What is crude oil?

Crude oil is a mixture of hydrocarbons, primarily alkanes.


It is a fossil fuel formed from ancient organic matter.

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What is the name of the process we use to separate the components of crude oil?

Fractional distillation

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What physical property of hydrocarbons allows them to be separated by fractional distillation?

The different boiling points of hydrocarbons.

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Outline the process of fractional distillation.

  1. Crude oil is heated to vaporise it into a gas and then passed into the fractionating column.
  2. The fractionating column is cooler at the top compared to the bottom. As the gas rises up the column, it gradually cools down.
  3. When the individual hydrocarbon components in the gas mixture reach a height where the temperature is lower than their respective boiling points, they condense into liquids.
  4. These liquids are collected in trays placed at specific intervals along the column and are drawn off as separate fractions.

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What are the names and uses of crude oil fractions?

The names and uses of some crude oil fractions are:

  1. Petrol is used as a fuel for vehicles.
  2. Naptha is used as as petrochemical feedstock.
  3. Kerosene is used as jet fuel.
  4. Diesel is used as a fuel for vehicles.
  5. Mineral oil is used as a lubricant.
  6. Bitumen is used in road surfacing.


There are several more crude oil fractions which haven't been included in this list.

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What is meant by the term fraction, in the context of fractional distillation?

A fraction is a mixture of hydrocarbons with similar boiling points.

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How do the boiling points of hydrocarbons change as you move down the fractionating tower?

The boiling points of hydrocarbons increase as you move down the fractionating tower.

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What happens to the temperature as you move higher up the fractionating tower?

The temperature decreases as you move higher up the fractionating column.


The temperature is cooler towards the top of the fractionating tower.

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Give 3 physical properties of short-chain hydrocarbons.

Physical properties of short-chain hydrocarbons include:

  1. Low boiling points (they are typically gases or volatile liquids).
  2. High flammability.
  3. Low viscosity.

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Give 3 physical properties of long-chain hydrocarbons.

Physical properties of long-chain hydrocarbons include:

  1. High boiling points.
  2. Low flammability.
  3. High viscosity (they are often in the form of thick residues like tar or bitumen).

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Are hydrocarbons with long or short chains collected at the top of the fractionating column?

Hydrocarbons with shorter chains are collected at the top of the fractionating column.

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Do hydrocarbons with long or short chains have a lower boiling point?

Hydrocarbons with shorter chains have lower boiling points.

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Why do short-chain hydrocarbons make good fuels?

They are very flammable and volatile, so are easy to combust for energy. 

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Why are long-chain hydrocarbons bad fuels?

They are not very flammable or volatile. This means they are hard to combust for energy.

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