Alcohols (OCR Gateway GCSE Chemistry)

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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 CnH2n+1OH
  • They differ by one -CH2 in the molecular formulae from one member to the next

Alcohol- Functional Group, IGCSE & GCSE Chemistry revision notes

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

Alcohols table, IGCSE & GCSE Chemistry revision notes

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

Examiner Tip

It is standard practice to write the functional group on the end as it shows what the molecule is. E.g. methanol is CH3OH, not CH4O.

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Stewart

Author: Stewart

Expertise: Chemistry Lead

Stewart has been an enthusiastic GCSE, IGCSE, A Level and IB teacher for more than 30 years in the UK as well as overseas, and has also been an examiner for IB and A Level. As a long-standing Head of Science, Stewart brings a wealth of experience to creating Exam Questions and revision materials for Save My Exams. Stewart specialises in Chemistry, but has also taught Physics and Environmental Systems and Societies.