Esters
6 marks · NormalA student wants to prepare methyl propanoate in the laboratory using appropriate organic starting materials.
Identify the alcohol and the carboxylic acid required to make methyl propanoate.
Draw the structural formula for methyl propanoate.
Describe briefly, in two steps, how a small sample of methyl propanoate can be prepared and the smell detected during a school practical.
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) methanol and propanoic acid · must show Methanol, Propanoic acid
(b) CH3CH2COOCH3 · must show propanoate part (CH3CH2COO), methyl group (CH3) joined via COO
(c) Step 1: Mix methanol and propanoic acid with a few drops of concentrated sulfuric acid in a boiling tube, and heat gently in a water bath. Step 2: After reaction, pour the mixture into sodium carbonate solution and note the ester layer and smell. · must show heating with sulfuric acid, pour into sodium carbonate, observation of ester layer/smell
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Marking points
A1 (a) · 1 mark · Names methanol as the correct alcohol.
A2 (a) · 1 mark · Names propanoic acid as correct acid.
M1 (b) · 1 mark · Correct structure of methyl propanoate using either condensed or displayed formula.
A3 (b) · 1 mark · All bonds and atoms shown correctly. (follow-through)
M2 (c) · 1 mark · Describes heating mixture of acid and alcohol with concentrated sulfuric acid.
A4 (c) · 1 mark · States pouring into sodium carbonate and smelling/detecting ester layer.
Worked solution
a) The alcohol required is methanol. The carboxylic acid required is propanoic acid.
b) The structural formula for methyl propanoate is:
c) Step 1: Place methanol and propanoic acid in a boiling tube, add a few drops of concentrated sulfuric acid, and heat in a hot water bath. Step 2: Cool, then pour contents into sodium carbonate solution; observe a layer of ester floating, and gently waft the smell.