Revision
C1 C2 C3
Go to C1
Go to C2
Go to C3
C1 - Air Quality
Atmosphere
argon
carbon dioxide
Respiration
(adds carbon dioxide to the atmosphere)
glucose + oxygen  carbon dioxide + water
Photosynthesis
(removes carbon dioxide from the atmosphere)
carbon dioxide + water  glucose + oxygen
Early Earth
The early atmosphere consisted mainly of carbon dioxide and
water vapour (probably from volcanoes), and also some nitrogen
and methane.
On Earth, temperatures began to cool. The water vapour gradually
condensed to form the oceans.
Some of the carbon dioxide began to dissolve in the oceans and
later became incorporated into sedimentary rocks.
Scientists looked at fossil evidence of early life. The evidence
suggests that oxygen levels first increased due to early plant life.
The early plants used up carbon dioxide during photosynthesis and
released oxygen.
The 3 main fossil fuels are:
• coal
• crude oil
• natural gas
The chemical reaction when a fuel burns is:
FUEL + OXYGEN
H
O O
H C H +
O O
H
CARBON
+ WATER
DIOXIDE
H O H
O C O
+
H O H
Incomplete burning produces carbon monoxide
During the course of a chemical reaction the numbers of atoms of
each element must be the same in the products as in the reactants
Atmospheric pollutants cannot just disappear, they have to go somewhere
• particulate carbon is deposited on surfaces, making them dirty;
• sulphur dioxide and nitrogen dioxide react with water and oxygen to
produce acid rain;
• carbon dioxide is used by plants in photosynthesis;
• carbon dioxide dissolves in rain water and in sea water.
How can atmospheric pollution caused by power stations which burn
fossil fuels be reduced ?
• using less electricity;
• removing sulfur from natural gas and fuel oil;
• removing sulfur dioxide and particulates (carbon and ash) from
the flue gases emitted by coal-burning power stations
How can atmospheric pollution caused by exhaust emissions from
motor vehicles be reduced ?
• burning less fuel by having more efficient engines;
• using low sulphur 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;
• having legal limits to emissions (which are enforced by the use of
MOT tests).
Burning of fuel > sulphur dioxide gas > reacts with water vapour > acid rain
(which contains sulfur eg coal)
hydrogen
carbon monoxide
oxygen
sulfur dioxide
sulfur
carbon dioxide
nitrogen
nitrogen monoxide
carbon
nitrogen dioxide
water
Sample
Test 1
Test 2
Test 3
A
35
36
37
B
36
33
35
C
32
26
34
D
35
36
38
Range = lowest value to the highest value
108 / 3
36
outlier
Eg for sample C
including
32 to 34 Not
the outlier
The average / mean is calculated to smooth out small differences in the
data. It is the best estimate of the true value.
When asked to evaluate data, make reference to its reliability (i.e. is
it repeatable ?
Range 2
These ranges do not overlap
so there is a real difference.
Range 1
Range 2
Range 1
These ranges do overlap so
there is not a real difference.
How does air quality affect our health?
To find out what causes hayfever it is important to first look at what
factors (pollen) are linked with hayfever. Factors are variables
that may affect the outcome (hayfever).
If an outcome increases (or decreases) as a particular factor
increases, this is called a correlation.
Evidence shows there is a correlation between pollen levels and
hayfever symptoms, but is pollen the cause of hayfever?
Another correlation is if the concentration of nitrogen dioxide stays
high for several days, there is an increased risk of people with
asthma suffering from asthma attacks – but does nitrogen oxide
cause asthma
Continue with Foundation
Go to Higher
Spend 10 min writing down everything you can remember about C1
oxygen
argon
nitrogen
C


(61+63+65+62+64)  5
63
hydrocarbons
carbon dioxide or water
sulphur dioxide


Go to C1
Go to C2
Go to C3
Higher material
can justify the claim that there is/is not a ‘real difference’
between two measurements of the same quantity;
recall that nitrogen monoxide NO, is formed during the combustion
of fuels in air, and is subsequently oxidised to nitrogen dioxide
NO2 .(NO and NO2 are jointly referred to as ‘NOx’);
can explain why scientists regard it as important that a scientific
claim can be replicated by other scientists;
can explain why a correlation between a factor and an outcome
does not necessarily mean that one causes the other, and can give
an example to illustrate this;
Spend 10 min writing down everything you can remember about C1
hydrocarbons
carbon dioxide or water


E
D
A
B




Acid rain
Go to C1
Go to C2
Go to C3
C2 - Material Choices
Quick Overview
Properties of materials – tensile strength, shear strength,
hardness, flexibility, elasticity, melting point, absorbency
Testing materials – fair test, reliability, accuracy, range,
mean, outlier, real difference
Changing properties of polymers – chain length, density,
cross linking, plasticizers
Natural and synthetic
Life cycle assessment – energy used, materials used,
resources used, effects on the environment
Crude Oil
Properties of materials – tensile strength, shear strength,
hardness, flexibility, elasticity, melting point, absorbency
tensile strength – when trying to pull it
shear strength – when trying to tear it
absorbency – ability to absorb liquid
melting point – temperature at which a solid becomes a liquid
Testing materials – fair test, reliability, accuracy, range,
mean, outlier, real difference
How do you make data more reliable ?
• do repeat measurements
• don’t include outliers
• use mean values
How do you make data more accurate ?
• use more precise instruments
Range 2
Range 2
Range 1
Range 1
These ranges do not overlap
so there is a real difference.
These ranges do overlap so
there is not a real difference.
Key Words
throwing something away
disposal
landfill
burying rubbish
burning rubbish
incineration
can be broken down naturally in the environment
biodegradable
renewable
a source which will not run out
non-renewable
reusable
recyclable
a source which will run out
can be used again (after cleaning) as something useful
can be broken down/melted and be made into something useful
Why is it better to use data rather than opinion in
justifying a position ?
> because it is more convincing to use verifiable evidence
How may a measurement be inaccurate ?
> eg faulty equipment, human error etc
How can several measurements of the same quantity
give different results ?
> the accuracy of the equipment ; the quantity has a
natural variation
What key thing makes data reliable ?
> when it is repeatable
The mean is the best estimate of the true value.
What is an outlier ?
> data which is much higher or lower than all of
the other values
Why are outliers often discarded ?
> because they are usually errors
What is a fair test ?
> when you only change one factor (independent variable)
and control the others by keeping them the same and
then measure the outcome (dependent variable).
The hydrocarbon molecules in crude oil vary in size.
methane
butane
The larger the molecule:
• the greater the number of carbon atoms
• the higher its boiling point
• the less volatile it is
• the less easily it flows ( the more viscous it is )
• the less easily it ignites ( the less flammable it is )
Polymerisation is the joining together of monomers
to make polymers
Polymerisation
using 2 different types of
monomer produces a polymer
with different properties
polymer
monomers
Conditions - Heat & a Catalyst
ethene
polyethene (polythene)
Only a small percentage of crude oil is used for
chemical synthesis, what is the rest of it used for ?
> fuels and lubricants
The petrochemical industry refines crude oil to produce
fuels, lubricants and the raw materials for chemical synthesis
fuel
chemical synthesis
fuel
fuel
fuel
fuel & lubricants
fuel & lubricants
What affects the temperature at which a
substance melts ?
> the greater the strength of the forces between the
particles the higher the amount of energy needed to
break them out of the solid structure
branching
cross linking
high density
B
A
D
C
E
plasticiser
chain length
branching
cross linking
high density
/ crystallinity
plasticisers
chain length
depends on the branching
increases strength, more rigid,
stops molecules sliding past each
other
increases strength, hardness
and density, molecules closer
together
more flexible, easier to bend,
allows molecules to slide past
each other
the longer the stronger
Natural fabrics
wool
plant
cotton
animal
silk
plant
leather
insect
rubber
sheep
Why are mixtures of fabrics often used, eg cotton
and polyester for a shirt ?
> to take advantage of useful properties, eg cotton is
good at absorbing sweat and polyester will make it
more stretchable
Wood versus Plastic !
> wood uses a renewable resource while plastic
involves a non-renewable resource (ie crude oil),
however, wood rots where as plastic doesn’t rot
Nanotechnology – the use and control of structures called
nanoparticles on a tiny (nanometre) scale.
Nanometre –a unit of length 1000000000 times smaller
than a metre
Nanoparticles of a material show different properties to
larger particles of the same material.
Uses of nanotechnology
•Sunscreen
•Tennis balls and rackets
•Electronic paper
•Clothing
•Self-cleaning windows
Continue with Foundation
Go to Higher


x

x

refined
hydrocarbons
x
x

x

x


x


softer
stronger
stronger
x



x

Go to C1
Go to C2
Go to C3
can justify the claim that there is/is not a ‘real
difference’ between two measurements of the same
quantity;
can explain why it is necessary to control all factors
thought likely to affect the outcome other than the
one being investigated, ie can explain a fair test
can explain why different courses of action may be
taken in different social and economic contexts.
4
x
x

x

x


x


softer
x


x


x
x




x




x


x
x


Go to C1
Go to C2
Go to C3
C3 - Chemicals in our
lives: risks and benefits
A journey through geological time
The Earth’s outer layers are divided into a number of tectonic
plates. The plates move because of very slow convection currents
in the underlying solid mantle.
Magnetic clues in rocks help geologists to track the very slow
movement of the continents
Processes such as mountain building, erosion, sedimentation,
dissolving, and evaporation have led to the formation of valuable
minerals.
Clues to the conditions under which rocks were formed come from
fossils, shapes of sand grains, and ripples made by flowing water.
Salt (sodium chloride) – sources and uses
Uses
Sea salt – large-scale
•Preserving food
extraction of salt from
•Processing food
the sea is only economical
•Source of chemicals e.g. chlorine
on coasts with hot and dry
•Treat roads in winter
climates.
Rock salt – contains about 90% sodium chloride in the mineral halite.
Solution mining –salt used for the chemical industry is extracted by
pumping water down into the rock called brine. Salt crystals are recovered
by evaporating the water.
Salt in food –used as flavouring. Eating too much salt can raise
people’s blood pressure, this can increase the risk of developing
heart disease or having a stroke
Alkalis and their uses
Alkalis were needed in pre-industrial times
•To neutralise acid soils
•Convert fats and oils into soap
•Make glass
Traditional sources of
alkalis were
•Burnt wood
•Stale urine
•Make chemicals that bind natural dyes to
cloth
Alkalis are important because they neutralise acids.
Sodium hydroxide + hydrochloric acid  sodium chloride + water
(alkali)
(acid)
(salt)
Hydrochloric acid produces chloride salts
Sulfuric acid produces sulfate salts
Nitric acid produces nitrate salts
Alkaline carbonate + acid  salt + carbon dioxide + water
Making alkali on a large scale
• Leblanc invented a process in 1791 that used chalk, salt
and coal to make the alkali sodium carbonate.
•The Leblanc process was highly polluting.
•Parliament passed the Alkali Acts in 1863 to tackle the
pollution problem.
Benefits and risks of water treatment
Chlorination of drinking water in Britain became increasingly
common in the early 20th century, this led to a steep decline in
deaths from typhoid.
Some scientists are concerned that chlorination can lead to the
formation of trihalomethanes (THMs).
There is a suspicion that THMs could lead to some forms of cancer,
but research studies have not found any firm evidence to support
this idea..
The electrolysis of brine
Manufacturing chemicals from salt by electrolysis needs a lot of energy
Uses of chemicals from salt
Sodium hydroxide
Chlorine
•Make bleach
•Treat drinking water
•Make soap and paper
•Make bleach
•Process food products
•Make HCl
•Remove pollutants from
water
•Make plastics
•Chemical processing and
products
•Make fibres
•Make solvents
Hydrogen
•Make hydrochloric acid
•Fuel to produce steam
Protecting health and the environment
REACH – introduced in 2007 by the EU to collect information about
the hazards of chemicals and to assess the risks.
POPs – persistent organic pollutants. These are organic compounds
that do not break down in the environment for a very long time. They
can spread widely around the world and build up in fatty tissue of
humans and animals. They can be harmful to people and the
environment.
Stages in the life of PVC (synthetic polymer)
Chlorine and ethene are combined to make vinyl chloride (can cause
cancer)
Vinyl chloride molecules are joined to make long chains of PVC
poly(vinyl chloride) by polymerisation
PVC granules are sent to factories to be moulded under heat and
pressure.
About half of PVC is used to make pipes (carry drinking water, sewage
and gas). A softer type is used to make clothing and garden hoses.
The best way to get rid of old PVC is recycling. Some polymer waste
can be burnt in special incinerators. Unfortunately most ends up in
landfill
The properties of PVC can be altered by
plasticisers
Plasticisers added to PVC can leach
out from the plastic into the
surroundings where they may have
harmful effects.
Go to C1
Go to C2
Go to C3