Chemguide: Support for CIE A level Chemistry

This statement is about the reactions of carboxylic acids to produce salts, esters and acyl chlorides.

Before you go on, you should find and read the statement in your copy of the syllabus.

Statement 10.6(b)(i): Producing salts

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 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(l) which you probably won't have done yet.

• You could ignore the section at the bottom of the page about the reactions with amines, for now. Amines are dealt with in section 10.7.

Statement 10.6(b)(ii): 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, either here or in statement 10.6(g). (I am not clear what the difference is between the present statement and that one, but as long as you know how esters are formed, including some practical detail, that should cover you.)

Statement 10.6(b)(iii): Producing acyl chlorides

You will find this on the page about converting carboxylic acids to acyl chlorides.

CIE's preferred method is using sulphur dichloride oxide (thionyl chloride) because the other products are gases, and so purification is easier. In case they come up in an exam question, you should be aware that either of the phosphorus chlorides can be used as well, but I wouldn't bother to spend much time learning the equations for these reactions.

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