Objectives:
To revise fractional distillation.
To explain why large hydrocarbons are cracked.
Outcomes:
All of you will be able to explain what is meant by
fractional distillation.
Most of you will be able to explain why cracking is
carried out.
Some of you will be able to recognise an alkene
from a structural or molecular formulae.
Revision – Fractional Distillation
13.09.10
Starter:
List all the fuels you think you have used so far
today and how you have used them e.g.
1) Gas – cooking breakfast.
Where is it found?
What is it used for?
Crude oil
What is it?
What is it made up of?
Small molecules
Big molecules
Medium
molecules
Fuel gas
Naphtha
Diesel
Petrol
Kerosine
Fuel Oil and bitumen
Fuel gas
Burned in the refinery to fuel the distillation process,
sold as LPG, purified and sold as bottled camping gas.
Petrol/ gasoline. Fuel for cars and motorcycles, also used to make
chemicals.
Naphtha
Used to make chemicals.
Paraffin/
Kerosine
Fuel for greenhouse heaters and jet engines,
manufacture of chemicals.
Diesel Fuel
Fuel for lorries, trains.
Fuel/
Lubricating
oil
Fuel for the heating systems of large buildings, fuel for
ships, lubricating oil.
Bitumen
Roofing, and road surfaces.
Fractional distillation
Crude oil can be separated by fractional distillation. The oil is evaporated
and the hydrocarbon chains of different lengths condense at different
temperatures:
Fractions with
low boiling
points condense
at the top
Fractions with
high boiling
points condense
at the bottom
Long chain molecules.
Short chain molecules
Does not flow very well as they
are very thick.
Flows easily (they are quite
thin).
They are less flammable (do not
set on fire).
Are flammable (will set on
fire).
Less volatile (does not turn into a
gas).
Quite volatile (will evaporate).
Have a high boiling point.
Have Low boiling points.
Cracking
Shorter chain hydrocarbons are in greater demand because
they burn easier. They can be made from long chain
hydrocarbons by “cracking”:
Butane
Ethane
For example, this bond
can be “cracked” to give
two of these:
Ethane
Making Hydrocarbons.
1)
2)
3)
4)
5)
6)
Decane C10H22
Butane C4H10
Pentane C5H12
Ethane C2H6
Propene C3H6.
Ethene C2H4.
Which is a correct statement about crude oil?
A. A mixture of carbohydrates.
B. Formed by the decay of dead sea
creatures.
C. Consist of a mixture of very large
molecules.
D. Is purified in an oil rig.
Which is a correct statement about fractional
distillation?
A. Oil is separated into fractions with the same
size molecule.
B. Oil is separated into fractions with the same
density.
C. Oil is separated into fractions with similar
size molecules.
D. Oil is separated into alkanes and alkenes.
Which is a correct order for these fractions
working down from the top of the column?
A.
B.
C.
D.
Fuel gas, kerosine, petrol, diesel, bitumen.
Fuel gas, diesel, kerosine, petrol, bitumen.
Fuel gas, petrol, diesel, kerosine, bitumen.
Fuel gas, petrol, kerosine, diesel, bitumen.
Which of these is a true statement about the
changes that occur as hydrocarbon molecules
get larger?
A.Boiling point decreases.
B.Viscosity increases.
C.Flammability increases.
D.Transparency increases.
Which of these is an alkane?
A. C6H14
B. C4H8
C. C12H24
D. C102H204
Which of these is a true statement about
alkenes?
A. They turn bromine water from colourless to
red
B. They contain a double bond
C. The smallest alkene has 1 carbon atom
D. They have names that end in “ane.”