CARBOXYLIC ACIDS –
chemistry & uses
See also 10b.
ESTERS – chemistry and uses
(now on a separate page)
Brown's GCSE/IGCSE/KS4 science–CHEMISTRY Revision Notes
Oil, useful products, environmental problems, introduction to
10a. Carboxylic Acids – structure, properties and uses
Carboxylic acids are a group of
organic compounds which have weakly acidic properties. Carboxylic acids react with
bases/alkalis to for salts and release carbon dioxide from carbonates. They
react with alcohols to form esters.
These revision notes on the uses and chemical properties of carboxylic acids should prove useful for the
NEW AQA GCSE chemistry,
Edexcel GCSE chemistry & OCR GCSE chemistry (Gateway & 21st Century) GCSE (9–1),
(9-5) & (5-1) science courses.
Index of KS4 Science GCSE/IGCSE/O Level
Chemistry Oil & Organic Chemistry revision notes pages: 1.
Fossil Fuels & carbon Cycle : 2.
Fractional distillation of crude oil & physical
properties and uses of fractions,
what makes a good fuel? : 3.
ALKANES - saturated hydrocarbons, structure, uses, combustion : 4.
Pollution, carbon monoxide, sulfur/nitrogen oxides, climate change-global warming,
carbon footprint :
5. Alkenes - unsaturated hydrocarbons,
structure and chemistry :
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? : 9a. Alcohols,
Ethanol, manufacture, physical properties & chemical reactions
Biofuels & alternative fuels,
hydrogen, biogas, biodiesel
: 10a. Carboxylic
acids - chemistry and uses
: 10b. Esters, chemistry and uses including perfumes
: 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
destruction, CFC's and free
radicals : 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
ALL my Advanced
Level Organic Chemistry revision notes
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
The full displayed formula for the
first five members of the homologous series of CARBOXYLIC ACIDS
diagrams show ALL the covalent bonds (C-H, C-C, C-O, C=O and O-H) in
carboxylic acid molecules
They can also be written as: HCOOH,
CH3COOH, CH3CH2COOH, CH3CH2CH2COOH
The molecular structure of carboxylic acids
Carboxylic acids form another homologous series
and have the functional group –COOH.
- A homologous series is a family of
compounds which have the same general formula and have a similar
molecular structure and similar chemical
properties because they have the same functional group of atoms (e.g.
in this case the carboxylic acid -COOH group).
- The homologous series of carboxylic acids
have the general formula CnH2n+1COOH,
where n = 0, 1, 2 etc. number of carbon atoms in the molecule minus 1.
- The functional group (COOH) is a
group atoms common to all members of a homologous series that confer a
particular set of characteristic chemical reactions on each member of the
series e.g. in this series they all behave like acids with alkalis,
carbonates etc., they all form compounds called esters when reacted with
- Members of a homologous series
have similar physical properties such as
appearance, melting/boiling points, solubility etc. BUT show trends in
them e.g. steady increase in melting/boiling point with increase in carbon
number or molecular mass.
- It is important to realise that members of a given
homologous series like carboxylic acids have similar chemical
reactions because their molecules contain the same functional group (COOH)
and so you can predict the chemical reactions and products of the
other members of the carboxylic series
structures of the first three members of the carboxylic acid homologous
series are shown 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),
- and check out their formula from the general formula above,
the final structure is the full displayed formula showing every covalent
bond in the molecule (C–H, C=O, C–O, O–H, C–C) and note the arrangement of
atoms in the COOH functional group, common to all the members of the
homologous series of carboxylic acids. The first three are as follows ...
- methanoic acid (old
name 'formic acid')
, 1st in the series
- ethanoic acid
(old name 'acetic acid', in vinegar)
- C2H5COOH or
, 2nd in the series
- propanoic acid
(old name 'propionic acid')
, 3rd in the series etc.
- ADVANCED A Level revision notes on the
structure and naming of CARBOXYLIC ACIDS and DERIVATIVES,
including nomenclature of isomers
(NOT needed for GCSE/IGCSE students!)
The properties and uses of carboxylic acids
- This particular homologous series of
carboxylic acids are colourless liquids with very strong odours (pungent
smell) and tastes.
- The obnoxious smell of rancid butter and
sweaty socks are due to the formation of carboxylic acids.
- It should be mentioned here that carboxylic
acids with long carbon chains are called fatty acids, because they are
combined with an alcohol called glycerol to form large ester molecules
make up most natural oils from plants and fat in animals.
- Many traditional soaps are made from natural
oils and fats.
- The fatty acids may be saturated (no C=C
double bonds) or unsaturated (with at least one C=C double bond) in the
- For more details on glycerides and soaps see
margarine and soaps
- Vinegar contains ethanoic acid (old name 'acetic acid')
- In the chemical industry 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 ====>
- This reaction occurs if wine, beer or cider
is left out open to the air, it eventually becomes vinegar and not very nice
to drink!, but vinegar is very nice in salad dressings and on your fish and
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,
originally derived from plant oils.
- Below are some diagrams of the organic molecules or ions involved,
typically with 16 to 20 carbon atoms in the chain.
- 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 weak acid
solutions have a pH of around 2 to 6 (yellow–orange–pink with universal indicator),
which is somewhat higher than strong acid solutions with a pH of 0 to 2.
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) around 98%
remains unionised i.e. as the original neutral molecule.
- Propanoic acid and butanoic acid are equally weak
- This is a reversible reaction
with only 2% of the weak acid ionised on the right–hand side of the equilibrium.
- At similar concentrations, strong
acids have a low pH of 0 or 1, because they are more fully ionised.
- Ethanoic acid will turn blue litmus pink
and universal indicator gives an orangey–red colour.
- Being a weak acid, the pH is higher than
in strong mineral acids like hydrochloric acid and the rate of reaction
is slowed down too.
- For a more detailed discussion of these points see
of acids and bases
- Despite being a weak acid, carboxylic
acids like ethanoic acid behave like any other acid and react with
metals, alkalis and carbonate to form salts and fizzing here and there!
Carboxylic acids react
with metals and are
neutralised by bases/alkalis
(insoluble or soluble metal oxides, hydroxides and carbonates) to form salts.
The salt names depends on the name of the acid, so aqueous solutions
of methanoic acid form
methanoate salts, ethanoic acid gives ethanoate salts, propanoic
acid gives propanoate salts and butanoic acid gives butanoate
salts on neutralisation. The salts can be crystallised from the
solution by evaporation.
- metals react and dissolve to form a salts and
- ethanoic acid + magnesium ==>
magnesium ethanoate + hydrogen
- 2CH3COOH + Mg ====> (CH3COO)2Mg + H2
- butanoic acid + zinc ====>
zinc butanoate + hydrogen
- 2CH3CH2CH2COOH +
Zn ====> (CH3CH2CH2COO)2Zn + H2
- Not on the syllabus, but an interesting
tragic story of 'old acetic acid' and lack of appreciation of
- Ethanoic acid very slowly reacts with lead to
form lead(II) ethanoate (old name lead acetate), once called 'sugar
- 2CH3COOH + Pb ====> (CH3COO)2Pb + H2
- The salt formed was called 'sugar of lead'
because it had a sweet taste!
- Cider makers in the past had dipped
rods of lead into cider to neutralise any acetic acid that had
formed and sweeten the beverage.
- Unfortunately, lead is one of many heavy
metals and that are highly toxic and lead compounds affect the brain
and nervous systems and can be fatal.
- Cases of lead poisoning have occurred through
millennia, including the Romans, by using lead pots in food
preparation or concentrating liquids.
- So, any cider left over that goes sour,
dispose of it or let turn completely into cider vinegar for the
- alkalis (soluble bases)
react to form a carboxylic acid salt
and water e.g.
- ethanoic acid + sodium hydroxide
==> sodium ethanoate + water
- CH3COOH + NaOH ====> CH3COONa
- ethanoic acid + potassium hydroxide
==> potassium ethanoate + water
- CH3COOH + KOH ====> CH3COOK
- propanoic acid + sodium hydroxide
==> sodium propanoate + water
- CH3CH2COOH + NaOH ====> CH3CH2COONa
- insoluble bases dissolve
and react to form
salt and water e.g.
- zinc oxide + ethanoic acid ====>
zinc ethanoate + water
- 2CH3COOH + ZnO ====> (CH3COO)2Zn + H2O
- ethanoic acid + calcium hydroxide ====>
calcium ethanoate + water
- 2CH3COOH + Ca(OH)2 ====> (CH3COO)2Ca
- ethanoic acid + magnesium hydroxide ====>
magnesium ethanoate + water
- 2CH3COOH + Mg(OH)2 ====> (CH3COO)2Mg
- butanoic acid + magnesium hydroxide ====> magnesium
butanoate + water
- 2CH3CH2CH2COOH + Mg(OH)2 ====>
(CH3CH2CH2COO)2Mg + 2H2O
- carbonate and hydrogencarbonate
produce a carboxylic acid salt, water and carbon dioxide gas 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
- ethanoic acid + magnesium carbonate
==> magnesium ethanoate + water + carbon dioxide
- 2CH3COOH + MgCO3 ====> (CH3COO)2Mg + H2O + CO2
- ethanoic acid + calcium carbonate
==> calcium ethanoate + water + carbon dioxide
- 2CH3COOH + CaCO3 ====> (CH3COO)2Ca + H2O + CO2
- aqueous ammonia solution
forms ammonium salts e.g.
- methanoic acid + ammonia ====>
- HCOOH + NH3
- 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
- A whole variety of esters can be made using an
alcohol + carboxylic acid + a strong acid catalyst.
notes on esters are on a separate page now, and they are a very
important group of compounds and more than merit their own page!
- AMINO ACIDS
- Amino acids have two functional groups.
- The carboxylic acid group -COOH and the
amino or amine group -NH2
- The simplest one is aminoethanoic acid (glycine)
- Amino acids can undergo condensation
polymerisation via the two functional groups to form peptides,
and all sorts of combinations of amino acids produce the huge variety of
proteins found in living systems.
- For glycine the condensation polymerisation to give a
glycine peptide can be shown as ..
- n H2N-CH2-COOH ====>
-(NH-CH2-COO-)n- + 2n H2O
- where n is a very large number, with the elimination
of 2n water molecules.
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
ALL my Advanced
Level Organic Chemistry revision notes
keywords equations: CH3CH2OH + O2 ==> CH3COOH + H2O
Revision notes on carboxylic acids
reactions uses KS4 Science
GCSE/IGCSE/O level Chemistry Information on carboxylic acids reactions uses for revising for AQA GCSE
Science, Edexcel Science chemistry IGCSE Chemistry notes on carboxylic acids
reactions uses OCR 21st Century
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carboxylic acids reactions uses CIE O Level chemistry CIE IGCSE chemistry notes on
carboxylic acids reactions uses CCEA/CEA gcse science
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chemistry courses revision guides explanation chemical equations for carboxylic
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