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Basics of hydrocarbons for AQA GCSE Chemistry

Basics of hydrocarbons

This page covers the following topics:

1. Hydrocarbons
2. Homologous series
3. Saturated compounds

Hydrocarbons are molecules containing only carbon and hydrogen, they are named according to the number of carbons present.

Hydrocarbons

A homologous series is a group of hydrocarbons which all have the same general formula, an example of this is all alkanes have the general formula CnH2n+2 where 'n' is the number of carbons in the chain. Physical properties of molecules change up a homologous series.

Homologous series

When all carbon atoms are bonded to four different atoms, a molecule is considered saturated. Sometimes a carbon atom is only bonded to three different molecules and a double bond forms between two carbon atoms, this is an unsaturated molecule.

Saturated compounds

1

Why do unsaturated molecules decolourise bromine water?

The carbon-carbon double bond opens up and the carbons form a bond with the bromine atoms. When the bromine is removed from the water it loses its brown colour.

Why do unsaturated molecules decolourise bromine water?

2

What does the name of the compound CHโ‚„ start with?

meth

What does the name of the compound CHโ‚„ start with?

3

What will the name of the compound Cโ‚„Hโ‚โ‚€ start with?

but

What will the name of the compound Cโ‚„Hโ‚โ‚€ start with?

4

Is the boiling point of a long chained molecule higher or lower than the boiling point of a shorter molecule from the same homologous series?

The boiling point of a long chained molecule is higher.

Is the boiling point of a long chained molecule higher or lower than the boiling point of a shorter molecule from the same homologous series?

5

Are long or short chain molecules from the same homogenous series more volatile?

Short chain molecules are more volatile.

Are long or short chain molecules from the same homogenous series more volatile?

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