AQA Chenistry 1A CRUDE OIL

AQA chemistry crude oils

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Fuels from crude oil

1.Crude oil provides important chemicals: we use to make electricity, fuel our cars, warm our homes. Crude Oil is a MIXTURE of many different compounds that boil at different temperaturesunder different conditions so to be useful it needs to be separated to make useful fuels.

2.We can separate mixtures of liquids by DISTILLATION.(heat to boiling, collect vapour, cool and condense) Simple distillation of crude oil can produce liquids that boil within different temperature ranges. 3.Most of the compounds in crude oil are hydrocarbons. This means they contain Carbon and Hydrogen ONLY

4.Many of these hydrocarbons are ALKANES(eg Propane, Ethane,Butane) with the general formula CnH2n+2.( ie double the number of Calcium atoms and add 2 to get the number of Hydrogen atoms! ) Alkanes contain as many hydrogen atoms as possible in each molecule and so we call them SATURATED hydrocarbons.

5.Molecules can be represented by:a) A molecular formula that shows the number of each type of atom or b) A structural formula that shows how the atoms are bonded together.



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Fractional distillation

1.Crude oil is separated at refineries by fractional distillation.This is a contunuous process. There are different kinds of crude oil (eg "light crude" contains more short chain hydro carbons, lighter fractions make better fuels.)

2.The crude oil is vaporised and fed into a fractioning column. This is a tall tower that is hot at the bottom and cooler on the top.                                              3.Inside the column there are many trays with holes to allow gases through. The vapours move up the column and condense on the trays when they reach their boiling points.There are outlets at different levels to collect the liquid fractions.

4.The properties of hydrocarbons depend upon the size and chain length of their molecules. This afffects:Boiling point, Volatility, Viscosity,Flammability.

5.Eg:The hydrocarbons with the smallest molecules have the lowest boiling points and so are collected at the top of the tower. The fractions collected at the bottom have the highest boiling points,they cool to form thick liquids or solids at room temp..Fractions with low boiling points burn more easily, which makes them more useful as fuels.

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Burning fuels

1.When pure hydrocarbons burn completely in plenty of air, they produce:

eg Propane + Oxygen ----> Carbon Dioxide + Water                                                C3H8 + 5O2 ---->3CO2 + 4H2O

2. CONDITIONS matter: fuels we use are not always burnt completely  - INCOMPLETE COMBUSTION - and they may also contain other substances.

3.In a limited supply of air, such as IN AN ENGINE, Carbon Monoxide & Carbon may also be produced, and some of the Hydrocarbons may not burn. - Carbon Monoxide is a poisonous gas ,red blood cells carry it around in your blood instead of oxygen. - Nitrogen and Oxygen in air can also react to make nitrous oxides. They are poisonous & can trigger asthma, also cause acid rain

4.Carbon & unburnt hydrocarbons from tiny particles in the air.These particulates circulate in the air,believed they could damage cells. Especially in Diesel engines which burn hydrocarbons with bigger molecules.                5.Most fossil fuels contain sulphur compounds.When the fuel burns these sulfur compounds produce SULPHUR DIOXIDE.This compound is poisonous and ACIDIC. It is bad for the environment because it is the cause of acid rain.Can also cause engine corrosion.

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Cleaner Fuels

1.The products from burning fossil fuels are released into the atmosphere in exhaust gases.

2.Carbon dioxide is a greenhouse gas. It reduces the amount of heat lost from the earth and causes global warming.Particulates cause health problems and cause global dimming by reflecting sunlight away from the earth.

3.Sulfur dioxide dissolves in water and forms acid rain. The amount of sulfur dioxide released can be reduced by removing sulfur compounds from fuels at the refinery, or by removing sulfur dioxide from the waste gases after burning.

4.Fossil fuels are being used up and will run out in the future.

5.Plants can provide sugars to make ethanol, Adding the ethanol to petrol creates gasohol. This reduces the amount of oil needed and produces less pollution as it burns more cleanly than petrol.OR plants can producduce oils that can be used as biodiesel. This would help global warming as plants take in CO2 & this cancels out the effect of the CO2 from burning them. 6. Another alternative would be burning rubbish in incinerators to heat homes.BUT it is feared harmful dioxins may be produced.

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