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Brown's Chemistry GCSE/IGCSE science-CHEMISTRY Revision
Oil, its many useful products, environmental problems and an introduction to
organic chemistry
14. 'Domestic' products - Oils, fats, margarine and soap organic molecules
Revise KS4 Science GCSE/IGCSE/O level
Chemistry Revision-Information Study Notes for revising for AQA GCSE Science, Edexcel
360Science/IGCSE Chemistry & OCR 21stC Science, OCR Gateway Science
(and courses equal to US grades 9-10)
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 and reactions :
10. Carboxylic acids and esters : 11. Addition
polymers and condensation polymers :
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 : 16. Ozone, CFC's and free
radicals : Extra notes, ideas and links on
Global Warming and Climate Change : Multiple Choice Quizzes: Oil Products (GCSE easier-foundation-level)
:
Oil Products (GCSE harder-higher-level) :
GCSE Aspects of Organic Chemistry
: and
3 Easy GCSE Oil Products word-fill worksheets
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Naturally Occurring Molecules from plants
and animals
14.
Fats, Oils and Margarine
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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.
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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).
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The carboxylic acids which
combine with the glycerol are described as 'long-chain fatty acids'.
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The resulting ester is called a
'triester' or 'triglyceride' and they are major components in animal
fat, vegetable oils, 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
acid).
-
Some sub-notes on Oil and Fat Structure:
(health
issues dealt with further down)
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They have the same linkages as Terylene but with different units.
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They are not as big as polymer molecules, but a lot bigger than a single
petrol or 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. The diagrams just assume three molecules of the same
'fatty' acid.
-
Monounsaturated fats have one C=C
double bond in them, polyunsaturated fats usually have at least
three 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
molecules.
-
However, this means these unsaturated
oils are not as conveniently 'spreadable' as 'butter'.
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To overcome
this problem, 'margarine'
was invented. The vegetable oils are reacted with hydrogen gas using
a nickel catalyst. Theses are called
hydrogenated fats
and have higher melting point so that they are a low melting
solid at room temperature rather than the sticky 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'.
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Saturated means
no double bond and unsaturated means double bond in this context.
-
The reaction for any double bond is: >CH=CH<
+ H2 ==> -CH2-CH2-, which is
converting an unsaturated part of the molecule to a saturated
structure.
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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!
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Margarine and
other 'spreadable' fats based on vegetable oils are quite a
mixture of molecules known as an
emulsion.
A typical mixture might be
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14-21% saturated
fats (triglycerides with almost no double bonds in the hydrocarbon
chains)
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15-30%
monounsaturates in which there is about one double bond per
molecule.
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14-22%
polyunsaturates which have more than one double bond per molecule.
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Sodium chloride
and water ('salt' solution'), small amounts of protein and
carbohydrate and whey or buttermilk are added to the fat/oil mixture.
-
To stop the salt
solution separating out from the 'oily' fats an
emulsifier is
added, which keeps the aqueous salt solution dispersed in the
fats or they would separate into two layers and affect the look
and
taste. 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 molecules have the
bifunctional structure 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) so
holding the emulsion or dispersion together.
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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!
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We need oils and fats as sources of
important essential fatty acids.
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We need both saturated and unsaturated
fats or oils.
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It is recommended that we do not
overdo the fat intake but we do need both saturated and unsaturated
fats.
SOAP

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