West Lothian Council
Lorna C. Webster
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Corrosion of metals
What is corrosion?
Read
You have already learned about some chemical reactions
 burning is a reaction that makes heat. The
scientific word for burning is combustion.
 neutralisation is the reaction of an acid to make water.
Corrosion is a chemical reaction that involves metals. When a
metal corrodes it is eaten away chemically and the surface of
the metal changes from an element into a compound.
Rusting is a special type of corrosion. Rusting is the name we
use for when iron rusts. The word rusting can be used for steel
because steel is an alloy made from iron and carbon but the
word rusting should not be used for any other metal.
Your teacher may show you a video about rusting (SS18).
Write a heading and try the work below.
1. What is the name of the reaction that produces heat?
2. What is the name of the reaction where and acid reacts to
make water?
3. What happens to metals in the reaction that is called
corrosion?
4. Why is rusting a special type of corrosion?
5. Why can we use the word rusting for steel but not for any
other metals?
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What causes rust?
Read
Most people think water causes rusting. Experiments can be
set up to test this. Look at the display (2.14) called "what
causes rust".
oil
A
boiled water
water
drying
chemical
B
C
NOTE:
 Tube A: contains a special chemical that absorbs water to
make sure that the oxygen in the tube is dry.
 Tube C: Gases like oxygen dissolve slightly in water. This
dissolved oxygen can be removed by boiling the water. Oil is
put on the surface to stop oxygen dissolving again.
Write a heading and try the work below.
1. Draw a diagram of the experiment.
2. Why has the water in tube C been boiled?
3. Why is there a layer of oil on the surface of the boiled water
in tube C?
4. Copy and complete the table below.
test tube
water
present?
oxygen
present?
A
B
C
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rust?
5.Copy and complete the sentence below.
This experiment shows that for iron to rust both
_________ and _________ must be present.
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looking for rust
Read
To see whether a piece of iron has rusted is
easy. All we need to do is to look for a brown
substance forming on the iron but this can take
a long time. Scientists need quicker ways to
find out whether a piece of iron is beginning to
rust. To do this they use an indicator.
Indicators
You have already found out about pH indicator in chemistry. pH
indicator changes colour depending on whether a substance is
acid, alkali or neutral. The following experiment is to find out
the name of an indicator that will change colour depending on
whether there is rust or not.
Collect:
a test tube rack
4 test tubes
1 glass rod
1 bottle of rust solution
1 bottle of each indicator (labelled A, B, C, D)
4 droppers (one for each indicator)
Set up the experiment as shown in the diagram below:
rust solution
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Now add 20 drops of
indicator A to the first tube,
B to the second tube,
C to the third tube,
D to the fourth tube
Use a fresh
dropper each
time!
Mix each tube with a clean glass rod each time and watch to see
what happens.
Write a heading and try the work below in your jotter.
1. Why do scientists need an indicator to show them if iron is
rusting?
2. From your experiment which indicator (A,B,C or D) changed
colour when it was put into rust?
3. What colour was this indicator before you put it into the
rust?
4. What colour did it change to when it touched the rust?
5. Ask your teacher to tell you the names of the chemicals that
were in the indicator bottles and copy and complete the
sentences below.
The name of the indicator that can be used to find rust is
called ________ indicator. Rust indicator changes from
____________ to __________ if rust is present.
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Changing the speed that iron rusts
Read
If you've ever been to Florida or Arizona you may have noticed
that there are many very old cars that are still in excellent
condition. This is something that is rare in Britain. Most old
cars have rusted and have been sent to the scrapyard.
Iron rusts at different speeds depending on the conditions
that it is in.
The aim of the following experiment is to find out if iron
rusts faster than normal when it is acid and when it is in
salt.
Write a heading then do the following experiment.
Collect 4 test tubes
a test tube rack
4 clean iron nails
1 bottle of salty water
1 bottle of acid rain (1mol/l hydrochloric acid)
1 bottle of rust indicator
1. Set up the test tubes in a rack.
2. Half fill each test tube with the solutions as shown in the
following diagram.
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tap
water
acid
rain
The test tube in the
experiment that contains
tap water is needed to see
how fast the iron rusts
when it is not in acid or
salt.
salty
water
3. Add enough rust indicator to each tube and mix each tube
with a clean glass rod each time to give a yellow colour.
4. Put a nail into each tube and watch what happens.
Now try the work below in your jotter.
1. What was the aim of the experiment?
2. Why was the tap water test tube included in the experiment?
3. How could you tell if the iron had rusted or not?
4. Draw a diagram of the test tube rack to show the nails and
colour the tubes in blue to show how much the rust indicator
changed colour.
5. Copy the following sentences and circle the correct words.
Acid rain speeds up/slows down rusting.
Salt water speeds up/slows down rusting.
6. In the winter salt is spread on the roads
to help stop them being icy. What will
this do to the speed that the car will
rust?
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7. John lives near the beach at St Andrews. His brother lives in
Armadale. Even though both brothers bought their new cars
on the same day John
noticed that his was rusting
faster than his brother's.
Can you explain this?
8. You should already remember that acid rain is
caused by nitrogen dioxide gas from car
exhausts dissolving in cloud water. Explain
why cars that are in cities rust faster than
cars that are in country areas.
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Stopping rust
Read
When a metal corrodes it becomes weakened. This can cost a
lots of money because the weakened parts need to be replaced
so it important to try to find
ways to stop corrosion.
You should already know that for
iron to rust it has to be in contact
water
with oxygen and water. This
oxygen
means that one way to protect
iron from rusting is to put a
barrier between the iron and the
oxygen and water. There are
many types of coatings that we
can use to cover the iron. To find
coating/barrier
out if they work try the
experiment below.
Iron
Collect:
a test tube rack
5 test tubes
1 glass rod
1 bottle of rust indicator
1 bottle of salty water
1 ordinary nail
1 plastic coated nail
1 galvanised nail
1 greased nail
1 painted nail
1. Set up 5 test tubes in the rack and half fill them with salt
water.
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2. Add enough rust indicator and mix it into the salty water
with a glass rod to give a yellow colour in each tube.
3. Put the different nails into each tube as shown in the
diagram below and observe what happens.
ordinary
nail
plastic
coated
nail
grease
coated
nail
paint
coated
nail
galvanised
nail
An ordinary nail is needed in this experiment to allow you to see
how much rusting happens without any coating.
Write a heading and try the work below.
1. Copy the diagram of the experiment into your jotter and add
blue colour to show how much rusting has happened.
2. Why was an ordinary nail needed in the experiment?
3. Copy and complete the notes below
Coating iron with a substance stops iron from rusting
because the coat stops the ____________ and
____________ in the air touching the iron.
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Galvanising
Read
Galvanised iron is iron that has been coated with a metal called
zinc. To do this the zinc is heated up until it
Zinc
melts and then the iron is dipped into it. The
iron is then lifted out and when the melted
zinc cools, it turns into a solid coating.
Galvanising is used to coat iron nails, chisels
and motorway crash barriers. This is useful
because if the zinc is scratched, the iron will
still not rust. Paint would be no use for a
crash barrier because if the paint is scratched the iron would
start to rust.
Iron
Write a heading and try the work below.
1. When iron is galvanised, what is the name of the metal that it
is coated with?
2. If you had an iron nail, a lump of solid zinc and the normal
apparatus that is in the lab how you would galvanise the nail?
3. Give two uses of galvanised iron.
4. Why is galvanised iron better for crash barriers than painted
iron?
5. Copy the following table and complete it by looking at the
"coatings in use" poster.
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coating
tin-plate
uses
crash barriers, chisels
and dustbins
greasing
electrical wiring
washing-up racks
clothes hangers
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Electroplating one metal with another
Read
You should already know that iron is coated with zinc when it is
called galvanising but to stop iron rusting, it can also be coated
with other of metals.
You have probably heard of silver-plated
jewellery and gold-plated jewellery. This is a
cheaper way to make jewellery than using solid
silver or gold.
The shiny bumpers on cars or bathroom taps are often coated
with a metal called chromium.
This helps stop rusting and also
makes the bumpers and taps look
good.
To plate silver, gold or chromium onto other metals we use
electricity. This process is called electroplating.
Write a heading and do the work below.
1. List some everyday examples of coating one metal with
another metal.
2. Why do some shops sell silver-plated and gold-plated
jewellery instead of solid silver or gold?
3. What is the process called that uses electricity to coat one
metal with another?
In the next experiment you are going to try to coat a 10p piece
with another metal.
Collect:
a power pack and plug
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2 wires
2 crocodile clips
a copper strip
a 10p piece
a petri dish
a bottle of copper chloride solution
Set up the experiment as shown in the diagram below but do
not switch the power on until you read the next instruction.
power pack
+ 4V DC
-
_-
10p
copper strip
You need to
connect the leads
to the red and
black connections.
Red = +
Black = -
petri dish
copper chloride
solution
Place the 10p piece into the copper chloride solution and hold
the plastic part of the wire. DO NOT put the crocodile clips
into the solution and DO NOT touch the 10p and the copper
strip together.
power pack
+ 4V DC
-
_-
copper strip
10p
petri dish
copper chloride
solution
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Switch the power on and observe what happens to the 10p
piece.
4. Draw a diagram of the experiment (copy the second diagram
on page 4).
5. What did you see happen to the 10p piece?
6. Why do you think this happened?
7. A pupil wanted to set up an electroplating experiment to coat
a 10p piece with tin. Copy and complete the labels in the
diagram below to show how he would do this.
power pack
+ 4V DC
-
_-
______ strip
_____
______chloride
solution
petri dish
Protecting aluminium from corrosion
Read
Aluminium is a metal that has a great many uses. It is light so it
is used to build aeroplanes. It is very important that the
aluminium does not corrode quickly
or the aircraft would soon become
unsafe and this would be a danger
to the crew and passengers.
Scientists have found that if they leave a piece of aluminium
outside, the surface of the aluminium reacts slowly with the
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oxygen of the air. This turns the surface of the aluminium into
a compound called aluminium oxide.
aluminium
thin aluminium oxide layer
after several days
aluminium before it is
put outside
Scientists discovered that the aluminium oxide layer protected
the aluminium underneath from corrosion. They worked out a
way to make this aluminium oxide layer thicker. This process is
called anodising.
The main point of anodising is that it protects the aluminium
from corroding but another advantage is that the layer can be
painted to make the aluminium look more attractive.
Write a heading and try the work below.
1. Collect a data book and look up the data book contents page.
What page would you look at to find out about the uses of
metals?
2. Use the data book to make a list of the uses of aluminium.
3. Why is it important that aluminium does not corrode in
aeroplanes?
4. What did scientists discover happened to aluminium if it is
left outside?
5. Copy the diagram to show what happens to a piece of
aluminium if it is left outside.
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6. Copy and complete the sentences below into your jotter.
To stop aluminium corroding the thin alumimium oxide layer
on the outside is made t__________. This process is
called a______________.
7. Apart from stopping the corrosion of aluminium, what other
advantage is there to anodising?
Attaching other metals to stop rusting
Read
Up to this point you have learned that we can stop corrosion by
completely covering one metal with another to act as a barrier
to the oxygen and water in the air. This is not the only way to
stop rusting. We can change the speed of rusting by attaching
iron to other metals. With some metals we can stop the
rusting even if most of the iron is still touching water and
oxygen.
Write a heading and look at display 2.21.
1. Copy and complete the table on the next page to show what
you saw in the display and colour in each diagram in the table
to show how much blue colour there is.
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diagram of the
experiment
metal attached to
the iron
rust (yes or no)
No metal attached
magnesium
zinc
tin
copper
2. Why do you think a nail on its own was used in this
experiment?
3. Which metals speeded up the rusting of iron?
4. Which metals stopped the iron from rusting?
5. Copy and complete the sentence below by choosing the
correct answer. (you should use the data book page 6 to help
you if necessary).
Iron does not rust if it is attached to a metal that is more/less
reactive. This works even if the iron is not completely covered.
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6. Collect and read the information sheet called "Stopping
corrosion - everyday examples" and try to answer the following
questions.
a) What is the main problem with using metals?
b) Explain how barrier protection works.
c) List some examples of where painting is used to stop
corrosion.
d) What type of coating is used to stop bicycle chains
rusting?
e) Why is paint not good for using on car engines?
f) What are the names of the two scientific ways to coat
one metal with another?
g) List some examples where plastic coating is used to stop
rusting.
h) Ships are often painted to help stop corrosion but why
do they rust very quickly if the paint is scratched?
i) What is done to help stop ships rusting even if the paint
is scratched?
j) Why is paint no good for protecting underground
pipelines?
k) What is done to stop the pipelines rusting?
l) What is the process called that is used to stop
aluminium corroding?
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