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Alkanes for SQA National 5 Chemistry

Alkanes

This page covers the following topics:

1. Formulae and solubility of alkanes
2. First four alkanes
3. Molecular formula of alkanes
4. Nomenclature of alkanes

Alkanes are saturated hydrocarbons, they are non-polar so are insoluble in water.

Formulae and solubility of alkanes

The first 4 alkanes follow the usual naming pattern for hydrocarbons.

First four alkanes

Molecular formula shows the number and type of atoms present in a molecule, remember that for alkanes they will follow the general formula from before.

Molecular formula of alkanes

When naming branched hydrocarbons you must count the number of carbons in the longest carbon chain, this is the name of the alkane, and add the names of the branches to the start of the name with a number to indicate which carbon they come off of. The molecule shown is 2-methylbutane using these rules.

Nomenclature of alkanes

1

How does solubility of alkanes change with chain length?

Shorter alkanes are slightly more soluble than longer chain alkanes.

How does solubility of alkanes change with chain length?

2

Draw the molecule 2,3-dimethylheptane.

image

Draw the molecule 2,3-dimethylheptane.

3

What is the name of the molecule Cโ‚‚Hโ‚†?

ethane

What is the name of the molecule Cโ‚‚Hโ‚†?

4

What is the general formula of alkanes?

CnH2n+2

What is the general formula of alkanes?

5

What is the molecular formula of ethane?

Cโ‚‚Hโ‚†

What is the molecular formula of ethane?

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