C1, C2, C3 OCR Nationals

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C1- Air quality
C1.1 Which chemicals make up air, and which ones are pollutants? How do I make
sense of data about air pollution?
The Earth is surrounded by a thin layer of gasses called the ATMOSPHERE. It is about 15km thick.
Air forms part of the atmosphere - it is a mixture of different gases consisting of small molecules
with large spaces between them.
The amount of water vapour and polluting gases varies as a result of human activity or by natural
processes (e.g. volcanoes). Many of these gases affect the quality of the air we breathe. Gases
released in one part of the world will gradually spread through the atmosphere and can affect the
air quality of people miles away.
THE EARTHS EARLY ATMOSPHERE
Since the formation of the Earth, 4.6 billion years ago, the atmosphere has changed a lot.
The earliest atmosphere contained ammonia, water vapour and carbon dioxide. These
gases came from inside the Earth and were often released through the action of
volcanoes.
As the temperature of the planet fell, the water vapour in the air condensed to form
oceans and seas.
The evolution of photosynthesising organisms started to reduce the amount of carbon
dioxide and increase the amount of oxygen in the atmosphere.
Carbon from carbon dioxide in the air was removed from the atmosphere by dissolving in
the oceans and then became locked up in sedimentary rocks as carbonates and fossil fuels.
NOW: Clean air contains about 78% nitrogen, 21% oxygen and 1% other gasses including
0.035% carbon dioxide.
Normal air contains varying amounts of water vapour and some polluting gases.

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Human activity has changed the composition of the atmosphere by adding small amounts of
carbon monoxide, nitrogen oxides and sulphur dioxide to the atmosphere AND extra carbon
dioxide and small particles of solids (e.g. carbon) to the atmosphere.
POLLUTANTS that harm the environment can also harm humans indirectly. For example:
Acid raid makes the water in rivers and lakes to acidic for plants and animals to survive This has
a direct impact on our food chain and natural resources like trees.
Pollutant Harmful to ...…read more

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WEATHER: pollutants are mixed up and carried around by the winds. Wind can move the
pollutants many miles and even carry them from one country to another.
C1.2 What chemical reactions produce air pollutants? What happens to these
pollutants in the atmosphere?
Many atmospheric pollutants are made by the burning of fossil fuels. This happens in power
stations and in the engines of vehicles.
POWER STATIONS: Most power stations are fuelled by either coal or natural gas.…read more

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Incomplete combustion occurs in car engines, so exhaust emissions contain carbon particulates
and carbon monoxide, as well as carbon dioxide. Many samples of coal contain sulfur, so is
released into the atmosphere when fuels that contain sulfur compounds burn to create SULFUR
DIOXIDE.…read more

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Making sure cars are fitted with CATALYTIC CONVERTERS which reduce the amount of
carbon monoxide and nitrogen monoxide emitted.…read more

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CATALYTIC CONVERTER
Global Choices National Choices Local Choices Personal Choices
In 1997 there was an Some initiatives set by Many local authorities · Using less energy in the
international meeting the UK: are trying to encourage home reduces the
about climate change in · Setting legal limits for us to make demand for energy from
Kyoto, Japan. People vehicle exhaust environmentally friendly power stations. E.g.…read more

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C2 ­ Material Choices
C2.1 How do we measure the properties of materials and why are the results useful?
Different materials behave in different ways because they have different PROPERTIES. Solid
materials can differ in one or more of the following ways:
Melting point
Strength in tension (when pulled)
Strength in compression (when pushed)
Stiffness
Hardness
Density
Many of the products that we use are made using PLASTICS, RUBBERS and FIBRES. The
SUTABILITY of a material to a particular job depends on its properties.…read more

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RUBBER is also waterproof and flexible; it is very hard-wearing, and will not slip easily when in
contact with the ground.
Many people may have ideas about why materials have different properties, but these opinions
are not very useful if they are not supported by DATA. To justify an explanation, you need to have
data to support it, This data may be obtained by taking measurements.
For Example: A supermarket needs to produce carrier bags. It can use either polythene or
biodegradable plastic.…read more

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When extracted CRUDE OIL is a thick, black sticky liquid however is not very useful until it has
been processed at an oil refinery. The process of refining involves separating the hydrocarbons
into fractions or batches using a technique called FRACTIONAL DISTILLATION. Each fraction
separates as they have different boiling points. The crude oil is heated in a furnace to around
400°C. This allows all of the hydrocarbons in the crude oil to move into the bottom of the
fractionating tower.…read more

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Polychloroethen Unreactive, does
Chloroethene Window frames Wood
e (PVC) not rot
C2.3 Why does it help to know about the molecular structure of materials such as
plastics and fibres?
MOLECULAR STRUCTURE OF MATERIALS
It is possible to produce a wide range of different polymers with properties that make them suited
to a particular use. The properties of solid materials depend on how the particles in these
materials are arranged and how they are held together.…read more

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