1. SIMPLE CHEMICAL REACTIONS
In This Section We Will Be Studying These Topics:
What is a chemical change and a physical change?
What are chemical reactions?
Acids with metals and non metals.
Testing for hydrogen gas.
How do acids react with carbonates?
Combustion and the products it makes.
Oxides of metals.
The special case of carbon dioxide.
Gases in the air. .

2. WHAT IS A CHEMICAL CHANGE?
All of the things around us can change. Wood and coal can burn and old bikes will rust in the rain. These changes are chemical changes.
We say that any new substances made are called PRODUCTS. These substances are made from chemicals combining together called REACTANTS.
This is a chemical change.
REACTANTS.
PRODUCTS.
Rust.

3. SOME CHANGES ARE NOT CHEMICAL
There are other changes around us that make substances change.
If there are no new products then these changes are called: PHYSICAL CHANGES
Melting is a PHYSICAL CHANGE. Water and ice are the same thing. There is no new PRODUCT made.
Chopping up wood is a PHYSICAL CHANGE. It is still wood but in smaller pieces.
Crushing rock or other substances is a PHYSICAL CHANGE. It is still the same but in smaller pieces or a powder.

4. WHAT ARE CHEMICAL REACTIONS?
When we cannot easily get the products back after a change then it is a sure sign that a chemical reaction has taken place.
The chemical reaction is what happens when a chemical change takes place and it usually takes in or gives out some energy.
We can look for signs of any changes.
There are 5 main signs we have to look for:
Colour.
Fizzing.
Smell.
It looks different.
It gets hot or cold.

5. PHYSICAL OR CHEMICAL CHANGE?
Look at the pictures and decide if they show a physical or a chemical change.
Chemical.
Lots of signs of a chemical change here.
Physical.
Melting.
Physical.
The wood does not change.
Physical.
If we evaporate the water it will leave the tea behind.

6. This gas floats away slowly and we do not see it.
ACIDS WITH METALS
In the unit about acids and alkalis you will have learned that acids can damage living tissue. This is a chemical reaction.
If we leave a metal out in the rain it will go rusty; the rain water contains carbonic acid and this, together with the air, reacts with the metal. Iron, air and rainwater produce rust
Acids also damage metals when they touch them; the acid and metal are changed and new products are made – a gas called hydrogen is produced.
This gas floats away slowly and we do not see it.
Being able to collect this gas would be a way of finding out if a reaction is taking place as some metals react very slowly with acid.

7. TESTING FOR HYDROGEN GAS
Hydrogen is a clear, colourless gas and it is lighter than air. It was once used to fill airships but it was so easy to set fire to that it was dangerous.
Find out what happened to an air ship called the Graff Zeppelin!
The hydrogen gas rises into the container.
If hydrogen gas is one of the products of a reaction between a metal and acid, then this can be collected by placing a container over the top of the apparatus.
To test for hydrogen gas you need to put a lighted splint under the gas.
If it ignites with a flash and a ‘squeaky pop’ then the gas is hydrogen.
The container is lifted and a splint is placed underneath.

8. WHAT HAPPENS WHEN AN ACID REACTS WITH A METAL?
Different metals react at different rates with the same acid.
The rate of the chemical reaction can be seen by the number of bubbles of hydrogen that are produced.
Here are some results from an investigation Masey and Mack did in class. They placed some metals in hydrochloric acid at room temperature.
Name of metal.
Number of bubbles of gas.
Most reactive to least?
Lead 6
Iron. 20
Silver.
none
Magnesium.
104
Zinc. 37
Fourth
Third
Least
Most
Can you work out the most reactive metal to the least reactive metal in the table?
Second

9. HOW DO ACIDS REACT WITH CARBONATES?
Acids are able to react with substances called carbonates. Carbonates are compounds of a metal with carbon and oxygen.
This gas can be collected.
When a carbonate reacts with an acid a chemical change occurs and a gas is given off from the reaction. The carbon and oxygen join together forming the gas carbon dioxide.
Hydrochloric acid + calcium carbonate Calcium chloride + carbon dioxide + water
Carbon dioxide can be detected using a liquid called limewater. It is water that has a substance called calcium hydroxide dissolved in it. When carbon dioxide is added to the limewater it changes the calcium hydroxide back into calcium carbonate and the clear limewater looks a cloudy white colour.
Limestone.
Chalk.
Calcium carbonate comes in lots of forms, here are three of them:
Marble.

10. TESTING FOR CARBON DIOXIDE
The bubbles pass along the delivery tube.
The bubbles of carbon dioxide turn the limewater cloudy.
The reaction between the acid and the piece of marble gives off bubbles of carbon dioxide.
Carbon dioxide gas is heavier than air and it sinks down. It is used to push air out of the way when we put a fire out with a fire extinguisher containing carbon dioxide.
Carbon dioxide can be used to put out electrical fires as it does not damage the equipment.

11. BURNING - IS IT A CHEMICAL REACTION?
Burning is a chemical reaction and the scientific term used for burning is ‘combustion’. There are signs we look for to see if a chemical reaction has taken place. They are:
It smells different and there was a smell as it was burning.
Burned paper turns to black.
Colour.
Smell.
Does it look different?
It has turned to ash and it is crumbly and flaky.
Temperature change?
The flames were very hot.
A new product has been made, it would not be possible to get the paper back.

12. THE PRODUCTS OF COMBUSTION
Fireworks burn and produce lots of heat as the reactants are so combustible that they are called explosives.
This chemical reaction is between the fuel in the fireworks and the air around them. It is the oxygen in the air that is reacting with reactants in the fireworks.
One chemical reaction that is taking place can be written like this:
Sulphur + oxygen sulphur dioxide
When the sulphur reacts with the oxygen it forms a new compound called sulphur dioxide.
Fuel
Heat
Oxygen
The sulphur and chemicals in the fireworks.
The gas in the air.
If the firework had burned in pure oxygen then the reaction would have been much more violent.
Setting the firework alight

13. What do you think the product from this reaction would be?
OXIDES AND METALS
From the fireworks we learned that sulphur and oxygen combine together to form a new product called sulphur dioxide.
When oxygen joins with a reactant to make a new product, it makes an Oxide.
Copper.
Copper is a metal that burns at a very high temperature.
What do you think the product from this reaction would be?
Copper oxide.
Name of the reactants
Name of the product
Zinc and oxygen.
Magnesium and oxygen.
Calcium and oxygen.
Iron and oxygen.
Zinc oxide.
In the table are some other metals. Can you work out the name of the product?
Magnesium oxide.
Calcium oxide.
Iron oxide.

14. THE SPECIAL CASE OF CARBON DIOXIDE
Non metals are also able to burn in oxygen and we started talking about combustion with sulphur.
Carbon dioxide is the gas we see in fizzy drinks.
There is another non metal called carbon. This is also able to react with oxygen. Sulphur formed a product called sulphur dioxide. What do you think the product of carbon and oxygen would be?
It can also be a liquid used in fire extinguishers.
Carbon dioxide.
It can be solid and is called dry ice. This is used for smoke machines in theatre productions.
All living things have carbon atoms in them. Non renewable fuels such as coal, oil and gas are made of carbon. When they burn they produce lots of carbon dioxide.
Non metals form oxides just like metals.

15. COOKING ON GAS + Fuel. Oxygen. Carbon dioxide. Water.
When we cook on gas we are using a fuel as a reactant. The fuel is made of hydrogen and carbon. This fuel comes to our homes in containers as a liquid or in pipes as a gas.
The fuel burns when we light it. We do not actually see a product. But that doesn’t mean they aren’t there!
The main products are:-
CARBON DIOXIDE (from the carbon part)
WATER (from the hydrogen part) – this evaporates and turns into steam.
There may be some other products from any impurities in the fuel.
Fuel.
Oxygen.
Carbon dioxide. +
Water.

16. OXYGEN IN THE AIR Size of jar (cm3) Amount the water went up by (cm3)
Not all of the air is oxygen. We know this because things burn more slowly in the air than in pure oxygen.
Mack and Masey have been waiting to see how long it takes for a candle to ‘go out’ inside different sized jars.
Each time they did this the water inside the jar went up. The bigger the jar was, the longer it took to go out.
Size of jar (cm3)
Amount the water went up by (cm3)
100 21
200 40
500
105
1000
220
Is there a relationship between the jar size and the amount the water rises up?
The rise is always about 20% of the size of the jar.

17. GASES IN THE AIR The air contains lots of gases.
The table shows us that oxygen is only about 1/5 or 21% of the air.
Name of gas
% in the air
Nitrogen 70
Oxygen 21
Carbon dioxide 4
Other gases 5

18. GASES IN THE AIR The air contains lots of gases.
In space there are no molecules of oxygen or other gases, so a fire cannot start. If we need to burn a fuel we have to take oxygen along to mix with the fuel so that it will react. The heat is used for movement in rockets.
Discussion.
Try to find out which gases the shuttles take with them to launch.
What do you think is in the three tanks?

19. WHAT HAVE WE LEARNED? That chemicals react with each other.
Chemical reactants react to make products.
There are five signs that a chemical reaction has occurred.
There are chemical and physical changes.
Acids react with metals and produce hydrogen gas. Some metals react faster than others.
Acids react with carbonates to produce the gas carbon dioxide. This gas turns lime water milky.
Metals burn to produce metal oxides.
Hydrocarbons burn to produce carbon dioxide and water.
Burning is a chemical reaction. For something to burn oxygen is needed.
Air is only about 20% oxygen.