Chemistry C1 4.2 Fractional distillation.

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How is crude oil separated into fractions?
Using fractional distillation.
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What do the properties of each fraction depend on?
The size of the hydrocarbon molecules.
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What do fractions with lower boiling points have in common?
They are less viscous and burn more easily (very flammable and easy to ignite), they also burn with clean flames and produce little smoke which makes them very useful as fuels.
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How is simple distillation done?
In steps by heating the mixture to different temperatures.
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How is fractional distillation done?
Continuously by vaporising the mixture and condensing the fractions at different temperatures.
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How does the size of the hydrocarbon molecule affect its boiling point?
The larger the molecule, the higher the boiling point of the hydrocarbon.
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What is the first thing to happen during fractional distillation?
The crude oil is vaporised and fed into a fractionating column (a tall tower that is hot at the bottom and gets cooler going up the column).
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What happens once the vaporised crude oil is fed into a fractionating column?
There are many trays with holes to allow gases through, as vapours move up the column they get cooler, they hydrocarbons condense to liquids when they reach the level that is at their boiling point.
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What happens when the vapours reach the level that is at their boiling point?
Different liquids collect on the trays at different levels and there are outlets to collect the fractions.
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Why are hydrocarbons with the smallest molecules collected?
They have the lowest boiling point so are collected at the top of the column, and those with the highest boiling points are collected at the bottom.
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Why are different hydrocarbons collected at different levels of a fractional distillation column?
Different hydrocarbons have different boiling points so they condense at different levels.
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What properties would you expect for a fraction that is collected one-third of the way up a fractionating column?
Medium-high boiling point (about 250 degrees celsius) quite viscous/oily/thick liquid, not very flammable, burns with quite a smoky flame.
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**LOOK UP DIAGRAMS OF FRACTIONAL DISTILLATION**
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Other cards in this set

Card 2

Front

What do the properties of each fraction depend on?

Back

The size of the hydrocarbon molecules.

Card 3

Front

What do fractions with lower boiling points have in common?

Back

Preview of the front of card 3

Card 4

Front

How is simple distillation done?

Back

Preview of the front of card 4

Card 5

Front

How is fractional distillation done?

Back

Preview of the front of card 5
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