Oils, fats, margarine, soaps and detergents
Brown's GCSE/IGCSE/O Level KS4 science–CHEMISTRY Revision Notes
Oil, useful products, environmental problems, introduction to
14. 'Domestic' products – Oils, fats, margarine and soap organic molecules
This page describes the
molecular structure of natural oils, fats and 'soapy' soaps. How do you make
soaps from natural oils? How is margarine made? What is the composition of a
typical margarine? The terms–names glycerol, triglycerides, long chain fatty
acids, monounsaturates and polyunsaturates all explained. The uses of oils and
fats is described and explained. There are extra sections on dry cleaning
solvents and biological detergents. These revision notes on edible oil
extraction, use in cooking, fats, margarine production and the molecules we use
in soaps and detergents 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
Naturally Occurring Molecules from plants
Fats, Oils and Margarine
Natural vegetable oils and animal fats
are important raw materials for the chemical industry wide ranging applications and uses e.g. soaps, detergents, cosmetics,
lubricants, paints, many food industry products. It is possible that
in future vegetable oils could be an important renewable and
sustainable alternative to some of the products we derive from crude
Plant Oils – Uses
Many plants produce useful oils that can be
extracted and converted into consumer products
including processed foods.
Emulsions can be made and have a number of uses.
Vegetable oils can be hardened
to make margarine.
Biodiesel fuel can be produced from vegetable oils.
See biomass and alternative fuels
Vegetable oils are an important
source of energy and even vitamins like vitamin E in seed
Vegetable oils contain
essential fatty acids which are bodies need for certain metabolic
Plant Oils – extraction and
processing into useful products
The fruits and seeds of some
plants contain appreciable and economically viable quantities of oil.
eg olives (olive oil), peanuts, walnuts
brazil nuts, rape seed, avocados, soya oil etc.
They are usually liquid at room
temperature, whereas animal fats tend to be solids at room temperature.
The traditional way to extract
the oil from plant material is to crush it between metal plates of a
press, which literally squashes the oil out eg extracting olive oil from
You can also extract the oil
from crushed plant material by using a centrifuge (a high spin
'barrel' with holes in the out surface), whose rapid rotation spins the oil
out to out regions of the container from which the oil can be collected
through the outer holes.
It is also possible to extract
the plant oil with a solvent.
However, before any oil can be
used it must be purified to remove impurities.
Plant oils can be highly refined
by fractional distillation which removes any solvents, water and other
You can also use steam
distillation to extract lavender oil or orange oil etc. from the crushed
plant leaves or peel etc. but this more to do with the
perfume industry than the food
Oils and Fats
are an important way of storing chemical energy in living
systems and are also a source of essential long–chain fatty acids.
Plant oils and animal fats have
a high energy density (higher than carbohydrates) and be easily stored in
living organisms until they are needed to supply extra energy to power the
chemistry of life.
If we take in more calorific
food that we need e.g. excess carbohydrate or 'fatty food', then that excess
energy supply is converted to fat and stored for future use, but, if it
isn't used up, then obviously you will put on weight.
- Fats and oils are esters formed from
long chain fatty acids and the 'triol' alcohol glycerol
, which has three C–O–H groups.
- Glycerol is the alcohol plants and animals use to make
oils and fats which are esters we use in food and soaps.
- Animals and plants combine glycerol and long
chain fatty acids to make triglyceride esters – fats from animals and oils
Most of them are esters of
the tri–alcohol ('triol') glycerol (systematic name
propane–1,2,3–triol, but that can wait until AS–A2 level).
The carboxylic acids which
combine with the glycerol are described as 'long–chain fatty acids'.
The resulting ester is called a
'triester' or 'triglyceride' and they are the major components in animal
fat, vegetable oils, and processed fats like margarine etc..
The 'long–chain fatty acids'
can be saturated, with NO C=C double bonds, and so forming saturated oils
or fats (1st diagram below of the triglyceride formed from palmitic
The 'long–chain fatty acids'
can be unsaturated, with one or more C=C double bonds, and so forming
oils or fats (2nd diagram below of the triglyceride formed from oleic
If there is just one
C=C double bond in the fatty acid chain, it is known as a
monounsaturated oil or fat (upper diagram).
If there are at least
two C=C double bonds in the fatty acid chain it is called a
polyunsaturated oil or fat exemplified by the polyunsaturated fatty
acid chain, with three carbon = carbon double bonds of the unsaturation,
in the lower diagram.
Plant oils are mainly
unsaturated fats with one or more carbon = carbon double bonds in the
fatty acid chain and they are usually thick (viscous) liquid oils at
room temperature. That's why plant oils are hydrogenated, adding
hydrogen to the double bonds, to make them less unsaturated and raise
the melting point to produce spreads like margarine.
Some sub–notes on Oil and Fat Structure:
issues dealt with further down)
Most oils and fats have quite long
fatty acid chain molecules in their molecular structure, which can be ...
Saturated, with no
double carbon = carbon bonds, so no atoms can be added to the molecule,
in this context they are referred to as saturated fat molecules.
Unsaturated, with one
or more carbon = carbon double bonds in the three fatty acid parts of
the molecule. In this context these molecules are referred to as
monounsaturated or polyunsaturated vegetable oils.
Unsaturated oils will
decolourise bromine water, a simple test for unsaturation.
This is because bromine
atoms can add across the double bonds like any
Ignoring the rest of the
molecule, the reaction in the unsaturated part of the oil/fat molecule
Although much shorter than
polymer molecules, oils and fats have the same ester linkages as perfume
molecules and Terylene
plastic, but with different units,
food for thought!
They are not as big as polymer molecules, but a lot bigger than a single
petrol or a simple sugar molecule.
There can be 1 to 3 different saturated or
unsaturated fatty acid components, so lots of variation possible in structure
of the oil or fat.
Monounsaturated fats have one C=C
double bond in the fatty acid chains, polyunsaturated fats usually have at least
two C=C bonds in their molecular structure.
For the same molecular size in terms of
carbon number, unsaturated fats have slightly lower intermolecular
forces because the C=C double bond produces a kink in the carbon
chain and they can't pack as closely together as the saturated
However, this means these unsaturated
oils are not as conveniently 'spreadable' as 'butter'.
To overcome this problem, 'margarine'
was invented in which the runny vegetable oil is 'hardened'
by hydrogenation to produce a higher melting spreadable solid.
The melting point is
still low, but not to low to remain liquid at room temperature ie a margarine is a soft solid at room
temperature and doesn't go too hard in the refrigerator and spreads
So, large quantities
of vegetable oils are hydrogenated for the food industry to
convert them from runny oils into low melting soft solids that
spread on bread etc. easily.
The vegetable oils are reacted with
hydrogen gas at 60oC using
a nickel catalyst (Ni).
These are called
and have higher melting point than unsaturated vegetable
oils, so they are a low melting solid at room temperature rather than the sticky–syrupy vegetable oil you
might use is cooking and salad dressings.
This reaction adds hydrogen
atoms to the double bonds making a more saturated and more
'spreadable' higher melting soft solid fat that we call 'margarine'.
no double bond and unsaturated means double bond in this context.
The reaction for any
carbon = carbon double bond,
+ H2 == Ni ==> –CH2–CH2–
converting an unsaturated part of the molecule to a saturated
This type of reaction is
called hydrogenation – quite literally – addition of
represents the unsaturated part of the hydrocarbon chain parts
in the oil molecule.
While the margarine
is still liquid, the expensive nickel catalyst can be recovered
from the margarine by filtration and reused.
On cooling down the
solid margarine is formed, but still soft enough to spread
polyunsaturated vegetable oils are hydrogenated to make
The diagram above
illustrates in a simplified way the hydrogenation of a
monounsaturated fat (one double bond per fatty acid chain) to a
fully saturated flat. Note that one hydrogen molecule is added
to each double bond giving the balanced equation for
hydrogenating vegetable oils to margarine.
In the case of
margarine, made from polyunsaturated vegetable oil, the oil is
only partially hydrogenated, thus reducing the number of C=C
double bonds in the molecule, BUT not making a saturated fat and
still raising the melting point above room temperature. If it
was completely saturated it would be too hard to spread.
BUT it does mean that it is
more like animal fat now but various blendes have been developed to
suit your dietary needs or desires!
The hydrogenated oils
are used as spreads and general baking like cakes, bread and
Technically, margarine is only partially hydrogenated because fully saturated
fats would be too hard and difficult to spread, but if a high % of
the double bonds are hydrogenated, the texture of the margarine is a
bit like butter and the 'buttery effect' appeals to many consumers.
Instead of butter,
margarine and other partially hydrogenated vegetable oils are used
in processed foods because they are cheaper and gives food products
a longer shelf–life.
other 'spreadable' fats based on vegetable oils are quite a
mixture of molecules known as an
A typical mixture might be
fats (triglycerides with almost no double bonds in the hydrocarbon
monounsaturates in which there is about one double bond per
polyunsaturates which have more than one double bond per molecule.
In terms of
melting points, the order is saturates > monounsaturates >
and water ('salt' solution'), small amounts of protein and
carbohydrate and whey or buttermilk are added to the fat/oil mixture
together with an emulsifier.
To stop the salt
solution separating out from the 'oily' fats an
added, which keeps the aqueous salt solution dispersed in the
fats or they would separate into two layers and affect the look
Incidentally the emulsifiers may be mono– or di–glycerides of
fatty acids, that is molecules like the vegetable oils but only 1 or
2 fatty acids attached to the glycerol rather than 3, which leaves 2
or 1 –OH hydroxy groups on the glyceride molecule.
These emulsifying molecules have the
bifunctional structure (see diagrams D and E1 below) because through the action of intermolecular
forces they bind with both fats (via hydrocarbon chain,
'water hating' hydrophobic end of molecule) and bind with water
too (via hydroxy group OH, the 'water loving' hydrophilic
end of molecule). This double interaction with the oil/fat holds the emulsion or dispersion together and
stopping the formation of two layers (aqueous and oil/fat).
In margarine or
butter there will be far more of the oil/fat than water, but the
diagram is just meant to give an idea of how an emulsion is
stabilised. The diagram below is better representation of
margarine with its emulsifying agent which is often
monoglyceride or diglyceride esters of fatty acids. The hydrocarbon tails
sticking out from the minute water globules, make the water
compatible with the hydrogenated vegetable oils.
For a more general and wider description of emulsions
Aqueous solution chemistry
Examples of food labelling on
Spread 1 is made from vegetable fats and olive
oil. The oil/fat analysis shows it is a mixture of saturates,
monounsaturates and polyunsaturates. The total oil/fat is 59% by mass,
adding all the rest up means there is about 38% water in this oil in water
The labelling on this fat spread made from
vegetable oil is packed with nutritional information. Apart from the oil/fat
composition in spread 2 (assume similar in spread1) there added vitamins, salt, water, emulsifiers, flavourings etc.
etc. In spread 2 there is, by mass, 14% saturated fats, 15.9%
monounsaturated fats and 25.5% polyunsaturated fats.
Since fats and oils are important to our
diet, there is the ever present danger of over–consumption (speaking as
someone who loves chips and spicy crisps!).
So there are health and
social, as well as 'molecular' issues to address!
Vegetable oils are an important
source of energy and even vitamins like vitamin E in seed
Vegetable oils contain essential fatty acids which are bodies need for certain metabolic
So we need both oils and fats as sources of
important essential fatty acids and energy.
We need both saturated and unsaturated
fats or oils.
Animal fats tend to be
saturated molecules and vegetable oils tend to be unsaturated
The main sources of saturated fats
are from meat and dairy products e.g. 'dripping', butter, lard from
pork fat, blubber from whale fat, cod liver oil from fish, ghee
The main sources of unsaturated fats
are plant oils e.g. olive oil, walnut oil.
Animal fats are usually
solids at room temperature, though with low melting points, but
vegetable oils/fats tend to be liquids.
It is recommended that we do not
overdo the fat intake but we do need both saturated and unsaturated
Whatever fat or oil you use
in cooking – food preparation, you are significantly increasing your
calorie intake from these energy rich molecules and it doesn't matter
the oil/fat is polyunsaturated, partially hydrogenated or fully
In general unsaturated fats
are more healthy to consume than saturated fats and reduce the level of
cholesterol in your bloodstream.
However, too much saturated fat
raises cholesterol levels and is not too good for the heart –
increased blood pressure and poor blood circulation from blocked
arteries and heart disease can result from a diet high in saturated
animal fats – but you do need some and eating saturated fats in
moderation shouldn't be a problem.
Natural highly unsaturated
vegetable oils like walnut oil, olive oil, sunflower oil etc. do tend to
reduce cholesterol levels.
The consumption of trans
fats, and animal fats in general, increases the risk of coronary heart disease by raising levels
of LDL cholesterol and lowering levels of 'good' HDL cholesterol.
However even partially
hydrogenated vegetable oils contain 'trans–fats' which are not supposed to
be good for you, because they also tend to increase 'bad' cholesterol levels
and decrease 'good' cholesterol levels in your blood stream, and
therefore the risk of heart disease, so, eating lots of food containing
margarine etc. is not good for you!
of diet, food additives and cooking chemistry
what is it? How is it made? This is another use of
soap is a product of
the hydrolysis of fats
from animals and vegetable oils from plants
'Soapy' soaps (not modern detergents) are
the sodium salts of long chain fatty acids formed by heating fatty oils
with concentrated alkalis like sodium hydroxide or potassium hydroxide to hydrolyse them.
This is known as a saponification reaction and a typical equation is
above and the general word equation quoted below.
fat + sodium hydroxide ==> soap molecule + glycerol
This reaction breaks the fat molecule
down into one glycerol molecule (a triol alcohol) and three sodium salts of the long
chain carboxylic fatty acids that formed part of the original oil/fat ester.
- Examples of long chain 'carboxylic acids, known as 'fatty
acids', used to make soaps and detergents are shown
below ... where they typically have 16 to 20 carbon atoms in the chain
- ... with the 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.
- These salts are naturally formed on
hydrolysing the triglyceride triesters i.e. when the oil or fat is boiled
with sodium hydroxide solution (see equation above).
How do soaps and detergents work?
- The diagram above represents the
effect of mixing a soap/detergent with some clothes being washed.
- This diagram illustrates the mechanism
by which soaps wash oily/greasy clothes or surfaces.
- The 'neutral' end of the soap molecule
(hydrophobic, 'water hating') forms intermolecular bonds with the 'blob' of oil or grease, because they
are compatible at the molecular level.
- The other ionic negative end of the soap
molecule (hydrophilic, 'water liking') forms intermolecular bonds with water
(there would also be repulsion between the negative hydrophilic ends of
the soap molecule.
- The result is that the 'blob' of oil or grease
is surrounded by a coating of soap/detergent and is dislodged from the fabric surface and dispersed into the
washing water and hence can be washed away.
- This mechanism applies to washing greasy
dishes with 'washing-up-liquid' in the kitchen.
- The washing process is further described and
explained in more detail using the three
- Most traditional soaps are actually ionic
compounds which dissolve in water forming a long singly charged negative
ion (anion), which is balanced by a singly charged metal ion e.g. a
sodium ion, Na+.
- So soap molecules have a negative ionic hydrophilic 'head' ('water liking'/'oil
hating' end of molecule) and a
hydrophobic 'tail' ('water hating'/'oil liking' end of molecule').
- eg the stearate ion from the soap sodium
stearate shown above.
- When you shake soap with an oily/greasy
material (washing clothes or scrubbing a surface), the oil/grease breaks
up into tiny droplets or globules and removed from the surface to which
they were attached. Why? ...
- The hydrocarbon hydrophobic tail of the
soap dissolves in the oil or grease globule and the negative head is on
the surface of the globules/droplets but in contact with water.
- The long 'hydrocarbon' hydrophobic tail can only
interact at the molecular level with oil/grease ie is attracted to oil and grease
(its due to intermolecular forces, a bit like dissolving).
- The 'ionic' hydrophilic head can only
interact with water and forms weak bonds with water, just like when
ionic compounds readily dissolve in water.
- Two negative hydrophilic heads cannot interact
with each other and tend to repel each, but strongly interact with
- In effect, the soap anions allow
oil/grease and water to mix because the globules of oil/fat get a
surface coating of the soap and the negative end sticks out into the
water, and that end sort of dissolves in water.
- Therefore the oil/grease blobs
cannot remain attached to the fabric, or any other surface, and
become dispersed in the washing water, then washed away.
- This argument to any 'dirt' on any
surface that soap can interact with.
- A general name for these
molecules is surfactants and includes soaps, detergents and naturally
occurring non–ionic molecules like lecithin found in egg yolk.
- For more notes see
Emulsions, Paints and Pigments
Dry cleaning explained - no water involved!
- Dry cleaning is a washing process that
doesn't involve water, but uses other organic solvents.
- These organic solvents are better than
soaps/detergents in removing oil or grease stains from clothes or any
surface e.g. cleaning a metal surface before treating it in some way.
- These solvents will also remove stains that
will not dissolve in water.
- Unlike the complex action of soaps and
detergents in 'water washing', these solvents will completely dissolve the
oil, grease or stains.
- So, why is it that these solvents have
such useful and effective 'dissolving power'?
- When the organic solvent interacts with
oil/grease there are three lots intermolecular forces (weak intermolecular
bonds) operating, which are e.g. for oil ...
- solvent...solvent, solvent...oil
- and these three forces are all comparable in
- therefore, with an excess of solvent
molecules, the particles of the oil stain become surrounded by solvent
molecules and bond to them,
- so there is now a strong interaction between
the oil molecules and solvent molecules because of the intermolecular
- the solvated oil particles are now little
different that the solvent particles and are now very compatible with each
- AND this is the same as a dissolving process
and so all of the oil stain (and any other) is completely removed in a
Washing clothes at lower temperatures - biological detergents
- Biological washing powders or biological
detergents contain enzymes.
- Enzymes are biological catalysts which help
decompose, or break down, larger insoluble molecules (like food) into
smaller soluble molecules which can easily be removed in the washing
- Enzymes tend to work best at relatively low
temperatures (30oC to 40oC), so using biological
detergents to wash your clothes you can use a lower temperature for your
- Using a lower temperatures gives you several
advantages over using hotter water e.g.
- (i) you save on your energy (electricity)
- (ii) you can wash more 'delicate' items of
clothing and less chance of washing out fabric dyes.
- It should be noted if you wanted to do your
washing cycle at a higher temperature and still using biological detergents,
well, its NOT a good idea.
- These enzymes become denatured above 40oC
and wouldn't be very effective!
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
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