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A LevelChemistryCIEExam Questions33. Carboxylic Acids & Derivatives (AL)33.2 Esters (AL)

Esters (AL) (CIE A Level Chemistry)

Exam Questions

28 mins3 questions
1a1 mark

Esters can be formed from carboxylic acids and acyl chlorides.

Write an equation for the formation of the ester formed from methanol and propanoic acid.

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1b2 marks

Propanoyl chloride can be prepared from propanoic acid. 

i)
Write an equation for the preparation of propanoyl chloride from propanoic acid and phosphorus(V) chloride. 

[1]

ii)
Give one observation of this reaction. 

[1]

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1c5 marks

Name and outline a mechanism for the reaction between methanol and propanoyl chloride to form methyl propanoate.

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1d2 marks

Describe two advantages of using propanoyl chloride over propanoic acid in the preparation of esters in industry.

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2a2 marks

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.

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2b3 marks

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,

  • draw the structure of the product of the first step
  • state the reagents and conditions needed for each step of the synthesis

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2c1 mark

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

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3a2 marks

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).

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

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3b4 marks

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)

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3c4 marks

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

i)
Write 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)

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3d2 marks

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.

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