Esters

7 marks · Hard

Esters are formed from an alcohol and a carboxylic acid in an esterification reaction. Ethanol and butanoic acid react together under suitable conditions.

(a)

Draw the full structural formula of the ester formed when ethanol reacts with butanoic acid.

[3 marks]

(b)

Name the ester formed in part (a).

[1 mark]

(c)

State one use of this ester in everyday life.

[1 mark]

(d)

Describe how esters like the one above are prepared in a laboratory. Include any catalyst and any condition needed.

[2 marks]

Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.

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(a) — · must show Full correct structure of ethyl butanoate: CH3CH2CH2COOCH2CH3, all bonds and atoms shown

(b) ethyl butanoate

(d) — · must show Heated with a few drops of concentrated sulfuric acid as catalyst, Heat is required for the reaction

Common mistakes: Swapping the alcohol and acid when naming the ester; Missing out water as a product; Missing the catalyst or heating step

Show mark scheme and worked solution

Marking points

M1 (a) · 1 mark · Bond between correct oxygen and carbon shown for ester linkage.

A1 (a) · 1 mark · All bonds and atoms shown correctly, no missing hydrogens/carbons.

A2 (a) · 1 mark · Structure of ethyl butanoate matches reaction described (not reversed).

B1 (b) · 1 mark · Correct name of ester: ethyl butanoate.

B2 (c) · 1 mark · A suitable use given, e.g. food flavouring, perfume.

M2 (d) · 1 mark · Sulfuric acid stated as catalyst.

A3 (d) · 1 mark · Condition of heating mentioned.

Worked solution

a. The full structural formula for ethyl butanoate is:

All carbon, hydrogen, and oxygen atoms must be shown. The ester linkage joins the carbonyl C of butanoic acid to the oxygen of ethanol after losing H2O.

b. Name: ethyl butanoate.

c. Use: Esters like ethyl butanoate are used as flavourings in food (or as perfumes/fragrances).

d. Description: To prepare an ester like ethyl butanoate in the lab, heat the alcohol and acid together with a few drops of concentrated sulfuric acid. The sulfuric acid acts as a catalyst.