IGCSEChemistryEdexcelRevision Notes4. Organic ChemistryEstersEsters

Esters (Edexcel IGCSE Chemistry): Revision Note

Exam code: 4CH1

Stewart Hird

Written by: Stewart Hird

Reviewed by: Lucy Kirkham

Updated on

Edexcel ChemistryEdexcel Chemistry (Modular): Unit 2

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Esters

Making esters

  • Alcohols and carboxylic acids react to make esters in esterification reactions

  • Esters are compounds with the functional group R-COO-R

    Diagram to show the ester functional group

  • Esters are sweet-smelling oily liquids used in food flavourings and perfumes

  • Ethanoic acid will react with ethanol in the presence of concentrated sulfuric acid (catalyst) to form the ester, ethyl ethanoate:

CH3COOH + C2H5OH → CH3COOC2H5 + H2O

Diagram showing the formation of ethyl ethanoate

Diagram to show the formation of ethyl ethanoate from ethanoic acid and ethanol

During this esterification reaction, a molecule of water is also produced

Naming Esters

  • An ester is made from an alcohol and carboxylic acid

  • The first part of the name indicates the length of the carbon chain in the alcohol, and it ends with the letters ‘- yl’

  • The second part of the name indicates the length of the carbon chain in the carboxylic acid, and it ends with the letters ‘- oate’

    • E.g. The ester formed from pentanol and butanoic acid is called pentyl butanoate

Diagram showing parts of an ester

Diagram showing the origin of each carbon chain in ester

  • Some examples of common esters:

Examples of Esters Table

Table showing the esters formed from different alcohols and carboxylic acids

Worked Example

Propanol reacts with ethanoic acid to form an ester

Name the ester formed and write its structural formula and displayed formulae.

Answer:

Step 1: Identify the two parts of the ester name

  • Propanol provides the first part of the ester name

    • propanol - propyl

  • Ethanoic acid provides the second part

    • ethanoic acid - ethanoate

  • Therefore, the ester is propyl ethanoate

Step 2: Write the part that comes from the carboxylic acid

  • Ethanoic acid has the structural formula CH3COOH

  • In the ester, the -OH of the carboxylic acid is used to form water

  • Therefore, the first part of the structural formula is CH3CO

Step 3: Write the part that comes from the alcohol

  • Propanol contains a chain of 3 carbon atoms CH3CH2CH2OH

  • The hydrogen atom bonded to the oxygen atom in the alcohol of is used to form water

  • Therefore, the second part of the structural formula is CH3CH2CH2O

Step 4: Join the two parts forming the ester link -COO-

  • CH3COOCH2CH2CH3

  • This is the structural formula of propyl ethanoate

Step 5: Turn the structural formula into a displayed formula

Displayed formula labelled “Propyl ethanoate”: CH3–COO–CH2–CH2–CH3, showing the ester link –COO– between the ethanoate and propyl groups.

Examiner Tips and Tricks

You must be able to write the structure and displayed formula for an ester, given the name or formula of the alcohol and carboxylic acid from which it is formed and vice versa.

Worked Example

The structural formula of an ester is:

CH3CH3COOCH3

Identify the alcohol and carboxylic acid used to make this ester.

Answer:

Step 1 : Identify the ester link

  • Esters contain the –COO– group

  • Use this group to separate the two parts of the ester:

CH3CH2COO | CH3

Step 2: Identify the part from the alcohol

  • The carbon chain attached to the oxygen is:

–CH3

  • This is the alcohol part of the ester

  • Alcohol: methanol

  • Structural formula: CH3OH

Step 3: Identify the part from the carboxylic acid

  • The part containing the C=O group contains a chain of 3 carbon atoms

  • This is the carboxylic acid part of the ester

  • Carboxylic acid: propanoic acid

  • Structural formula: CH3CH2COOH

Step 4: Write the ester name

  • The alcohol part is the first part of the ester name

    • Methanol turns into methyl

  • The carboxylic acid part is the second part of the ester name

    • Propanoic acid turns into propanoate

  • Therefore, the ester name is: methyl propanoate

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Stewart Hird

Author: Stewart Hird

Expertise: Chemistry Content Creator

Stewart has been an enthusiastic GCSE, IGCSE, A Level and IB teacher for more than 30 years in the UK as well as overseas, and has also been an examiner for IB and A Level. As a long-standing Head of Science, Stewart brings a wealth of experience to creating Topic Questions and revision materials for Save My Exams. Stewart specialises in Chemistry, but has also taught Physics and Environmental Systems and Societies.

Lucy Kirkham

Reviewer: Lucy Kirkham

Expertise: Content Creator

Lucy has been a passionate Maths teacher for over 12 years, teaching maths across the UK and abroad helping to engage, interest and develop confidence in the subject at all levels.Working as a Head of Department and then Director of Maths, Lucy has advised schools and academy trusts in both Scotland and the East Midlands, where her role was to support and coach teachers to improve Maths teaching for all.