Esters

A series of free IGCSE Chemistry Activities and Experiments (Cambridge IGCSE Chemistry).

The following diagram shows the reactions of alcohol and carboxylic acids to make esters. Scroll down the page for examples and explanations.

Esters

• Describe the uses of esters.
  Esters are used as flavourings and fragrances.
• Describe the conditions needed to produce esters.
  The making of esters is also called esterification.
  Esters are made from carboxylic acids and alcohols.
  Ethanoic acid + ethanol ⇆ ethyl ethanoate + water
  with sulphuric acid as a catalyst
  CH₃COOH + C₂H₅OH ⇆ CH₃COOC₂H₅ + H₂O
• Describe the structure of the ester, ethyl ethanoate.
  The ester functional group is -coo-.

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Making esters from alcohols and acids
How to prepare an Ester from an alcohol and acid and separate by distillation?
In this activity, we will prepare a pure sample of ethyl ethanoate from ethanoic acid and ethanol.

1. Add 25 cm³ of ethanoic acid to the flask.
2. Add 25 cm³ of ethanol to the flask.
3. Add 10 drops of concentrated sulphuric acid as a catalyst and gently swirl the contents in the flask.
4. Warm the mixture in a warm bath for 15 minutes.
5. The boiling point of ethyl ethanoate is 77°C.
6. Set up the distillation apparatus.
7. Collect the ethyl ethanoate which will distill at 77° C.
8. Smell the product by gently wafting the odour towards your nose with your hand – do not put your nose near the top of the tube!

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Drawing and naming esters
How to name and draw the structures for esters (which form from alkanols and alkanoic acids in the process of esterification)?
alkanoic acid + alkanol ⇆ ester (akyl alkanoate) + water
ethanoic (acetic) acid + methanol → methyl ethanoate (acetate)
methyl methaoate → methanoic acid + methanol

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Questions

1. What is the general word equation for an esterification reaction?
2. What is the structural formula of ethyl ethanoate?
3. Because their structures are made up of two molecules that combine together, many esters have predictable isomers.

For example: methyl ethanoate will be an isomer of ethyl methanoate since the both have the same molecular formula: C₂H₆O₂
What would be an isomer of ethyl propanoate, for instance?

Answers

• Show Answers
  1. carboxylic acid + alcohol → ester + water
  2. CH₂COOCH₂CH₃
  3. propyl ethanoate

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