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Macromolecules
(polymers)
Francine
Taylor-Campbell, Contributor
IMPORTANT
POINTS
- Polymerisation
is the formation of a large molecule
from smaller units called monomers.
- Monomers
containing the C=C can add together
to form polymers (addition) or two
units can react together to eliminate
a small molecule such as water (condensation).
- Polysaccharides
such as starch can be broken down
to simple sugars (monosaccharides)
by enzymes (such as amylase) or
during acid hydrolysis
- Proteins,
polyesters and polyamides are all
formed from condensation polymerisation.
- Hydrolysis
is the breakdown of large molecules
to small ones by reaction with water.
This can be done in the presence
of an acid.
- When
sugars are fermented in the absence
of oxygen, ethanol is produced.
- Fractional
distillation can be used to produce
pure ethanol from the products of
fermentation.
Let
us now revise the important aspects
of organic chemistry by attempting
some questions!
Question
1
1.
Ethanol is widely used in industry
as a solvent, a fuel and in alcoholic
beverages.
(i)
Suggest two reasons why ethanol may
be considered a better fuel than gasolene
and one reason why it is not widely
used.
(ii)
Suggest one reason for ethanol being
completely soluble in water.
(iii)
How would you obtain a purer sample
of ethanol from a mixture of ethanol
and water?
(iv)
Outline the chemical principles involved
in the breathalyser test for the determination
of alcohol (ethanol) blood levels
in automobile drivers.
ANSWERS
1.
(i) Ethanol and gasolene burn in air
to produce carbon dioxide and water.
Gasolene contains other substances
such as sulphur compounds and so on;
combustion can produce the oxides
of sulphur as well as other products
that can increase air pollution. Ethanol
is a cheaper and cleaner fuel than
gasolene and is produced from sugar
cane and beet, which are renewable
resources. Ethanol may not be widely
used as it may burn faster than gasolene
and release less energy.
Comment:
Mixing ethanol and gasolene may help
it to release more energy while reducing
harmful products from entering the
atmosphere.
(ii)
Ethanol and water have similar structures,
that is, the presence of the OH group.
C2H5-OH (ethanol)
and H-OH (water).
This
means that water can form hydrogen
bonds with itself and with ethanol,
which causes the ethanol to dissolve
in the water.
(iii)
A mixture of ethanol and water is
described as a mixture of miscible
substances which can only be separated
by fractional distillation.
(iv)
In the breathalyser test, alcohol
from a person's breath reacts with
a chemical substance called potassium
dichromate which has been acidified.
The alcohol is oxidised by the dichromate
crystals which change from an orange
colour to green. The concentration
of alcohol is determined by the length
of the green colour in the tube containing
the dichromate crystals. In the reaction,
ethanol is converted to ethanoic acid
and the dichromate ions are reduced
to chromium (Cr3+) ions.
Continue
to revise and we will attempt some
more questions in the next lesson.
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DRUMMING
UP A STORM: Ascot High School
drummers in action during the
Portmore Healthcare/Black History
Month Concert at the Portmore
HEART Academy in Portsmouth
recently.
- Anthony Minott/Freelance Photographer
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Francine
Taylor-Campbell is an independent
contributor.
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