4. Esters

Question 1

State two properties of esters and their uses.

Answer 1

• Volatile with distinctive smells

• In perfumes and as food flavourings

Question 2

State the general formula for an esterification reaction and what is required.

Answer 2

Carboxylic Acid + Alcohol → Ester + Water

An acid catalyst

Question 3

Describe how to name an ester.

Using the example of pentanol and butanoic acid.

Answer 3

• 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

Question 4

State the functional group of an ester.

Answer 4

Question 5

Describe how to draw the displayed formula of an ester.

Answer 5

• Draw out the alcohol and carboxylic acid groups with their functional groups adjacent with eachother
• Remove a H from the alcohol and an OH from the carboxylic acid
• Combine the remaining parts of the alcohol and carboylic acid to form the ester
• Add the water as a product

Question 6

Describe how to prepare a sample of an ester such as ethyl ethanoate.

Practical

Answer 6

• Mix ethanoic acid, ethanol, and concentrated sulfuric acid.
• Heat gently using a water bath or electric heater (ethanol is flammable — no Bunsen burner!).
• As the ester forms, it is distilled off and collected by condensation in a separate beaker.
• Since esters are volatile (low boiling points), they evaporate first.
• Distillation removes the ester from the reaction mixture, preventing the reverse reaction (hydrolysis).

The distillate’s smell is tested — a sweet/fruity odour confirms the formation of an ester.