AQA AS Chemistry

Revision Notes

3.5.1 Classifying Alcohols

Classification of Alcohols

  • Primary alcohols are alcohols in which the carbon atom bonded to the -OH group is attached to one other carbon atom (or alkyl group)
  • Secondary alcohols are alcohols in which the carbon atom bonded to the -OH group is attached to two other carbon atoms (or alkyl groups)
  • Tertiary alcohols are alcohols in which the carbon atom bonded to the -OH group is attached to three other carbon atoms (or alkyl groups)

Hydroxy Compounds Classifying Alcohols, downloadable AS & A Level Chemistry revision notes

Classifying primary, secondary and tertiary alcohols and alcohols with more than one alcohol group

  • Only primary and secondary alcohols can get oxidised when mildly oxidised with acidified K2Cr2O7
    • Primary alcohols get mildly oxidised to aldehydes
    • Secondary alcohols get mildly oxidised to ketones
  • Tertiary alcohols do not undergo oxidation with acidified K2Cr2O7
  • Therefore, only the oxidation of primary and secondary alcohols will change the colour of K2Cr2O7 solution as the orange Cr2O72- ions are reduced to green Cr3+ ions

Hydroxy Compounds Tests Alcohols, downloadable AS & A Level Chemistry revision notes

Only primary and secondary alcohols can be oxidised, turning the orange solution green
No colour change is observed with a tertiary alcohol

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