Chemguide: Support for CIE A level Chemistry

34.2: Phenylamine and azo compounds

Learning outcome 34.2.3

In terms of the number of times it is asked in exams, this statement is really important. It compares the base strengths (the basicity) of ammonia, ethylamine and phenylamine.

Ethylamine is taken as typical of amines in which the amino group is attached to a carbon chain. Phenylamine is typical of those in which the amino group is attached directly to a benzene ring.

This is explained on the page about organic bases.

You will find that the page mainly talks about methylamine rather than ethylamine. It makes no significant difference to the arguments.

For CIE exam purposes, you won't be expected to know about pK_b. For the purposes of this page, all you need to remember is that the smaller the pK_b value, the stronger the base.

In an exam question, you are most likely to be expected to know that amines like phenylamine are much weaker bases than ammonia, and those like ethylamine are stronger. You will also be expected to be able to explain why.

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