Crude Oil - AQA GCSE Core

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  • Created on: 03-01-12 11:46
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Crude oil:
It is a dark smelly liquid which is a mixture of different substances.
Crude oil straight out of the ground is not much use because there are too many different
substances in it, all with different boiling points.
Hydrocarbons:
Most the compounds in crude oil are made from hydrogen and carbon. Theses are called
hydrocarbons and are alkanes. This means they have carboncarbon single bonds.
The general formula for this is: CnH2n+2.
Eg: Methane = CH4, Ethane = C2H6, Propane = C3H8 ect...
Alkanes are saturated hydrocarbon which means they contain as many hydrogen atoms as
possible and you can't add any more.
Some hydrocarbons are small (short carbon chain) and others are larger (long carbon chains). The
properties of hydrocarbons depend on the length of their chain.
The smaller the chain, the lower the boiling point, higher the volatility (tendency to turn into a gas),
the more easily it flows (viscosity) and the
more easily it ignites.
Fractional distillation:
To separate out the different substances we
use fractional distillation. The crude oil is
evaporated and its vapours allowed to
condense at different temperatures in the
fractionating column. Each fraction contains
hydrocarbon molecules with a similar number
of carbon atoms.
In the fractionating column, crude oil is fed in
at the bottom. The tower is kept very hot
near the bottom but cooler at the top. The
gases condense when they reach their boiling
point and the different factions are collected
at the different levels.
Burning fuels:
When hydrocarbons burn with plenty of
oxygen, they produce carbon dioxide and
water.
Propane + Oxygen Carbon Dioxide +
Water
C3H8 + 5O2 3CO2 + 4H2O
We can test for water by using Anhydrous Copper Sulphate because it turns from white to blue.
We can test for carbon dioxide by running it through lime water because it turns it milky.
In hydrocarbons there are Sulphur impurities, which react with the Oxygen when burnt to form
Sulphur Dioxide.
Sulphur Dioxide is poisonous and acidic so is a cause of acid rain.
When hydrocarbons are burnt in a car engine, sometimes there isn't enough Oxygen inside the
cylinders. This is called incomplete combustion and carbon monoxide is also produced.
Carbon monoxide is very poisonous because it stops oxygen getting to your cells.
The high temp in the engine allows nitrogen and oxygen to react together to form nitrogen oxide
which are also poisonous and can trigger asthma.
Diesel engines burn longer hydrocarbon molecules. When these big molecules react with Oxygen,
they don't always burn completely so tiny particles of carbon are released into the air. Supposedly
this can cause global dimming or breathing problems.

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Cleaner fuels:
Catalytic converters are put in cars to reduce the amount of pollution given off by cars.
They work by passing the exhaust gases over transition metals. These are arranged in a way so
they have a very large surface area and this cause the nitrogen oxides and carbon monoxide to
react.
Carbon monoxide + nitrogen oxide carbon dioxide + nitrogen
In power stations, sulphur dioxide is removed from the flue gases by reacting it with quicklime.
The devices used are called `scrubbers'.…read more

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