GCSE Chemistry

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Alkanes

Alkanes are a family of hydrocarbons. They are made up of chains of carbon atoms surrounded by hydrogen atoms. Alkanes only contain single covalent bonds. The alkane family contains molecules that look similar but have different length chains of carbon atoms.

The first four alkanes are:

Methane which has the molecular formula CH4; Ethane which is C2H6; Propane is C3H8 and Butane which is C4H10.

Reactions

Alkanes burn to produce carbon dioxide and water provided there is plenty of oxygen around.

Alkanes do not react with most chemicals

They do not react with aqueous reagents (substances dissolved in water).

Alkanes do not react because they CC bonds and CH bonds in them do not react.

Alcohols

Alcohols all contain the functional group OH. Because all alcohols have this all alcohols have similar properties.

The first alcohol is called methanol and the molecular formula is CH2OH and ethanol is C2H5OH.

You need to know how alcohols compare with water and alkanes in terms of their physical properties.

1) Ethanol is soluble in water. Alkanes are not.

2) Ethanol and water are both good solvents-meaning lots of things dissolve in them. The boiling point of ethanol is 78 degrees centigrade. This is lower than the boiling point of water but much higher than the boiling point of a similar size alkane e.g. ethane has a boiling point of minus 103 degrees centigrade.

3) Ethanol is a liquid at room temperature. It evaporates easily and gives off fumes (it is volatile). Methane and ethane are also volatile but are gases at room temperature. Water is liquid at room temperature but not volatile.

Industry

Alcohols such as methanol and ethanol can dissolve lots of compounds that water can’t e.g. hydrocarbon and oils. This makes them very useful solvents in industry. Methanol is also used in industry as a starting point for making other organic chemicals. Ethanol is used in perfumes and aftershave lotions as it can mix with both the oils and the water.

Methylated spirit is ethanol with chemicals (e.g. methanol) added to it. It is used to clean paint brushes and as a fuel.

Reactions

Alcohols burn is air because they contain hydrocarbon chains. Pure ethanol is clean burning so it is sometimes mixed with petrol and used as fuel for cars to conserve crude oil.

Sodium reacts gently with ethanol to produce sodium ethoxide and hydrogen. Sodium reacts much more vigorously with water-often melting because of the

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