Crude oil and fuels


Fuels from crude oil

Crude oil is a mixture of many different compounds.

Fractional distillation is used to separate mixtures of liquids.

Most of the compounds in crude oil are hydrocarbons (they contain only hydrogen and carbon).

Alkanes are saturated hydrocarbons.

Alkanes have the general formula CnH2n+2 and do not contain any double bonds.

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Fractional distillation

Crude oil is separated into fractions using fractional distillation.

The properties of each fraction depend on the size of the hydrocarbon molecule.

Fractions with the lowest boiling point and smallest hydrocarbon molecules are collected at the top.
These are very viscous and flammable.

Fractions with the highest boiling points are collected at the bottom.

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Burning fuels

Burning hydrocarbons in plenty of air produces carbon dioxide and water.

Burning hydrocarbons in a limited supply of air (incomplete combustion) may produce carbon monoxide and solid particles and unburnt hydrocarbons (particulates).

Any sulfur compound in the fuel burn to produce sulfur dioxide.

Nitrogen oxides are formed when fuels burn under extreme conditions.

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Cleaner fuels

Many scientists believe that carbon dioxide from burning fuels causes global warming.

Sulfur dioxide and nitrogen oxides cause acid rain.

Particulates cause global dimming.

Pollutants can be removed from waste gases after the fuel is burnt.

Sulfur can be removed from fuels before they are burned so less sulfur dioxide is given off

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Alternative fuels

Biodiesel can be made from vegetable oils.

Biofuels are a renewable source of energy that could be used instead of fossil fuels.

There are advantages and disadvantages of using biodiesel. eg. It requires lots of farmland. But it does not contribute to carbon dioxide levels.

Ethanol is made from sugar and is a biofuel.

Hydrogen is a potential fuel for the future. 

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Cracking hydrocarbons

Hydrocarbon molecules can be broken down by heating them with steam to a very high temperature or by passing their vapours over a hot catalyst. This is called cracking.

Cracking produces alkanes and alkenes.

Alkenes are unsaturated hydrocarbons with the general formula of CnH2n.

Alkenes have a double bond which makes them more reactive. They turn bromine water from orange to colourless.

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Making polymers from alkenes

Plastics are made out of polymers.

Polymers are large molecules made when many small molecules (monomers) join together. 

The reaction to make a polymer is called polymerisation.

Alkenes can be used to make polymers such as poly(ethene) and poly(propene).

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New and useful polymers

New polymers are being developed all the time.

Polymers are designed to have properties that make them specially suited for certain uses.

We are now recycling more plastics and finding more uses for them.

Shape-memory polymers change back to their original shape when temperature or other conditions are changed.

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Plastic waste

Non-biodegradable plastics cause unsightly rubbish, can harm wildlife and take up space in landfill sites.

Biodegradable plastics are decomposed by the action of microorganisms in the soil.

Making plastics with starch granules in their structure helps the microorganisms break down a plastic.

We can make biodegradable plastics from plant material, such as cornstarch.

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Ethanol can be made by fermenting sugar using enzymes in yeast.

Ethanol can also be made by hydration of ethene with steam in the presense of a catalyst.

Using etehen to make ethanol needs non-renewable crude oil. 

Fermentation uses renewable plant material.

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Atoms, elements and compounds

All substances are made of atoms.

Elements are made of only one type of atom.

Compounds contain more than one element.

Atoms have a nucleus surrounded by electrons.

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Atomic structure

The nucleus of an atom is made of protons (postive) and neutrons (neutral). Electrons have a negative charge.

The atomic number (or proton number) is equal to the number of protons in the nucleus.

Elements are arranged in order of their atomic number in the periodic table.

The mass number is the sum of protons and neutrons in the nucleus of an atom.

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The arrangement of electrons in atoms

The atoms of the unreactive noble gases all have very stable arrangements of electrons.

Electrons in atoms are in energy levels that can be represented by shells.

Electrons in the lowest energy level are in the shell closest to the nucleus.

All the elements in the same group of periodic table have the same number of electrons in their outer shell. 

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Forming bonds

Compounds of metals bonded to non-metals have ionic bonds.

The formula of an ionic compounds shows the simpliest ratio of ions.

Compounds of non-metals have covalent bonds.

The formula of a molecule shows the number of atoms in the molecule.

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Chemical equations

Atoms get re-arranged in chemical reactions.

The mass of the products is equal to the mass of the reactants.

Symbol equations should always be balanced. 

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Extracting metals

Metals are usually found in the Earth's crust. They are often combined chemically with other elements such as oxygen.

An ore contains enough metal to make it worth extracting the metal.

The method we use to extract a metal depends on its reactivity. 

The oxides of metals less reactive than carbon can be reduced using carbon.

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Iron and steels

Iron oxide is reduced in a blast furnace to make iron.

Iron from the blast furnace is too brittle for many uses. It has few uses as cast iron.

Most iron is converted intp alloys called steels.

Steels contain carefully controlled quantities of carbon and other elements. 

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Aluminium and titanium

Aluminium and titanium resist corrosion. They also have low densities compared with other strong metals.

Aluminium and titanium cannot be extracted from their oxides using carbon.

It has to be extracted by electrolysis of molten aluminium oxide.

Aluminium and titanium are expensive because extracting them involves many stages and requires large amounts of energy.

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Extracting copper

Most copper is extracted from copper-rich ores by smelting.

Copper can be purified by electrolysis.

Bioleaching and phytomining are new ways to extract copper from low-grade ores. They are used to save the energy needed to extract it from its ore.

Copper can be obtained from solutions of copper salts by displacement of electrolysis. 

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