Chemistry

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  • Created by: anthony
  • Created on: 28-01-13 19:38
Crude oil is a mixture of compounds called hydrocarbons.
It can be separated into different fractions using fractional distillation and some of these can be used as fuels.
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there are environmental consequences when fossil fuels such as crude oil and its products are used.
Most of the compounds in crude oil are hydrocarbons. This means that they only contain hydrogen and carbon atoms, joined together by chemical bonds. There are different types of hydrocarbon, but most of the ones in crude oil are alkanes.
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The alkanes are a family of hydrocarbons that share the same general formula. This is: CnH2n+2 The general formula means that the number of hydrogen atoms in an alkane is double the number of carbon atoms, plus two.
For example, methane is CH4 and ethane is C2H6. Alkane molecules can be represented by displayed formulae in which each atom is shown as its symbol (C or H) and the chemical bonds between them by a straight line.
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Alkanes are saturated hydrocarbons. This means that their carbon atoms are joined to each other by single bonds.
This makes them relatively unreactive, apart from their reaction with oxygen in the air, which we call burning or combustion.
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Distillation is a process that can be used to separate a pure liquid from a mixture of liquids. It works when the liquids have different boiling points. Distillation is commonly used to separate ethanol (the alcohol in alcoholic drinks) from water.
Distillation process separate ethanol from water drawn in diagram
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Complete combustion Fuels burn when they react with oxygen in the air. The hydrogen in hydrocarbons is oxidised to water (remember that water, H2O, is an oxide of hydrogen).
If there is plenty of air, we get complete combustion and the carbon in hydrocarbons is oxidised to carbon dioxide: hydrocarbon + oxygen → water + carbon dioxide
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The test to show carbon dioxide is limewater it turns from clear to cloudy in the presence of carbon dioxide.
Incomplete combustion If there is insufficient air for complete combustion, we get carbon monoxide. Particles of carbon, seen as soot or smoke, are also released.
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Sulfur Most hydrocarbon fuels naturally contain some sulfur compounds. When the fuel burns, the sulfur it contains is oxidised to sulfur dioxide.
The combustion of a fuel may release several gases into the atmosphere, including: -water vapour -carbon dioxide -carbon monoxide -particles -sulfur dioxide These products may be harmful to the environment.
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The fossil fuels include coal, oil and natural gas. Various factors need to be considered when deciding how to use a fossil fuel.
These include: -the energy value of the fuel in J/g of fuel -the availability of the fuel how the fuel can be stored the cost of the fuel the toxicity of the fuel - whether it is poisonous any pollution caused when the fuel is used, such as acid rain
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In general, solids such as coal are easier to store than liquids and gases. But they are often more difficult to light. Liquids and gases ignite more easily. They also flow, which means they can be transported through pipelines.
Sulfur dioxide is produced when fuels that contain sulfur compounds burn. It is a gas with a sharp, choking smell. When sulfur dioxide dissolves in water droplets in clouds it makes the rain more acidic than normal This is called acid rain.
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Acid rain reacts with metals and rocks such as limestone. Buildings and statues are damaged as a result
Sulfur dioxide can be removed from waste gases after combustion of the fuel. This happens in power stations.
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Sulfur can be removed from fuels at the oil refinery. This makes the fuel more expensive to produce, but it prevents sulfur dioxide being produced
Carbon dioxide from burning fuels causes global warming, a process capable of changing the world’s climate significantly.
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Other cards in this set

Card 2

Front

Most of the compounds in crude oil are hydrocarbons. This means that they only contain hydrogen and carbon atoms, joined together by chemical bonds. There are different types of hydrocarbon, but most of the ones in crude oil are alkanes.

Back

there are environmental consequences when fossil fuels such as crude oil and its products are used.

Card 3

Front

For example, methane is CH4 and ethane is C2H6. Alkane molecules can be represented by displayed formulae in which each atom is shown as its symbol (C or H) and the chemical bonds between them by a straight line.

Back

Preview of the back of card 3

Card 4

Front

This makes them relatively unreactive, apart from their reaction with oxygen in the air, which we call burning or combustion.

Back

Preview of the back of card 4

Card 5

Front

Distillation process separate ethanol from water drawn in diagram

Back

Preview of the back of card 5
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