C1- Chemistry- C4.1 - 4.5 (Crude Oil and Fuels)

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Fuels from Crude Oil

Key Points

  • Crude oil is a mixture of hydrocarbons
  • A mixture consists of two or more elements not chemically bonded together
  • Hydrocarbons are fuels such as petrol and disel. They are made of just hydrogen and carbon
  • Alkanes are saturated hydrocarbons. They contain as many hydrogen atoms as possible in their molecules.


Crude Oil

  • Crude oil straight from the ground is no use. Its just a lot of substances with different boiling points
  • Therefore, before use we must seperate it into different substances with similar boiling points
  • These are known as fractions. Because the properties of the substances do not change when they are mixed, we can seperate them by 'Fractional Distillation'
  • This seperates the liquids by their boiling points
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Fractional Distillation

Key Points

  • We seperate crude oil into fractions using fractional distillation
  • The properties of each fraction depend on the size of their hydrocarbon molecules
  • Lighter fractions make better fuels as they ignite more easily and burn well, with cleaner (less smoky) flames
  • The boiling point of a hydrocarbon depends on the size of its molecules.
  • The more carbon atoms, the higher the boiling point


Properties and uses of Crude Oil

  • The shorter the molecules, the more runny the hydorcarbon is-(Less viscous) Gloopy
  • The shorter the molecule the more volatile they are- Meaning they turn into a gas at lower tempratures 
  • The shorter the molecules the more flammable the hydrocarbon is
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Burning Fuels

Key Points

  • When we burn hydrocarbon fuels in plenty of air the carbon and hydrogen are completley oxidised. They produce carbon dioxide and water
  • Sulphur impurities in fuels burn to form sulfur dioxide which can cause acid rain
  • Changing the conditions in which we burn hydrocarbon fuels can change the products made
  • In insufficient oxygen, we get poisonous carbon monoxide gas formed. (Incomplete combustion) We can also get particulates of carbon (soot) and unburnt hydrocarbons, especially if the fuel is disel
  • At high tempratures in engines, nitrogen from the air reacts with oxygen to form nitrogen oxides. These cause breathing problems and can cause acid rain
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Using Crude Oil as a Fuel

Crude oil provides an important fuel for modern life

  • Crude oil fractions burn cleanly- meaning good fuels
  • Modern transport is fuled by crude oil- Boats, cars, planes. Also burned in central heating systems and power stations
  • Massive industry of scientists trying to find reserves. We also use crude oil for plastics and chemicals
  • Alternatives- Electricty by nuclear power, wind power, ethanol-powered cars (biodisel)- Solar power
  • However, things are set up for using oil fractions- Peterol/ Disel pumps- filling stations all over the country
  • Crude oil, more reliable than solar/ wind (wont work in certain weather conditions)


Might run out one day

  • Non-renewable
  • We need to develop alternatives- renewable source- wind, solar, tidal power
  • We should start conserving and finding alternatives now! We could only have oil for 25 years
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Environmental Problems

Increasing carbon dioxide causes climate change

  • The level of Co2 is increasing due to the large amounts of fossil fuels humans burn (Enhanced greenhouse effect)
  • This has caused the average temprature of the earth to increase (global warming)
  • Climate change could change rainfall patterns. Also could cause flooding due to melting polar ice caps


Particles cause Global Dimming

  • 25% less sunlight has been reaching the surface compared to 50 years ago (Global dimming)
  • They think this is due to particles of soot and ash that are produced when fossil fuels are burnt. These particles reflect light back into space or produce more clouds that reflect light back into space
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Alternative Fuels

Key Points

  • Biofuels are a renewable source of energy that could be used to replace fossil fuels
  • Biodisel can be made from vegetable oils
  • Ethanol is also a biofuel as it can be made from the sugar in plants
  • Hydrogen is a potential fuel for the future



PROS- Biodisel is carbon neutral. Engines do not need conversion. Produces much less sulpher dioxide and particulates than ordinary petrol and disel

CONS- We cant make enough to replace disel. It is expensive and could increase food prices

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Alternative Fuels (Continued)


  • Can be produced from plant material so is known as a biofuel. Made by fermentation of plants and is used to power cars in some places. It is often mixed with petrol


PROS- Carbon neutral. Only other product is water

CONS- Engines need to be converted before being able to work with ethanol fuels. Ethanol fuel isnt widely avaliable. Worries that as demand increases farmers will stop growing crops and grow ethanol- increasing food prices

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