© Boardworks Ltd 2004 1 of 20 © Boardworks Ltd 2005 1 of 37 KS3 Chemistry 9H Using Chemistry

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KS3 Chemistry

9H Using Chemistry


Contents

9H Using Chemistry

New materials – everyday reactions

Summary activities

New materials – industrial processes

Chemical reactions

Burning fuels


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?


Useful chemical reactions


Non-useful chemical reactions


What’s that reaction?


Contents

9H Using Chemistry


Summary activities


Chemical reactions

Burning fuels


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?

Using combustion


Fire triangle


Formation of fossil fuels – coal


Formation of fossil fuels – oil and gas


What’s the best fuel?


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 dioxideoxygencarbon

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?carbon dioxideoxygenmethane water


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 dioxideoxygencarbon

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 monoxideoxygencarbon


Contents

9H Using Chemistry


Summary activities


Chemical reactions

Burning fuels


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?


Iron that is exposed to the weather is usually coated with a layer of paint.

New products that contain iron are often boxed with a small packet of drying agent.

iron oxideoxygen+iron

Preventing rusting

Rusting is the reaction of iron with oxygen in the presence of water to form iron oxide (rust).

Rusting is an ‘unhelpful’ chemical reaction.How do these measures help to prevent rusting?

The paint prevents oxygen and water getting to the iron.

The drying agent absorbs any water that may cause rusting.


Yeast uses oxygen from the air for aerobic respiration:

The carbon dioxide gas produced in this reaction makes bread rise by filling it with bubbles.

Making bread and alcohol

Yeast is a living organism which carries out chemical reactions that are used for making bread and alcohol.

Yeast can also carry out respiration without oxygen. This is anaerobic respiration, which is also called fermentation:

Fermentation is used to produce alcohol in beer and wine.

energy)water+carbon dioxide

oxygen+glucose (+

energy)ethanol+carbon dioxide

glucose (+


Ripening fruit

Starch is broken down into sugars increasing sweetness.

Acids are neutralized making the apples less sour.

The ripening of fruit is a complex collection of chemical reactions. Take apples as an example:

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?


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 thatfruit and vegetables do not go off too soon.


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.


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.

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.


Contents

9H Using Chemistry


Summary activities


Chemical reactions

Burning fuels


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.


Fractional distillation separates crude oil based on the different boiling points of the hydrocarbon molecules.

Small molecules boil at lower temperatures than bigger ones.

Crude oil and fractional distillation

boils at a higher temperature

boils at a lower 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?


Fractional distillation animation


Fractional distillation activity


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.


Making plastics


iron oxide

+ carbon iron + carbon dioxide

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.

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.

The carbon displaces the metal in a process called smelting.


Blast furnace animation


oxygen+aluminiumaluminium oxide

During electrolysis, the metal is always formed as a coating on the electrode that is connected to the negative electrode (the cathode.)

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.

This is why electrolysis is also used for the purification of copper and for electroplating other metals.


Electrolysis animation


Contents

9H Using Chemistry


Summary activities


Chemical reactions

Burning fuels


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 thepure metal.


Anagrams


Multiple-choice quiz

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© Boardworks Ltd 2004 1 of 20 © Boardworks Ltd 2005 1 of 37 KS3 Chemistry 9H Using Chemistry