Chemistry-C1

C1.1 Which chemicals make up air?

The atmosphere (air) that surrounds the Earth is made up mainly of nitrogen, oxygen and argon, plus small amounts of water vapour, carbon dioxide and other gases.
Air is a mixture of different gases consisting of small molecules with large spaces between them.
The relative proportions of the main gases in the atmosphere are approximately 78% nitrogen, 21% oxygen and 1% argon.
Other gases or particulates may be released into the atmosphere by human activity or by natural processes (eg volcanoes), and that these can affect air quality.
The Earth’s early atmosphere was probably formed by volcanic activity and consisted mainly of carbon dioxide and water vapour.
Water vapour condensed to form the oceans when the Earth cooled.
The evolution of photosynthesising organisms added oxygen to, and removed carbon dioxide from, the atmosphere.
Carbon dioxide was removed from the atmosphere by dissolving in the oceans and then forming sedimentary rocks, and by the formation of fossil fuels.

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Human activity has changed the composition of the atmosphere by adding: a) small amounts of carbon monoxide, nitrogen oxides and sulfur dioxide to the atmosphere. b) extra carbon dioxide and small particles of solids (eg carbon) to the atmosphere.
Some of these substances, called pollutants, are directly harmful to humans (eg carbon monoxide reduces the amount of oxygen that blood can carry), and that some are harmful to the environment and so cause harm to humans indirectly (eg sulfur dioxide causes acid rain).

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coal is mainly carbon
diesel fuel and fuel oil are mainly compounds of hydrogen and carbon (such molecules of carbon and hydrogen atoms are called hydrocarbons).
when fuels burn, atoms of carbon and/or hydrogen from the fuel combine with atoms of oxygen from the air to produce carbon dioxide and/or water (hydrogen oxide)
a substance chemically combining with oxygen is an example of oxidation, that loss of oxygen is an example of reduction, and that combustion reactions therefore involve oxidation
fuels burn more rapidly in pure oxygen than in air
oxygen can be obtained from the atmosphere and can be used to support combustion (eg in oxy-fuel welding torches)
in a chemical reaction the properties of the reactants and products are different
atoms are rearranged during a chemical reaction
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, thus conserving mass (Law of Conservation of Mass).
sulfur dioxide is produced if the fuel that is burned contains any sulfur

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burning fossil fuels in power stations and for transport pollutes the atmosphere with: a) carbon dioxide and sulfur dioxide b) carbon monoxide and particulate carbon (from incomplete burning) c) nitrogen oxides formed from the reaction between atmospheric nitrogen and oxygen at the high temperatures inside engines.

the formulae for carbon dioxide CO₂, carbon monoxide CO, sulfur dioxide SO₂, nitrogen monoxide NO, nitrogen dioxide NO₂ and water H₂O to visual representations of their molecules.

atmospheric pollutants cannot just disappear, they have to go somewhere e.g. a) particulate carbon is deposited on surfaces, making them dirty, b) sulfur dioxide and nitrogen dioxide react with water and oxygen to produce acid rain which is harmful to the environment, c) carbon dioxide is used by plants in photosynthesis, d) carbon dioxide dissolves in rain water and in sea water.

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atmospheric pollution caused by power stations that burn fossil fuels can be reduced by: a) using less electricity b) removing sulfur from natural gas and fuel oil c) removing sulfur dioxide and particulates from the flue gases emitted by coal-burning power stations.
the only way of producing less carbon dioxide is to burn less fossil fuels.
atmospheric pollution caused by exhaust emissions from motor vehicles can be reduced by: a) burning less fuel, for example by having more efficient engines b) using low sulfur fuels c) using catalytic converters (in which nitrogen monoxide is reduced to nitrogen by loss of oxygen, and carbon monoxide is oxidised to carbon dioxide by gain of oxygen) d) adjusting the balance between public and private transport e) having legal limits to exhaust emissions (which are enforced by the use of MOT tests)

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