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Chemistry - Crude Oil (AQA)
One of the ways we can extract oil which is trapped underground is by drilling from an oil rig.

Chemistry - Crude Oil (AQA)

One of the topics covered in GCSE Science is the chemistry of crude oil and other fuels. This is the first if six quizzes on that subject and it looks in particular at the hydrocarbons and alkanes which are found in crude oil.

Crude oil formed over a long period of time - millions of years in fact. It formed from the remains of dead sea creatures and plants that rotted down anaerobically (with little or no oxygen) as they became buried with sediments on ancient sea beds. The oil is trapped underground by layers of impermeable rocks and is extracted from the ground by drilling oil wells.

But what is the chemistry of crude oil? Well, it is a mixture of thousands of different chemicals which are mainly hydrocarbons. These are covalently bonded molecules made mainly from the elements hydrogen and carbon, in fact, most are only made from those two elements and are that is why they are called hydrocarbons.

The main types of hydrocarbon in crude oil come from the family of chemicals known as the alkanes - for example, octane, an important component of the petrol that we use as fuel for cars. The larger alkanes with carbon chain lengths of over 35 atoms are soft solids and are used in the construction industry for roofing and roads.

Crude oil is also always associated with another fossil fuel, gas, because some of the molecules of the alkane family are very small. Small covalently bonded molecules are often gases at room temperature. Natural gas is methane, the simplest alkane, and it is piped from the oil fields of the north sea to homes and businesses all over Britain.

But chemistry allows us to use crude oil for more than just fuel. There is more bitumen than can be used. To save throwing it away, it can be 'cracked'. This involves using heat and catalysts to break down the longer carbon chains into smaller molecules, including petroleum and molecules like ethene, which can be used to make plastics.

Crude oil is a mixture of what?
Two or more elements or compounds not chemically combined together
Two or more elements or compounds chemically combined together
Hydrocarbons combined together with water and gas
Mainly alkanes
The chemical properties of each substance in the mixture are unchanged. It is possible to separate the substances in a mixture by physical methods
What are hydrocarbons?
Long chain molecules made from water and carbon
Short chain molecules made from water and carbon
Chemicals made from hydrogen and carbon chemically joined together
A food group that provides energy
The hydrogen and carbon are covalently bonded. The carbon can be a single atom (for example, methane) or can be arranged as a chain (for example, octane has eight carbon atoms joined together in a chain)
Which of the following best describes most of the hydrocarbons in crude oil?
Saturated means that there are no double bonds in the molecule
Which of the following best describes the saturated hydrocarbons in oil?
You should be able to recognise alkanes from their formulae (drawn or written) but you only need to know the names of the first four - methane, ethane, propane and butane - for the exam
The formula of any alkane can be worked out from which of the following?
The letter 'n' represents the number of carbon atoms so an alkane with 20 carbon atoms would have 42 hydrogen atoms
How are the different hydrocarbons separated from crude oil?
Fractional distillation
Separating funnel
This is so-called because the crude oil is separated into fractions
Which of the following lists contains the words missing from the following passage in the correct order?

The many __________ in crude oil may be separated into fractions by ___________ the oil and allowing it to condense at a number of different ___________. This process is ___________ distillation.
temperatures, evaporating, hydrocarbons, fractional
hydrocarbons, evaporating, temperatures, fractional
chemicals, evaporating, hydrocarbons, fractional
fuels, heating, places, evaporating
This is the first step to converting crude oil into useful products
Which of the following best describes the smaller hydrocarbons when compared to large hydrocarbons?
The smaller hydrocarbons are more viscous
The smaller hydrocarbons are less flammable
The smaller hydrocarbons are more volatile
The smaller hydrocarbons produce more soot when they burn
The smallest molecules from fractional distillation of crude oil are so volatile that they are gases at ordinary temperatures
The process of breaking down of the larger hydrocarbons to smaller, more useful chemicals is called what?
Cracking is carried out using heat and a catalyst
Crude oil is made from alkanes. During cracking what other type of hydrocarbon is produced and how is it different from the alkanes?
Ethene is produced and it is colourless
Alkyne is produced and it is odourless.
Alcohol is produced and it is inflammable
Alkene is produced and it has a double covalent bond
Cracking of a long chain alkane produces a shorter chain alkane and an alkene. The characteristic of an alkene is that it has at least one double bond between two adjacent carbon atoms
You can find more about this topic by visiting BBC Bitesize - Crude oil, hydrocarbons and alkanes - AQA

Author:  Kev Woodward

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