Esters (Cambridge (CIE) A Level Chemistry): Exam Questions

Methanoic acid, HCO₂H, has a similar acid strength to propanoic acid.

Describe a chemical test to distinguish between these two acids. Name the acid which gives a positive result in this test and describe the observations that would be made.

The ester phenyl propanoate, C₂H₅CO₂C₆H₅, can be made from phenol and propanoic acid in a two step synthesis.

The first step produces an acyl chloride.

For this two step synthesis:

i) Draw the structure of the product of the first step.

[1]

ii) State the reagents and conditions needed for each step of the synthesis.

[2]

Explain why an acyl chloride should be formed first for the reaction in part (b).

Esters are responsible for various sweet, flowery and fruity smells. Some confectionery products use synthetic esters to achieve their aroma.

A student reacted acids and alcohols together to form ethyl methanoate (raspberry essence) and ethyl butanoate (pineapple essence).

Construct word and symbol equations to show the reactions that would produce these esters.

Octyl ethanoate can be manufactured or extracted from oranges and grapefruits. It is a flammable ester with a boiling point of 211 ^oC, a flash point of 86 ^oC and a density of 0.87 g/cm³.

A student reacted an acid and an alcohol in the presence of concentrated sulphuric acid to make an immiscible sample of octyl ethanoate. They added warm, aqueous sodium carbonate solution to remove any excess acid.

i) Explain why distillation would not work to safely obtain the octyl ethanoate.

[2]

ii) Describe the equipment that the student could use to safely obtain their octyl ethanoate and explain how this equipment would work.

[2]

Propan-2-ol reacts with ethanoic acid in the presence of a suitable catalyst

i) Construct an equation for the reaction, name the organic product and clearly show its structure

[3]

ii) Suggest a suitable homogeneous catalyst for the reaction.

[1]

The same organic product, from part (c), was synthesised using an alternative method.

Name an alternative reagent to react with the alcohol to form the organic product in part (c) and name the other product formed as part of the reaction.