Fractional Distillation of Crude Oil Flashcards

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What is crude oil?

Crude oil is a thick, dark liquid that is a mixture of many different hydrocarbons, mainly alkanes.

Why do we need to separate crude oil?

We separate crude oil because it is not very useful as a whole mixture, but its different parts (fractions) are useful as different fuels and materials.

What is meant by fractional distillation of crude oil?

Fractional distillation is the process that separates crude oil into different fractions based on their different boiling points.

What is a fraction in fractional distillation?

A fraction is a group of hydrocarbons from crude oil that have similar numbers of carbon atoms and similar boiling points.

Why is crude oil heated before it enters the fractionating column?

Crude oil is heated so that most of it boils and turns into vapour, which can then rise up the fractionating column.

How does the temperature change from the bottom to the top of a fractionating column?

The bottom of the fractionating column is very hot, and it gets cooler towards the top.

How does fractional distillation separate hydrocarbons with different boiling points?

Hydrocarbon vapours rise up the column and cool; each type condenses back to a liquid at the height where the temperature is just below its boiling point, so they are collected in separate trays.

Where do long-chain hydrocarbons condense in the fractionating column compared to short-chain hydrocarbons, and why?

Long-chain hydrocarbons have higher boiling points, so they condense near the hot bottom of the column; short-chain hydrocarbons have lower boiling points, so they condense higher up where it is cooler.

Name three fractions obtained from crude oil by fractional distillation, from lowest boiling point to higher boiling point.

From low to higher boiling point: gases, petrol (gasoline), kerosene, then diesel, fuel oil and bitumen.

Is fractional distillation of crude oil a physical or a chemical change, and why?

It is a physical change because it only separates the hydrocarbons; the molecules themselves do not change or react.