Alcohols (OCR GCSE Chemistry A (Gateway))

Alcohols Structure & Formula

• All alcohols contain the hydroxyl (-OH) functional group which is the part of alcohol molecules that is responsible for their characteristic reactions

• Alcohols are a homologous series of compounds that have the general formula C_nH_2n+1OH

• They differ by one -CH₂ in the molecular formulae from one member to the next

Diagram of the side chain and -OH group in ethanol which characterizes its chemistry

The First Four Alcohols

• The names and structures of the first four alcohols are shown below

• In terms of naming, the same system is used as for alkanes and alkenes, with the final ‘e’ being replaced with ‘ol’

Table showing the Formulae and Structures of the First Four Alcohols

Reactions of Alcohols

• Alcohols are colourless liquids that dissolve in water to form neutral solutions

• The first four alcohols are commonly used as fuels

• School laboratories use ethanol in spirit burners as it burns cleanly and without strong odours

• Methanol and ethanol are also used extensively as solvents

• This is because they can dissolve many substances that water cannot such as fats and oils, but can also dissolve most of the substances that water can

• Alcohols undergo combustion to form carbon dioxide and water

• The complete combustion of ethanol is as follows:

CH₃CH₂OH + 3O₂ → 2CO₂ + 3H₂O

• Alcohols undergo oxidation to produce carboxylic acids, an organic acid

• This is achieved by heating the alcohols with acidified potassium manganate(VII)

  CH₃CH₂OH + 2[O]     →       CH₃COOH  + H₂O

ethanol                         ethanoic acid

• The [O]  is a symbolic representation of an oxidising agent which helps to simplify the equation