and vegetables
and is vital for good health AND the body cannot synthesise it, so you
must eat fruit and vegetables regularly!
- A lack of vitamin C can cause the
disease scurvy. The symptoms of scurvy are skin sores, spongy gums
and bleeding from mucous membranes. This is one example of malnutrition
diseases caused by a vitamin deficiency in a diet.
- Long chain carboxylic acids, known as 'fatty
acids', are used to make soaps and detergents.
- Below are some diagrams of the organic molecules or ions involved
- Diagram S1: The stearic acid molecule
or CH3(CH2)16COOH is a typical
long chain fatty acid obtained from naturally occurring plant oils and used
to make traditional soaps.
- Diagram S2: The salt sodium stearate C17H35COO–Na+,
formed when stearic acid is neutralised with sodium hydroxide is a
typical soap molecule.
- Carboxylic acids are weak acids, typically
solutions are around pH 2 to 6 (yellow–orange–pink with universal indicator).
They are called weak acids because only a
few % of the molecules in aqueous ionise to release protons (hydrogen
- It is the presence of hydrogen ions that
makes aqueous solutions of carboxylic acids acid.
- e.g. for ethanoic acid (vinegar)
- 98% CH3COOH(aq)
- This is a reversible reaction
with only 2% of the weak acid ionised on the right-hand side of the
Carboxylic acids react
with metals and are
neutralised by bases
(insoluble or soluble – alkalis and carbonates) to form salts ... with examples
of neutralisation ...
- metals react to form salts and
- ethanoic acid + magnesium ==>
magnesium ethanoate + hydrogen
- 2CH3COOH + Mg ==>
(CH3COO)2Mg + H2
- alkalis (soluble bases)
react to form a carboxylic acid salt
and water e.g.
- ethanoic acid + sodium hydroxide
==> sodium ethanoate + water
- CH3COOH + NaOH ==>
- ethanoic acid + potassium hydroxide
==> potassium ethanoate + water
- CH3COOH + KOH ==>
- insoluble bases dissolve
and react to form
salt and water e.g.
- zinc oxide + ethanoic acid ==>
zinc ethanoate + water
- ZnO + 2CH3COOH ==>
(CH3COO)2Zn + H2O
- carbonate and hydrogencarbonate
to produce a carboxylic acid salt, water and carbon dioxide e.g.
- ethanoic acid + sodium hydrogen
carbonate ==> sodium ethanoate + water + carbon dioxide
- CH3COOH + NaHCO3
==> CH3COONa + H2O + CO2
- ethanoic acid + sodium carbonate
==> sodium ethanoate + water + carbon dioxide
- 2CH3COOH +
Na2CO3 ==> 2CH3COONa
+ H2O + CO2
- propanoic acid + sodium carbonate
==> sodium propanoate + water + carbon dioxide
- 2CH3CH2COOH +
Na2CO3 ==> 2CH3CH2COONa
+ H2O + CO2
- aqueous ammonia solution
forms ammonium salts e.g.
- methanoic acid + ammonia ==>
- ethanoic acid + ammonia ==>
- CH3COOH + NH3
- Strictly speaking, ammonium
hydroxide doesn't really exist, but in older texts you will find these
reactions written in this way, but NOT correct e.g.
- propanoic acid + ammonium
hydroxide ==> ammonium propanoate + water
- CH3CH2COOH + NH4OH
==> CH3CH2COONH4 + H2O
Carboxylic acids are used to manufacture esters.
- Carboxylic acids react with alcohols
members of another homologous series called esters. Concentrated
sulphuric acid acts as a catalyst in this reaction.
- General word equation: carboxylic acid + alcohol ==>
ester + water
- ethanoic acid + ethanol
ethyl ethanoate + water
- sometimes more simply written as
- CH3COOH + CH3CH2OH
CH3COOCH2CH3 + H2O
- Structures of other esters
made from ethanoic acid:
methyl ethanoate using
ethanoate from using propanol (propan–1–ol, n–propyl alcohol).
- The first part of an ester's name is
derived from the alcohol e.g. methyl from methanol, ethyl from ethanol
and propyl from propanol etc. The second part of the name comes from the
carboxylic acid and ends in ...oate e.g. methanoate from methanoic acid,
ethanoate from ethanoic acid and propanoate from propanoic acid etc.
- The procedure for preparing
an ester are illustrated in the diagram below.
- This technique is called 'heating
under reflux', and ensures the reaction occurs the fastest at
highest possible reaction temperature, the boiling point of the mixture.
However, to prevent vapour loss by boiling/evaporation, the vapourised
liquids are condensed back into the reaction flask.
- The diagram shows a bunsen
burner being used to supply the heat ('my days'), these days its more
likely, and safer, to use an electrical heater that the round bottomed
flask fits in snugly.
- The colourless ester liquid is
separated and purified from the reaction mixture by fractional
distillation which is fully explained on the
Elements, Compounds, Mixtures
Notes (the example described is separating an ethanol/alcohol
mixture, but the same principal applies in separating the ester from the
water, unreacted alcohol and acid and the sulphuric acid catalyst.
- You can make butyl ethanoate by
- ethanoic acid +
butan–1–ol ==> butyl ethanoate + water
- Its an equilibrium, and
starting with the pure acid plus pure alcohol, you heat the mixture in
and you get about 2/3rds
conversion* to the ester, and the preparation reaction is
catalysed by a
few drops of concentrated sulphuric acid.
This means a theoretical maximum reaction
yield of about 67%.
- For more on % yields and 'atom
Calculations section 14.
- If the ester is warmed with
water or any dilute acid (faster), it changes back into the original
acid and alcohol. This reverse reaction is called hydrolysis i.e.
- ethyl ethanoate + water
==> ethanoic acid + ethanol
- whereas esterification is
- ethanoic acid + ethanol
ethyl ethanoate + water
- Esters are usually sweet/pleasant
smelling colourless liquids and occur widely–naturally in plants.
- Esters occur widely in
nature and are usually sweet/pleasant smelling liquids and widely used as fragrances
(components in perfumes) and
substances are used in many cosmetics but many mixtures contain
synthetic organic compounds.
- Many esters have sweet or fruity smells and
the colourless liquids are quite volatile, that's why fruits have strong
pleasant odours or aromas.
- Because they are volatile makes them ideal
for perfumes and fragrances in general.
- Because fruit sources are limited, many
esters are now synthesised in large quantities so the flavourings and
derived taste and aromas in fruit drinks, sweets and cakes etc. may be from
manufactured esters simulating strawberry, pineapple, pear, apple, grape,
orange, banana when used as food and drink additives etc.
- Esters are used in pharmaceutical and
household products e.g. ointments, washing-up liquids to give the
medications or cleaning products a pleasant odour.
- Examples of plant ester sources:
- Lavender oil essence is distilled
from the lavender plant
- Examples of flavouring esters:
- Pear drop sweet essence is an ester.
- Factors affecting perfume
design e.g. using esters:
- Designing a perfume – several issues
to address by way of design factors.
- The perfume needs to be a mixture of
compounds to give a prolonged perfumery effect.
- The perfumer chemist has to design the
mixture to give a particular fragrance which includes ...
- the top note – the first fragrant
molecule to be released,
- and the low note, the last molecule to be
- Esters are used as solvents e.g. nail
varnish remover, but also in paints, glues and ink formulations.
- They aren't totally free of health issues
but esters have replaced more harmful aromatic hydrocarbon solvents like
benzene (a carcinogen - a cancer promoting chemical) and methylbenzene (old
name toluene, also carcinogenic) in paint and varnishing products.
- BUT take care ...
- (i) although imparting a pleasant odour,
ester fumes can irritate mucous membranes in the nose and mouth,
- (ii) because they are volatile and
combustible, the fumes are highly flammable and easily ignited by a
naked flame. The vapour is heavier than air and will not disperse quickly,
- (iii) some people may be allergic to ester
fumes, or indeed their use as food additives.
Multiple Choice Quizzes and Worksheets
KS4 Science GCSE/IGCSE m/c QUIZ on Oil Products
KS4 Science GCSE/IGCSE m/c QUIZ on Oil Products
KS4 Science GCSE/IGCSE m/c QUIZ on other aspects of Organic Chemistry
3 linked easy Oil Products gap–fill quiz worksheets
ALSO gap–fill ('word–fill') exercises
originally written for ...
... AQA GCSE Science
Useful products from
crude oil AND
... OCR 21st C GCSE Science
Worksheet gap–fill C1.1c Air
pollutants etc ...
... Edexcel 360 GCSE Science
Crude Oil and its Fractional distillation
... each set are interlinked,
so clicking on one of the above leads to a sequence of several quizzes
Level Organic Chemistry revision notes
keywords equations: CH3COOH +
CH3CH2OH ==> CH3COOCH2CH3 + H2O * CH3CH2OH + O2 ==> CH3COOH + H2O * 2C2H5OH +
2Na ==> 2C2H5ONa + H2 * CH3CH2OH ===> CH2=CH2 + H2O *
Notes information to help revise
KS4 Science Additional Science Triple Award Separate Sciences Chemistry revision
notes for GCSE/IGCSE/O level Chemistry Revision–Information Study Notes for
revising AQA GCSE Science AQA GCSE Chemistry, Edexcel
GCSE Science, Edexcel GCSE Chemistry, OCR 21st Century Science Chemistry, OCR Gateway Science
GCSE science–chemistry CCEA/CEA GCSE science–chemistry
(and courses equal to US grades 8, 9, 10)
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