Chemistry - Processing Crude Oil (AQA)
Pitch is used to hold small stones together to make roads.

Chemistry - Processing Crude Oil (AQA)

Crude oil and other fuels is one area studied in GCSE Science. This is the fifth of six quizzes on that topic and it looks specifically at two methods of processing crude oil - 'cracking' and 'fractioning'.

Crude oil is formed from the remains of dead sea plants and creatures that became buried in the sediments of the sea floor millions of years ago. Ancient humans used crude oil that they found as 'pitch'. This gathered as pools where oil bearing rocks were exposed at the surface of the Earth. They used this thick and gooey substance for waterproofing their huts and perhaps even on the planks they used to make their boats. Come the modern era things changed. After the discovery was made of how to drill for it, crude oil become one of the most useful resources that we take from the Earth's crust.

Various methods of processing are required before any use can be made of crude oil. Oil straight from the ground is a complex mixture of many thousands of chemical compounds which, when separated, can be used in many ways - as fuels, for making plastics, for making medicines, and much more besides. The pitch used by early humans was processed by natural means - the volatile chemicals evaporated into the air leaving the less volatile chemicals behind as pitch. We still use pitch for making waterproof building materials like roofing felt and for glueing together small stones to make road surfaces.

Mixtures of liquids can be separated by distillation. This works only if the liquids have different boiling points. The chemicals in crude oil have a wide range of boiling points so the process of fractional distillation (or fractioning) is used. This process allows complex mixtures of liquids to be separated because of their different boiling points. To obtain even more useful products from the 'fractions' of oil, some of the chemicals are 'cracked'. Cracking involves using heat and a catalyst, or steam and very high temperatures, to break longer molecules into shorter ones that are more reactive and can be used as polymers.

Take this quiz to test your knowledge of fractioning and cracking, two methods used in the processing of crude oil.

At an oil refinery, how often is oil put into the fractional distillation column?
Once a day
Twice a day
Every hour
All the time
You are expected to know that the process is continuous. The fractionating column at an oil refinery is only 'switched off' if there is a breakdown or if maintenance is required
Crude oil is put into the fractionating column in what form?
As a hot vapour
As a cold vapour
As a hot liquid
As a cold liquid
The crude oil is heated to a temperature where all of the chemicals have boiled and then injected into the fractional distillation column to rise and cool, allowing the different hydrocarbons to condense at different levels
What happens to the chemicals in the crude oil vapour as they rise?
Nothing, they remain vapourised
As they reach an area that is the same temperature as their boiling point they condense
As they reach an area that is the same temperature as their melting point they condense
They react together to form fuels
When they condense, the chemicals form droplets of liquid that fall back down the column onto a collecting tray and can be removed from the fractionating column
Why does fractional distillation of crude oil work?
Because the chemicals in crude oil have the same melting points
Because the chemicals in crude oil boil at different temperatures
Because the chemicals in crude oil have different viscosities
Because the chemicals in crude oil are very volatile
This allows them to be condensed from hot, vapourised crude oil at different places in a fractional distillation column, thus separating the mixture
Which of the following statements best describes the molecules in crude oil?
The molecules in crude oil are not chemically combined
The molecules in crude oil are chemically combined
The molecules in crude oil are all very large
The molecules in crude oil are all very small
There is a wide range of sizes of molecules in crude oil, none of which are chemically combined with each other - crude oil is a mixture
The demand for certain fractions of oil is greater or smaller than the output, for example, there is not enough of the fraction containing the chemicals used as fuel for cars, and there is more of the bitumen fraction than can be used. How is this problem solved?
Some of the gas molecules are joined together to make bigger molecules like petrol and diesel
More roads are built to use up the bitumen fraction
Some of the molecules in the bitumen fraction are cracked
More oil is distilled so that enough of each fraction is made, the unused products are then thrown away
Cracking of larger molecules breaks them down into smaller and more useful molecules which saves having to waste them
Most of the fractions of crude oil are used as what?
About the only fraction not used as a fuel is the bitumen fraction
The chemicals from crude oil are mainly alkanes. Which of the following statements best describes alkanes?
Alkanes are hydrocarbons with sulfur molecules attached
Alkanes are hydrocarbons with multiple bonds between the carbon atoms
Alkanes are hydrocarbons with single bonds between the carbon atoms
Alkanes are hydrocarbons made from carbon atoms alternating with hydrogen and oxygen atoms in a long chain
Hydrocarbons with only single bonds between the carbon atoms are called saturated
Where are the coolest temperatures in the fractionating column?
At the very bottom
Just above the bottom
Somewhere in the middle
At the very top
The column is cooler the higher up you go
Which of the following is not required for cracking?
High temperatures
A catalyst
Large hydrocarbon molecules
Cracking of the long carbon chain alkanes from crude oil produces a shorter carbon chain alkane and an alkene. As well as this 'catalytic' cracking, other methods such as steam cracking are also used
You can find more about this topic by visiting BBC Bitesize - Crude oil, hydrocarbons and alkanes - AQA

Author:  Kev Woodward

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