Chemguide: Support for CIE A level Chemistry

Learning outcome 18: Carboxylic acids and derivatives

18.1: Carboxylic acids

Statements 18.1.2(a), 18.1.2(b) and 18.1.2(c): Reactions as acids

These statements are about reactions of carboxylic acids as acids. Read the individual statements as you go along.

You will find most of what you need on the page carboxylic acids as acids.

Some comments:

  • Don't worry about the relative strengths of these acids for the moment. (In other words, don't follow the link in the second green box.)

  • The syllabus describes the reactions with metals as a redox reaction. Hydrogen ions from the acid are being reduced to hydrogen gas by gaining electrons; metal ions are being oxidised to their positive ions by losing electrons.

  • The teacher support material for this statement specifies sodium as an example of reaction with a metal. You would get sodium ethanoate formed in a potentially dangerous reaction giving off hydrogen gas and a lot of heat. The equation for the sodium reaction is:

    It would be much more common to use the reaction between the acid and magnesium.

  • The use of sodium carbonate or sodium hydrogencarbonate to produce carbon dioxide gas is a useful test for the presence of an acid, including carboxylic acids.

  • The teacher support material mentions using a titration for the preparation of a salt like sodium ethanoate. You can titrate ethanoic acid (in the burette) against sodium hydroxide solution (in the flask) using phenolphthalein as the indicator. The indicator starts off bright pink, and you titrate to the point that the pink colour just disappears. There is more about choice of indicators in titrations in statement 7.2.10.

  • Ignore the section at the bottom of the page about the reactions with amines, for now. You won't meet reactions of amines until the second half of a course.

Statement 18.1.2(d): Producing esters

You should read the page about esterification of carboxylic acids.

Take your time over the introductory part of the page, and be sure that you understand how esters are named and drawn.

You will need some practical detail.

Statement 18.1.2(e): Reduction to give primary alcohols

Carboxylic acids are reduced to alcohols with LiAlH4. You will find everything you need on the page about the reduction of carboxylic acids.

The equation involving [H] is fine.

This reaction is also mentioned in statement 16.1.1(f) as a way of producing primary alcohols.

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© Jim Clark 2020