Chemistry - Key Stage 4
Organic Chemistry
Fractional distillation
Miss Mason
Fractional distillation
Intermolecular forces
Fractionating column
Uses of hydrocarbons
Outcome: describe the process of fractional
distillation and the uses of each of the fractions
from this
2
Recap
1. What is crude oil?
Crude oil is a f______ f____ made from the remains of a_______ b_______ (mainly
p________) buried in mud. It is a m_______ made up of mainly h_____________.
2. Identify and draw the first 4 alkanes.
3. Work out the formula of an alkane that has 12 carbon atoms.
3
Recap
1. What is crude oil?
Crude oil is a fossil fuel made from the remains of ancient biomass (mainly plankton) buried in mud. It is a mixture
made up of mainly hydrocarbons.
2. Identify and draw the first 4 alkanes.
Methane Ethane Propane Butane
[Wikimedia Commons] - [Wikimedia Commons] - [Ethan Lewis] [Wikimedia Commons] - [Propan [Wikimedia Commons] - [Butan Lewis]
[Methan Lewis] - Methane-2D- - Ethane-2D-flat Lewis] - Propane-2D-flat - Butane-2D-flat
square
3. Work out the formula of an alkane that has 12 carbon atoms.
CnH2n+2 C12H26
4
Fractional distillation
[Wikimedia Commons] - [Luigi Chiesa] -
Colonne distillazione
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Hydrocarbons
Longer molecule = stronger intermolecular forces = higher melting and boiling point
Intermolecular force 2 methane molecules
(short chain)
2 propane molecules
(long chain)
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Quick fire question
What is the name we give to the process that separates out the
different compounds from crude oil?
Fractional distillation
Quick fire question
Name the piece of equipment/machinery needed to carry out
fractional distillation.
Fractionating column
Quick fire question
Name the forces that hold hydrocarbon molecules together.
Intermolecular forces
Quick fire question
What happens to the strength of the intermolecular forces in
hydrocarbon molecules with increasing chain length?
Intermolecular forces
become stronger
Quick fire question
What effect do weaker intermolecular forces have on melting and
boiling point?
Lower melting and boiling point
Copy and complete
Fractional distillation is used to…
To carry this out, a f___________ c_______ has to be used.
The hydrocarbons are separated out based on their c_____ l______ as this determines their
m________ and b________ point due to the strength of the i______________ forces.
Longer molecules have stronger i_____________ forces, so require more ________ to break
them down and therefore have a higher m_________ and b_______ point.
Shorter molecules, on the other hand...
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Copy and complete
Fractional distillation is used to extract or separate out the compounds that make up a crude oil mixture.
To carry this out, a fractionating column has to be used.
The hydrocarbons are separated out based on their chain length as this determines their melting and boiling point due
to the strength of the intermolecular forces.
Longer molecules have stronger intermolecular forces, so require more energy to break them down and therefore
have a higher melting and boiling point.
Shorter molecules, on the other hand have weaker intermolecular forces, so require less energy to break them
down and therefore have a lower melting and boiling point.
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Fractionating column
Small molecules
Fraction = mixture of Gas
hydrocarbons with similar <20°C Lower temperature
boiling points Petrol
20-70°C
Naphtha
70-160°C
Kerosene
160-250°C
Diesel
250-350°C
Bitumen
Large molecules
>350°C
Heated crude oil High temperature
Image source: Miss Mason
400°C
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Quick fire question
What is a ‘fraction’?
Mixture of hydrocarbons with a similar
boiling point
Quick fire question
In a fractionating column, where are the highest temperatures?
At the bottom of the column
Quick fire question
In a fractionating column, where do the smallest molecules separate
out?
At the top of the column
Quick fire question
In fractional distillation, what are the fractions separated based on?
Their boiling points
Fractionating column
What does each letter G
<20°C
represent?
F
20-70°C
70-160°C E
160-250°C D
250-350°C
C
B
>350°C
A Image source: Miss Mason
400°C
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Fractionating column
Gas
<20°C
Petrol
20-70°C
Naphtha
70-160°C
Kerosene
160-250°C
Diesel
250-350°C
Bitumen
>350°C
Heated crude oil
Image source: Miss Mason
400°C
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Uses of hydrocarbons
1. Petrol
a) Manufacture of chemicals
2. Naphtha
b) Used for laying roads
3. Kerosene
c) Fuel for cars
4. Diesel
5. Bitumen d) Fuel for aircrafts
e) Fuel for cars, vans and lorries
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Knowledge check!
1. What is the link between chain length and boiling point?
2. Explain the above relationship.
3. Where is the fractionating column the hottest/coldest?
4. What happens at the top of the fractionating column?
5. What happens at the bottom of the fractionating column?
6. How can the fractions naphtha, kerosene and bitumen from crude oil be used?
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1. What is the link between chain length and boiling point?
The longer the chain length, the higher the boiling point.
2. Explain the above relationship.
Longer chains have stronger intermolecular forces so more energy is needed to overcome these.
3. Where is the fractionating column the hottest/coldest?
Hottest at the bottom and coldest at the top.
4. What happens at the top of the fractionating column?
Fractions with the lowest boiling points condense (short-chain hydrocarbons).
5. What happens at the bottom of the fractionating column?
Fractions with the highest boiling points condense (long-chain hydrocarbons).
6. How can the fractions naphtha, kerosene and bitumen from crude oil be used?
Naphtha is used in the manufacture of chemicals.
Kerosene is used as a fuel for aircrafts.
Bitumen is used for laying roads.
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Pause the video to complete your task
Exam-style question
Describe and explain how the fractions are separated in a fractionating
column
You must include information on:
- Chain length
- Intermolecular forces
- Changes of state (e.g. boiling/condensing)
Fractional distillation is used to separate the mixture of hydrocarbons in crude oil based
on their...
Resume once you’re finished
Exam-style question
Describe and explain how the fractions are separated in a fractionating column
● Crude oil is a mixture which is heated until it vaporises
● It is pumped into a fractionating column which is hot at the bottom and cooler at the top
● Vapour rises through the column
● The different hydrocarbon vapours condense when their temperature falls below their boiling point
● Hydrocarbons with low boiling points are collected at the top of the column - these are shorter chain
hydrocarbons with weaker intermolecular forces
● Hydrocarbons with high boiling points are collected at the bottom of the column - these are longer chain
hydrocarbons with stronger intermolecular forces
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Now complete the exit quiz
