Crude oil contains a mixture of hydrocarbons that can be separated using fractional distillation. Shorter hydrocarbon molecules have fewer intermolecular bonds, resulting in lower boiling points and condensing at the top of the distillation column. Longer hydrocarbon molecules have higher boiling points due to more intermolecular bonds and condense at the bottom. However, the longer molecules have high viscosity making them less useful. Through a process called cracking, longer hydrocarbons are broken down by heating and passing over a catalyst, resulting in smaller alkanes and alkenes, which have a double carbon bond. Both alkanes and alkenes are useful hydrocarbons obtained through cracking crude oil.

1. Crude oil
Fractional distillation
hydrocarbons
Cracking
Alkanes
Alkenes

2. Crude oil
Crude oil is formed from the buried remains of plants
and animals.
Over millions of years with high temp and pressure,
the remains turn into crude oil.
Crude oil Is a mixture of hydrocarbons. Hydrocarbons
are fuels that are made of just oxygen and carbon.
Because it’s a mixture, the different hydrocarbon
molecules are not chemically bonded together.. So
they keep all their original properties such as their
condensing points.
This means that crude oil can be split up into separate
fractions by fractional distillation.

3. Fractional distillation
The fractionating column works continuously,
with heated crude oil piped in at the bottom. The
vaporised oil rises up to the column and the
various fractions are constantly tapped off at the
different levels where they condense.

4. This is crude oil. It’s a
mixture of
hydrocarbons. This
isn't useful therefore
we must separate the
hydrocarbons.
First you heat
the crude oil to
350 degrees

5. The shorter hydrocarbons
Condense at the top. The
Longer hydrocarbons condense
At the bottom. Can you think why?
This is because long chained hydro-
Carbons have loads of
intermolecular bonds. Therefore
they have a high melting
and boiling point
Short chained molecules have
Fewer intermolecular bonds
So they have a low melting and
Boiling point.

6. Their properties
• Molecules with SHORT Carbon chains have a
LOW boiling point. They also have LOW
VICSOSITY.
• Molecules with LONG carbon chains have a
HIGH boiling point. They also have HIGH
VISCOSITY.
High viscosity means it doesnt flow as
smoothly/easily. – its more gloopy and less runny.

7. Properties
Short chained hydrocarbons burn easily.
Long chained hydrocarbons
are difficult to burn..
They end up giving a
very Smokey flame.

8. What do we get from fractional
distillation

9. Alkanes
• Crude oil is mostly alkanes. Alkanes are made up
of carbon and hydrogen atoms. Different alkanes
have chains of different lengths
• The first four alkanes:
MethANE

10. Alkanes
• Crude oil is mostly alkanes. Alkanes are made up
of carbon and hydrogen atoms. Different alkanes
have chains of different lengths
• The first four alkanes:
EthANE

11. And the pattern continues
Remember it like this:
Monkeys
Eat
Peanut
Butter
Alkanes are saturated
hydrocarbons- this means
the carbon atom bonds with
as many hydrogen atoms as
it can.
The line shows a covalent
bond

12. Crude oil may run out..
• Most scientists think that oil might run out. But
no one knows exactly when. Some people think
we should immediately stop using oil for things
like transport when there are alternatives. So
however long oil lasts for it’s a good thing to
start conserving it and finding alternatives.

13. Not the environments best friend..
• Oil spills can happen as the is being transported.
Birds get covered in the oil and are poisened
when they try to clean themselves.
• You have to burn oil to release the energy from
it. but burning oil is thought to be a major cause
of global warming, acid rain and global
dimming.

14. Cracking crude oil
• Cracking means splitting up long chained
hydrocarbons.
• Long chained hydrocarbons have a high
viscosity. They're more gloopy. Therefore theyre
not that useful. Products of cracking are more
useful.

15. Cracking….
• Cracking is a thermal decomposition reaction-
breaking down a molecule by heating them.
• First you heat the long chained hydrocarbon and
vaporise It.
• The vapour is then passed over a powdered
catalyst. The long chain molecules split apart “
or crack “. Most of the products from cracking
are alkanes and alkenes

16. Alkenes?
• Alkenes are very useful. They have a c=c double
bond. They're hydrocarbons with a double bond
between TWO of their carbon atoms.
• The formula for alkenes : CnH2n

17. In summary..
Crude oil contains a mixture of hydrcarbons
These hydrocarbons have their own original
preporties including their condensing point.
Fractional distilatin seperates all the
hydrocarbons. The short molecules go to the top
of the column because they have a low boiling
point- this is because there are less intermolecular
bonds. Long chained molecules have a high
viscosity – they're more gloopy.

18. In summary..
Because they're more gloopy they're not that
useful. Therefore you heat them up and pass them
over a catalyst. This is known as cracking and you
get a smaller alkane and you get an alkene.
Alkenes have a double bond and alkanes are
saturated. Both alkanes and alkenes are
hydrocarbons that are useful.

19. Exam
question: