KS3 Chemistry
9H Using Chemistry
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Contents
9H Using Chemistry
Chemical reactions
Burning fuels
New materials – everyday reactions
New materials – industrial processes
Summary activities
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Chemical reactions everywhere!
Chemical reactions take
place around you and
inside you all the time.
How many reactions
can you name?
Burning, rusting, cooking
and living all involve
reactions.
In a chemical reaction, reactants are changed into products
and new materials are formed.
Some chemical reactions are carried out to make new
materials and some reactions are used to release energy.
Are chemical reactions always useful?
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Useful chemical reactions
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Non-useful chemical reactions
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What’s that reaction?
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Contents
9H Using Chemistry
Chemical reactions
Burning fuels
New materials – everyday reactions
New materials – industrial processes
Summary activities
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Using combustion
Combustion is the chemical
reaction that takes place when
a substance burns.
The substance reacts with
oxygen and energy is released
as heat and light.
Combustion is an important
reaction as more than 90% of
the world’s energy comes from
burning fossil fuels like coal,
natural gas and petrol.
Where do fossil fuels come from
and what other fuels are there?
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Fire triangle
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Formation of fossil fuels – coal
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Formation of fossil fuels – oil and gas
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What’s the best fuel?
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Equations for combustion
Combustion, as the reaction of substance with oxygen, is also
called oxidation. The products of oxidation are oxides.
 Coal is mostly carbon. The product of burning coal is a gas
which turns limewater cloudy. What is the equation for
burning coal?
carbon
oxygen
carbon
dioxide
 Many fuels are hydrocarbons, which means they are made
up of carbon and hydrogen. When hydrocarbons burn
carbon dioxide and water (hydrogen oxide) are produced.
What is the equation for burning the hydrocarbon methane?
methane
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oxygen
carbon
dioxide
water
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Incomplete combustion
A good supply of oxygen is needed for a fuel to burn
completely and release as much energy as possible.
When carbon reacts completely with oxygen, it is all turned
into carbon dioxide. This is called complete combustion:
carbon
oxygen
carbon
dioxide
If there is not enough oxygen, a fuel cannot burn completely
and less energy is released. Some fuel is wasted.
When carbon does not react completely with oxygen, the
product is carbon monoxide, a colourless poisonous gas.
This is called incomplete combustion:
carbon
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oxygen
carbon
monoxide
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Contents
9H Using Chemistry
Chemical reactions
Burning fuels
New materials – everyday reactions
New materials – industrial processes
Summary activities
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Rusting reaction
Rusting is the reaction of iron with oxygen in the presence of
water. Salt helps to speed up the rate of this reaction.
Why does iron rust more quickly at the seaside?
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Preventing rusting
Rusting is the reaction of iron with oxygen in
the presence of water to form iron oxide (rust).
iron
+ oxygen  iron oxide
Rusting is an ‘unhelpful’ chemical reaction.
How do these measures help to prevent rusting?
 Iron that is exposed to the weather is usually coated with
a layer of paint.
The paint prevents oxygen and water getting to the iron.
 New products that contain iron are often boxed with a small
packet of drying agent.
The drying agent absorbs any water that may cause rusting.
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Making bread and alcohol
Yeast is a living organism which carries
out chemical reactions that are used for
making bread and alcohol.
 Yeast uses oxygen from the air for aerobic respiration:
glucose + oxygen  carbon + water (+ energy)
dioxide
The carbon dioxide gas produced in this reaction makes
bread rise by filling it with bubbles.
 Yeast can also carry out respiration without oxygen. This is
anaerobic respiration, which is also called fermentation:
glucose  carbon + ethanol (+ energy)
dioxide
Fermentation is used to produce alcohol in beer and wine.
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Ripening fruit
The ripening of fruit is a complex
collection of chemical reactions.
Take apples as an example:
 Starch is broken down into
sugars increasing sweetness.
 Acids are neutralized making
the apples less sour.
 Chlorophyll (green) changes to anthocyanin (red).
 Pectin, a chemical which makes apples hard, is broken
down and so makes the apples softer.
Why do food producers and supermarkets need to know
about the conditions and reactions involved in ripening fruit?
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Ripening fruit
The ripening of all fruit and vegetables involves similar
chemical reactions.
The speed of ripening is affected by the temperature and by
the presence of a chemical called ethene.
Food producers and supermarkets know the best conditions
for slowing down or speeding up the ripening process so that
fruit and vegetables do not go off too soon.
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Cooking eggs
Cooking involves chemical reactions – changes colour, taste
and texture due to atoms in food joining together in new ways.
Cooking an egg changes it texture from runny to firm:
Eggs contain a protein called albumen. The protein molecules
are long chains of amino acids folded into a ball shape.
When eggs are heated, some of the protein atoms break apart
and the molecules unfold. These molecules then join to other
nearby protein molecules until they are all linked in a network.
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Food spoilage
Chemical reactions are not always useful. The changes that
take place as food “spoils” are caused by chemical reactions.
Apples turn brown when exposed to the air because they
react with oxygen in the air.
Knowing what causes this reaction can help to slow it down:
 Placing sliced apples in water prevents browning
because the apples are no longer exposed to air.
 The chemical ascorbic acid (vitamin C), found in lemon
juice, is also known to prevent the browning reaction.
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Contents
9H Using Chemistry
Chemical reactions
Burning fuels
New materials – everyday reactions
New materials – industrial processes
Summary activities
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Making plastics from oil
Plastics are very useful materials
that are made by chemical reactions
in factories.
The starting materials for making
plastics come from crude oil, which
is found in the Earth’s crust.
When crude oil is pumped out of the
ground (or sea bed) it is a mixture of
chemicals called hydrocarbons.
Crude oil is separated into different
hydrocarbons at an oil refinery using
a process called fractional
distillation.
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Crude oil and fractional distillation
Fractional distillation separates crude oil based on the different
boiling points of the hydrocarbon molecules.
Small molecules boil at lower temperatures than bigger ones.
boils at a
boils at a
lower
higher
temperature
temperature
The crude oil is heated and molecules of different sizes boil at
different temperatures. These gases are collected separately
and cooled, condensing to form different fractions.
Some of the fractions obtained from crude oil, listed in order
of increasing boiling point, are:
fuel gas, petrol, naphtha, kerosine, diesel and bitumen.
Which of these fractions has the biggest molecules?
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Fractional distillation animation
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Fractional distillation activity
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Making plastics by polymerization
The separated hydrocarbons obtained
from the fractional distillation of crude
oil have many uses.
One of the main uses of the smaller
hydrocarbon molecules obtained is
to make plastics.
Plastics consist of very long chains
called polymers.
The chemical reaction in which small
molecules join together to make these
very long polymer molecules is called
polymerization.
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Making plastics
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Making metals by smelting
Metals are very useful materials
but many metals are found in
rocks as compounds called ores.
Iron, which is used to make steel,
is found in the earth as iron ore.
By heating the iron ore (mainly iron oxide) with carbon, the
iron can be extracted.
iron
oxide
+ carbon 
iron
+ carbon
dioxide
The carbon displaces the metal in a process called smelting.
This process is the reverse of oxidation as the oxygen is
taken away from the metal. It is called a reduction.
In the reaction above, the iron oxide is reduced to iron.
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Blast furnace animation
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Electrolysis
Electrolysis is a chemical reaction that uses
electricity to break up a compound and is
another method for extracting a metal from
its ore.
For example, aluminium cannot be extracted
by smelting and so electrolysis is used to
aluminium metal from aluminium oxide.
aluminium oxide
 aluminium + oxygen
During electrolysis, the metal is always formed as a coating
on the electrode that is connected to the negative electrode
(the cathode.)
This is why electrolysis is also used for the purification of
copper and for electroplating other metals.
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Electrolysis animation
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Contents
9H Using Chemistry
Chemical reactions
Burning fuels
New materials – everyday reactions
New materials – industrial processes
Summary activities
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Glossary
 combustion – The reaction of a substance with oxygen
which releases heat and light energy.
 electrolysis – A reaction that uses electricity to break up
a compound and can be used for extracting metal.
 fuel – A substance that is burnt to provide energy.
 fractional distillation – The process used to separate
a mixture, such as crude oil, into its components which have
different boiling points.
 hydrocarbons – Compounds that are made up of the
elements carbon and hydrogen only.
 polymers – Materials, such as plastics, that are made up
of very long molecules.
 smelting – Heating a metal ore with carbon to extract the
pure metal.
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Anagrams
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Multiple-choice quiz
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