IGCSE, air and water, chemistry

1. Air and Water
Grade 10 IGCSE Chemistry

2. What you need to be able to do and
understand:
Describe a chemical test for water.
Describe and explain, in outline, the
purification of the water supply by
filtration and chlorination.
State some of the uses of water in
industry and in the home.
Describe the separation of oxygen
and nitrogen from liquid air by
fractional distillation.
Describe the composition of clean air
as being a mixture of 78% nitrogen, 21%
oxygen and small quantities of noble
gases, water vapour and carbon
dioxide.
State the common air pollutants as
carbon monoxide, sulfur dioxide and
oxides of nitrogen, and describe their
sources.
Explain the presence of oxides of
nitrogen in car exhausts and their
catalytic removal.
Describe the rusting of iron in terms of
a reaction involving air and water, and
simple methods of rust
prevention, including paint and other
coatings to exclude oxygen.

3. How do you know something
is water?
The tests for water – there are TWO things you can do:
1. Add a few drops to white anhydrous
copper(II) sulphate.
• If it turns from white to blue then it’s
water!
2. Dip in a piece of dry blue cobalt chloride
paper.
• If it turns from blue to pink then it’s
water!

4. We need water all the time – how do we purify it?
1. A screen
1
2. A coagulant is added
3. Air is added –
flotation tanks.
Then the sludge is
skimmed off.
4. Sand and other
filters
5. Disinfection with
chlorine or fluorine
6. Storage in
a reservoir
2
3
4
5
6

5. 1. A screen traps any large particles such as
twigs.
2. A coagulant is added – a chemical to make
small suspended particles stick together.
3. Next, air is blown through the water in
flotation tanks, to make the coagulated
particles float to the top. They are
skimmed off.
4. The water is passed through a bed of fine
sand to filter it
• It may go through further filters like
charcoal to remove bad tastes and
smells.
5. Chlorine is added to kill bacteria. Fluorine
can also be added to help fight tooth
decay.
6. The water is pumped to a storage
reservoir, ready for you!

6. Uses of water
– this is not that hard…;)
Water in industry
Water is an important raw material and has many uses. It is used as a solvent and as a
coolant both in the home and in industry. It is used in many important industrial
processes including the manufacture of sulphuric acid.
Seawater/brine is a valuable resource e.g. large scale evaporation in 'salt pans' (using
fuel burning or solar energy) to produce 'sea salt' sodium chloride NaCl, the water also
contains lots of other salts including bromides from which the element bromine is
extracted.
The water cycle.
Water is the most abundant substance on the surface of our planet and is essential for
all life. Water in rivers, lakes and the oceans is evaporated by the heat of the Sun
(endothermic – it absorbs energy thus cooling our planet). The water vapour formed
rises into the atmosphere, cools and forms clouds of condensation (exothermic –
releasing energy). Eventually this gives rain and snow 'precipitation' which on melting
returns to the rivers, seas and oceans.

7. What is in our air?
–again this is not that hard…;)
Clean air is as a mixture of:
• 78% nitrogen
• 21% oxygen
• 1% - small quantities of:
• noble gases
• water vapour
• carbon dioxide.

8. How do you separate
oxygen and nitrogen
from air?
Air is a mixture of gases – they all
have different boiling points!
Start at 3 min
end at 6:30
Boiling points of gases (°C):
• CO2 -32
• O2 -183
• N2 -196
3. Liquefied air is then passed into the bottom
of a fractionating column – the column is
warmer at the bottom.
4. Liquid N2 boils first where it is piped off
5. Liquid O2 collects at the bottom
1. Air is filtered to remove dust
2. Air is cooled in stages until -200°C. During this process:
• H2O condensed and was removed at 0°C
• CO2 freezes at -79°C and is removed
W
A
R
M
E
R

9. ACK! I can’t breath!
Pollutant How is it formed? What harm does it do?
Carbon monoxide
(CO)
colourless gas, insoluble,
no smell
Burning of fossil fuels in too little air
(inside car engine and furnaces)
Poisonous even in small amounts.
Blocks oxygen receptors in
haemoglobin – so you suffocate.
Sulfur dioxide (SO2)
an acid gas with a sharp
smell
Burning of fossil fuels – especially in
power stations
Eye and throat irritant and causes
respiratory problems. Dissolves in
water to form acid rain.
Nitrogen oxides
(NO2 & NO)
acidic gases
Burning of fossil fuels – then a
reaction happens with NOx and O2
Respiratory problems and dissolves
in water to form acid rain.
Lead compounds
Burning of fossil fuels (a long time
ago tetra-ethyl lead was added to gas
– now it is only used in some
countries)
Lead poisoning damages children’s
brains. Damages kidneys and nervous
systems in adults.
AIR POLLUTION!

10. burning less fuel by having more efficient
engines
using low sulfur fuels
using catalytic converters, which convert
nitrogen monoxide to nitrogen and
oxygen, and carbon monoxide to carbon
dioxide
adjusting the balance between public and
private transport, with more people using
buses and trains instead of cars
How do you reduce air
pollution?
Atmospheric pollution caused by the exhaust given out by cars can be
reduced by:
NO & CO
A catalytic converter – you
can find this in your car
N2, O2 &
CO2
in
out
But is CO2 harmless?

11. NO & CO
in N2, O2 &
CO2
out
Why do you think its called a catalytic converter?
Both types consist of a ceramic structure coated with a metal catalyst, usually
platinum, rhodium and/or palladium.
In the catalytic converter, there are two
different types of catalysts at work: a
reduction catalyst and an oxidation
catalyst.
In A: NO is reduced:
2NO(g) → N2(g) + O2(g)
A
In B: CO is oxidised:
2CO(g) + O2(g) → 2CO2(g)
B

12. Rust! – when air and water collide
After several days what will you see?
Place nails in test tubes like this:
Air and water:
Water, no air:
Air, no water:
Rust!
No rust
No rust
Rusting needs oxygen AND water. The iron has been oxidised.
4Fe(s) + 2H2O(l) + 3O2(g) → 2Fe2O3·2H2O(s)
What are some ways to prevent rusting?

13. What are some ways to prevent
rusting?
Cover the iron (to keep out oxygen and water):
• Paint
• Grease
• Another metal (galvanising with zinc, electroplating with tin)
Cover the iron (to keep out oxygen and water):
• Paint
• Grease
• Another metal (galvanising with zinc, electroplating with tin)
Let another metal corrode instead:
Use magnesium or zinc as they are more reactive than iron. This
is called sacrificial protection.

14. The last bit from Stoichiometry…
Use the molar gas volume, takes as 24dm3 at room temperature and
pressure
Calculate stoichiometric reacting masses and reacting volumes of solutions;
solution concentrations will be expressed in mol/dm3 (calculations involving
the idea of limiting reactants may be set)
Fluorine F2
38g
Chlorine Cl2
71g
Oxygen O2
32g
Imagine 3 containers each with a volume of 24dm3
(cubic decimeter) and each is at standard room
temperature and pressure. Standard room temperature
and pressure is SET to 20°C and 1 ATM – which we say
rtp for short – standard room temperature and
pressure.
What do all of
these
containers
have in
common?
They all
contain
1 mole!
1mole 1mole 1mole

15. So we can conclude that 1 mole of every gas occupies the same
volume, at the same temperature and pressure.
At room temperature and pressure this is 24dm3.
This is also called its molar volume.
A
Cloud A has nitrogen
dioxide NO2
B
Cloud B has oxygen O2
Here are two clouds – they have identical volumes and
are at the same temperature and pressure.
Do they also
have the same
number of
moles?
YES!
at rtp it is:
1 mole
How much does each cloud weigh?
Cloud A: NO2 = 46g Cloud B: O2 = 32g

16. Volume at
rtp (dm3)
No. of
moles 24dm3
Use this triangle to help you
with these problems. Cover
the one you need to find out!
Calculating gas volumes from
moles and grams
1. What volume does 0.25 moles
of a gas occupy at rtp?
2. What volume does 22grams of
carbon dioxide gas occupy at
rtp?
1 mole occupies 24dm3 so:
0.25moles occupies 0.25 x 24dm3 = 6dm3
(or 6000cm3) at rtp.
Molar mass of CO2 = 44g/mol so:
22grams = 0.5mole
0.5moles occupies 0.5 x 24dm3 = 12dm3 (or 12000cm3) at rtp.

17. Volume at
rtp (dm3)
No. of
moles 24dm3
Use this triangle to help you
with these problems. Cover
the one you need to find out!
Calculating gas volumes from
equations
1. What volume of hydrogen will react
with 24dm3 of oxygen to form water?
2. When sulfur burns in air it forms sulfur
dioxide. What volume of this gas is
produced when 1g of sulfur burns?
2H2(g) + O2(g) → 2H2O(l) so:
Mole ratio between H2 and O2 is 2:1 therefore
2 x 24dm3 = 48dm3 at rtp.
S(s) + O2(g) → SO2(g) and molar mass of S is 32g/mol so:
1g = how many moles? = 1/32 = 0.031moles of S.
Mole ratio between S and SO2 is 1:1 therefore 0.031moles of SO2
0.031 x 24dm3 = 0.75dm3 at rtp.