carbon dioxide +
ethanol.gcsescience.com 17 gcsescience.com
Catalysts - Enzymes.
Fermentation.
Yeast
is a microorganism containing an
enzyme which will convert
a sugar
(glucose) solution
into carbon dioxide and alcohol (ethanol).
The word equation for fermentation is
glucose + yeast
carbon dioxide +
ethanol.
Carbon dioxide
gas bubbles out
of the solution into the air
leaving a mixture of ethanol and water.
Ethanol can be separated from the mixture by fractional distillation.
Fermentation must be carried out in
the absence of air to make
alcohol.
If air is present, ethanoic acid is made instead of alcohol.
Yeast
is used in a batch process to make alcohol in beer and
wine.
An enzyme in yeast acts
on the natural sugar
in
malt (to make beer) and grapes (to
make wine).
When the alcohol concentration reaches about 10%,
the alcohol damages the yeast and
fermentation stops.
In a batch process the reaction
vessel must be emptied and
cleaned
and then refilled with the
new starting materials. A batch process
takes more time and is
more expensive than a continuous
process.
Different alcoholic
drinks contain different
amounts of alcohol.
Some people drink alcohol for
enjoyment, some drink to excess
and some people become addicted to
alcohol.
The harmful effects (physical and social)
of drinking excess alcohol
are widespread and reach all parts of
society.
Ethanol can be made on a large scale for use
as a fuel or
solvent
by the hydration of
ethene or the fermentation of sugar
cane.
Sugar cane is a renewable resource.
Renewable means that the resource can be replaced.
For example more sugar cane can be grown.
Compare this with the use of fossil fuels (the source of ethene)
which are a non-renewable resource.
Yeast
is used in the baking of bread.
The carbon dioxide produced causes the
bread to rise
and fills the bread full of bubbles.
The alcohol evaporates during the baking
process.
Yoghurt and Cheese.
Bacteria can be added
to milk to make yoghurt.
An enzyme in the bacteria reacts with
sugar in the milk (called lactose)
and converts it into lactic acid.
Lactic acid changes milk proteins and forms the thicker yoghurt.
Cheese is made by adding an enzyme called rennet
after bacteria have produced
lactic acid in milk.
Rennet makes milk proteins turn solid and this is the basis for cheese.
Rates of
Reaction Enzymes Search Questions 
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