General formulae
4 marks · NormalEach member of a homologous series contains the same functional group. The alcohol series contains the functional group –OH.
Describe, with an example, what is meant by a functional group.
Explain why all alcohols undergo similar chemical reactions.
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(a) A functional group is an atom or group of atoms responsible for the chemical properties of a compound. For example, the –OH group in alcohols. · must show definition, example: –OH group
(b) All alcohols have the same –OH functional group, so they react in similar ways. · must show same functional group, similar chemical reactions
Common mistakes: Not providing an example of a functional group; Omitting reference to chemical properties
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Marking points
B1 (a) · 1 mark · Describes functional group as atom/group that gives compound its chemical properties.
B2 (a) · 1 mark · Provides a correct example, such as –OH in alcohols or C=C in alkenes.
B3 (b) · 1 mark · States all alcohols have the same functional group.
B4 (b) · 1 mark · Links this to similar chemical reactions or properties.
Worked solution
a) A functional group is an atom or group of atoms responsible for the characteristic chemical properties of a compound. For example, the –OH group in alcohols is the functional group.
b) All alcohols contain the same –OH functional group, so they undergo similar chemical reactions because this group controls how they react.