Notes

1. MUST KNOW THESE TOPICS FOR THE CXC EXAMS
Rusting
 Rusting is the oxidation of iron to form hydrated iron (III) oxide.
Note:
-The corrosion of iron is called rusting AND it is an oxidation reaction.
-Only iron(and alloys containing iron) will rust. Other metals(eg. Mg etc) corrodes.
 When an object made of iron (eg. iron, mild steel) is exposed to moist air for some time,
a reddish-brown substance (rust) slowly forms on the surface, through rusting-corrosion
of iron.
 Rusting occurs only in the presence of both oxygen and water. Rusting can be
speeded up by the presence of sodium chloride and acidic substances [eg. acidic
oxides(SO2, SO3, CO2)that will form acid solutions] .
 A simplified equation for the formation of rust is:
4Fe + 3O2(g) + 2H2O → 2Fe2O3.xH2O(s)
(rust)/orange-brown colour
(1) Put an iron nail in pure water, but exposed to air. Lots of rust after a few days. The
nail is well exposed to water and the oxygen in air.
(2) Put an iron nail into boiled water in a sealed tube, and a layer of oil too. The boiling
drives off dissolved air and the oil provides an extra barrier. Very little rusting after a few
days. If you do it very carefully, it can be quite some time for any rusting to show up.
This shows with the oxygen from air, rusting will not happen.
(3) Put an iron nail in a sealedtest tube of air and a drying agent (e.g. anhydrous
calcium chloride, absorbs any moisture), very little, if any rusting even after quite a few
days. The absence of water prevents rusting taking place.
(4) Put a nail in a test tube, but just exposedto air. Very little, if any, rusting observed.
BUT it will eventually rust because there is water vapour in the air

2. Rust Prevention
Method Description
Using a protective layer - The metal is coated with a layer of substance that stops water
and air from reaching the metal.
- This is done by painting, greasing, and coating with another
metal.
- For example, in galvanizing (or zinc plating), a thin film of
zinc is used to cover the iron. Note: even if the zinc layer is
damaged/scratched, the iron will not rust because zinc is more
reactive than iron and it will corrode in place of iron (the more
reactive metal corrodes preferentially).
Using a sacrificial metal
(sacrificial protection)
IMPORTANT: KNOW
FOR CXC EXAMS
- Involves attaching a more reactive metal (eg. magnesium, zinc
etc) to iron. Since Mg or Zn is more reactive than iron they both
will preferentially corrode in place of the iron because Mg and
Zn lose their valence electrons more readily than iron. As long
as a more reactive metal is present the iron will not corrode
(rust).
Applications: Bars of zinc are attached to a ship’s hull to
prevent the ship’s steel body from rusting, attaching magnesium
blocks to underground pipes.
Using alloys - Stainless steel which is a rust resistant alloy, can be used. On
exposure to air and moisture, the chromium metal in the alloy
will form a very hard coating of chromium(III) oxide on the
surface of the stainless steel, preventing it from further
corrosion.
Recycling of Metals
Note: This is important for Green Chemistry as well.
 Metals are finite resources and need to be conserved.
 The amount of metal ores in the Earth’s crust is limited. If metal extraction continues at
present rates, the supplies of many metals will run out. Hence, there is a need to recycle
metals.

3. The Economic, Social and Environmental Advantages/Disadvantages of Recycling Metals
Advantages Disadvantages
Economic - It saves the cost of
extracting new metals from
their ores.
- Fewer landfills to dispose
used metal objects will need
to be built. This saves the cost
of building landfill sites.
- It is very expensive,
considering other processing
costs like collecting,
transporting and separating
the scrap metals.
Social - It helps to conserve the
limited amount of metals in
Earth.
- With the increasing world
population, more land will be
available if ore mining is
reduced.
- It takes time and effort for
the world to practice
recycling as a way of life.
Environmental - Reduces the environmental
problems related to extracting
metals from ores (eg. waste
gases including carbon
monoxide which are formed
in the blast furnace through
iron extraction will be
reduced).
- The recycling process may
cause pollution if not done
properly (eg. metal fumes
from the recycling process).
Question 1 Fill in the blanks is EACH sentence by using the CORRECT words given below.
alloy chromium faster first flake less oil oxidation oxide oxygen
paint reactive rusting sacrificial stainless water zinc
1. Iron (or steel) unfortunately corrodes than most other transition metals and readily
does so in the presence of both (in air) and to form an iron
.. Iron corrosion is called and the chemical change with oxygen is called an
reaction.
2. Iron and steel (an of iron) are most easily protected by which provides a
barrier between the metal and air/water. Moving parts on machines can be protected by a water
repellent or grease layer.
3. This corrosion can be prevented by connecting iron to a more metal (e.g. zinc
or magnesium). This is called protection. By mixing iron with other metals such
as you can make a non-rusting alloy called steel. Coating iron
or steel with a layer is called 'galvanising'. The zinc preferentially corrodes

4. first to form a zinc oxide layer that doesn't off. However if a reactive
metal is attached, the iron then rusts as it becomes the more metal!
2.
Figure 2 shows four test tubes a student set up to investigate the rusting of iron.
This is the method used for each test tube.
Measure the mass of the nail using a balance.
Leave the nail in the test tube for 6 days.
Measure the mass of the nail after 6 days.
Table 2 shows the student’s measurements.

5. 2.1) What is the resolution of the balance the student used? [1 mark]
Tick one box.

6. 2.2) Calculate the difference in percentage increase in mass after 6 days of the nail in test tube 1
and the nail in test tube 5.
Give your answer to three significant figures. [4 marks]
Difference in percentage increase in mass = _______________________ %
2.3) Use the results of the student’s investigations to draw conclusions about the factors affecting
the rusting of iron. Include an evaluation of the effectiveness of different coatings at preventing
the rusting of iron. [6 marks]
Simple Statements(Hint: Make reference to which test tube rusting occurred or did NOT
occur, what conditions prevented or cause rusting to occur(which test tubes had air/oxygen
and water)
a. ___________________________________________________________________________
b. ___________________________________________________________________________
c. ___________________________________________________________________________
d. ___________________________________________________________________________
e. ___________________________________________________________________________
f. ___________________________________________________________________________
g. ___________________________________________________________________________
Conclusions: (Hint: What factors are required for rusting to occur, how does oil, paint and
galvanizing the iron nail prevents the iron nail from rusting, why the nail will NOT rust when the
galvanized nail is scratched, does painting offer better protection for the iron nail than
galvanizing.)
a. ____________________________________________________________________________
b. ____________________________________________________________________________
c. ____________________________________________________________________________
d. ____________________________________________________________________________
e. ____________________________________________________________________________
f. ____________________________________________________________________________
g. ____________________________________________________________________________
h. ____________________________________________________________________________

7. i. ____________________________________________________________________________
j. ____________________________________________________________________________
Evaluation: (Hint: How effective are oil and painting in preventing rusting? Is galvanizing
more effective than oil and painting in preventing rusting.)
_________________________________________________________________________
_________________________________________________________________________
_________________________________________________________________________
_________________________________________________________________________
_________________________________________________________________________
_________________________________________________________________________
2.4) Rust is hydrated iron(III) oxide.
Complete the word equation for the reaction. [2 marks]
________________ + ________________ + ______________ → hydrated iron (III) oxide
WORK SMART (BE PRODUCTIVE) TO ACHIEVE MORE !