The first three members of the alcohols homologous series are all soluble in water.
Solubility decreases as the chain length increase, a larger part of the alcohol molecule is made up of a non-polar hydrocarbon chain: the hydrocarbon chain does not form hydrogen bonds with water molecules. Alcohols can be classified as primary, secondary or tertiary alcohols. This classification depends on the number of alkyl groups attached to the carbon carrying the alcohol group, C-OH. If the alcohol is Primary, this means the -OH group is attached to a carbon atom with no alkyl groups or bonded to one alkyl group.
For example, Methanol and butan-1-ol are both primary alcohols. Methanol has an -OH group attached to a carbon with no alkyl groups. Butan-1-ol has an -OH group attached to a carbon with one CH3CH2CH2-alkyl group. In a secondary alcohol, the -OH group is attached to a carbon atom bonded to two alkyl groups. Propan-2-ol is a secondary alcohol, as it has an -OH group attached to a carbon with two CH3- alkyl groups.
Tertiary alcohol, the -OH group is attached to a carbon atom bonded to three alkyl groups. 2-methylbutan-2-ol is a tertiary alcohol, has an -OH group attached to a carbon with a total of three alkyl groups: two CH3- groups and one CH3CH2- group. In a plentiful supply of oxygen, alcohols burn completely to form carbon dioxide and water. This equation below shows the complete combustion of alcohol. Complete Combustion of alcohols occurs with a clean flame, alcohol + oxygen gas ? carbon dioxide gas + water vapour. Excess O2(g) is present to create the reaction.
The products are CO2(g) and H2O(g). Incomplete Combustion of alcohol, combusts with a smokey or sooty flame due to the production of solid carbon. Reaction is alcohol + oxygen gas ? carbon solid + carbon monoxide gas + water vapour. Insufficient O2(g) is present, that is, there is excess alcohol present meaning O2(g) is the limiting reagent in the reaction. The products are either CO(g) and/or C(s) as well as H2O(g). Combustion of alcohols releases energy making alcohols useful as fuels.