New
New
Year 11
OCR
Higher

Cracking fractions of crude oil

I can describe the uses of different fractions of crude oil and describe what cracking is and how it is used to produce lighter fractions that are in greater demand.

New
New
Year 11
OCR
Higher

Cracking fractions of crude oil

I can describe the uses of different fractions of crude oil and describe what cracking is and how it is used to produce lighter fractions that are in greater demand.

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Lesson details

Key learning points

  1. Fractions of crude oil have different properties and uses, affecting the demand for these molecules.
  2. Larger hydrocarbons can be broken down (cracked) to produce smaller, more useful molecules.
  3. Cracking can be done by various methods including catalytic cracking and steam cracking.
  4. The products of cracking include alkanes and alkenes, which have a double bond between two carbon atoms.
  5. Bromine water changes from orange/brown to colourless in the presence of an alkene.

Keywords

  • Cracking - Cracking is a thermal decomposition reaction where larger alkanes are broken down into smaller alkanes and alkenes.

  • Thermal decomposition - A thermal decomposition reaction is a type of reaction that uses heat to break down a reactant compound into two or more products.

  • Catalyst - A catalyst is a chemical that speeds up the rate of a reaction without itself being used up.

  • Saturated - Alkanes are saturated hydrocarbons as they contain only single bonds between carbon atoms.

  • Unsaturated - Unsaturated compounds contain at least one carbon-carbon double covalent bond.

Common misconception

Cracking is the same as fractional distillation.

Fractional distillation separates hydrocarbons based on their boiling points. Cracking alters the molecular formula of compounds.

A teacher demonstration showing the cracking of paraffin could be performed.
Teacher tip

Licence

This content is © Oak National Academy Limited (2024), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

Lesson video

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6 Questions

Q1.
Which property of hydrocarbons affects their viscosity?
boiling point
Correct answer: molecular size
flammability
solubility
Q2.
In the fractional distillation of crude oil, which fraction is collected at the bottom of the column?
petroleum gases
kerosene
diesel
heavy fuel oil
Correct answer: bitumen
Q3.
Which of the following statements about alkanes are true?
Correct answer: Alkanes are hydrocarbons.
Correct answer: Alkanes contain single bonds between carbon atoms.
Ethane is the simplest alkane.
Alkanes contain double bonds between carbon atoms.
Q4.
Which of the following hydrocarbons is the most flammable?
Correct answer: methane
ethane
propane
butane
Q5.
What is fractional distillation?
A process to separate a mixture of solids based on their densities.
Correct answer: A technique to separate a mixture of liquids based on their boiling points.
A method to combine different liquids into a single mixture.
A process to break down large alkanes into smaller more useful molecules.
Q6.
Why do smaller hydrocarbon molecules have lower boiling points?
Correct answer: they have fewer intermolecular forces
they have more intermolecular forces
they are more viscous
they are more flammable

6 Questions

Q1.
Which of the following fractions are commonly used as fuels for cars?
Correct answer: petrol
bitumen
liquified petroleum gas
Correct answer: diesel
kerosene
Q2.
What is the name of the thermal decomposition reaction where larger alkanes are broken down into smaller alkanes and alkenes?
Correct Answer: cracking
Q3.
Which of the following is an example of a hydrocarbon that can be cracked?
methane
ethene
propene
Correct answer: butane
Q4.
Which process involves heating larger alkanes to vapourise them, mixing with steam and heating to high temperatures to break down the hydrocarbon molecules?
Correct answer: cracking
neutralisation
simple distillation
fractional distillation
Q5.
Which of the following statements about alkenes is false?
They have a double bond between carbon atoms.
They are unsaturated hydrocarbons.
They react with bromine water.
Correct answer: Bromine water remains an orange/brown colour when an alkene is added.
Q6.
Which statement best describes why different fractions of crude oil have different properties and uses?
They have the same boiling points but different densities.
Correct answer: They have different boiling points, viscosities, and flammabilities.
They have the same chemical structure but different colours.
They have the same boiling point.