Chemistry GCSE AQA Grade 9 Unit 7: Organic Chemistry notes made by Grade 9 student, now studying A level Chemistry. Includes all relevant details adhering to the specification and visual aids, such as diagrams, pictures, coloured notes, etc.. Similar quality notes available for all units for each t...
Unit 7: Organic Chemistry
Crude Oil, Hydrocarbons and Alkanes
Crude oil is…
Formed over millions of years from fossilised remains of plants and animals (plankton)
Found in porous rocks in the Earth’s crust
A finite resource used as fuel and to produce other chemicals e.g. those making plastics.
Most compounds in crude oil are hydrocarbons.
Hydrocarbons
- Molecules made up of hydrogen and carbon atoms only (hydrocarbons)
- These molecules vary in size, affecting properties and their use as fuels, the larger they are:
The more viscous it is
The higher its boiling point
The less volatile it is
The less easily it ignites
Alkanes
Alkanes = chains of hydrocarbons with C atoms linked to four other atoms.
Alkanes are described as saturated hydrocarbons:
- No more hydrogen atoms can be added.
- Saturated means ‘full-up’
The general formula is C n H 2 n+ 2
Cannot conduct electricity because they are molecular compounds with no charged ions.
React with oxygen in combustion reactions (highly exothermic) making them great fuels.
NAME NO. OF C ATOMS NO. OF H FORMULA STRUCTURE
ATOMS
methane 1 4 CH4
ethane 2 6 C2H6
propane 3 8 C3H8
butane 4 10 C4H10
Homologous series: the members have the same functional group, so they react in a similar way.
Functional group: the part of a molecule that gives it its characteristic properties.
Fractional Distillation
, Crude oil is separated into different fractions using fractional distillation.
How it works:
1. The crude oil is heated until it evaporates.
2. The vapour moves up the fractionating column.
3. The top of the column is much colder than the bottom.
4. Shorter hydrocarbons with lower boiling points reach the top of the fractionating
column before condensing.
5. Longer hydrocarbons with higher boiling points condense at higher temperatures,
because they have higher boiling points, and are collected at the bottom.
6. Fractional distillation works because the different substances in the mixture have
different boiling points.
Refinery gases - e.g.
liquefied petroleum gas
(LPG), propane and butane
for bottled gases
25˚C
Fractionating Column The fractions with low
boiling points rise to
the top of the column.
Gasoline (petrol)
- fuel for cars
Short-chain hydrocarbons 70˚C
Kerosene (paraffin)-
Fractions with different fuel for jet airplanes
boiling points condense at
260˚C
different levels of the column
and can be collected.
Diesel oil (gas oil)- fuel for cars
300˚C and large vehicles
Long-chain hydrocarbons
Heavy fuel oil - fuel oil for
The fractions with high boiling 360˚C generating electricity and for
marine diesel engines
Crude oil vapour points condense and are
collected at the bottom of the
column.
Over 400˚C
Bitumen - to
make roads
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