Practical: making and testing the smell of some esters in the lab
5 marks · HardA student is asked to prepare a sample of butyl propanoate, an ester, using only laboratory equipment and chemicals available at school.
Write the names of the alcohol and the carboxylic acid required to make butyl propanoate.
Describe, in order, the main steps the student should follow to prepare and purify butyl propanoate in the laboratory.
State how the student can safely test for the smell of the product once separated.
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.
Show answer
(a) butan-1-ol (alcohol), propanoic acid (carboxylic acid) · must show name of both correct reactants
(b) Add equal amounts of butan-1-ol and propanoic acid to a boiling tube, add a few drops of concentrated sulfuric acid, mix, heat in a beaker of hot water (~80°C) for several minutes, cool, then pour into sodium carbonate solution to separate the ester layer. · must show mix reactants in boiling tube, add concentrated sulfuric acid, heat in hot water bath, cool and add to sodium carbonate solution
(c) Use the wafting technique: gently waft the vapour towards your nose with your hand. · must show wafting technique described
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · Correctly names both butan-1-ol and propanoic acid as the reactants.
M1 (b) · 1 mark · Describes mixing the correct alcohol and acid in a boiling tube and adding a few drops of concentrated sulfuric acid.
M2 (b) · 1 mark · Describes heating the mixture in a hot water bath (not directly over a flame).
M3 (b) · 1 mark · Describes cooling and pouring the mixture into sodium carbonate solution to separate the ester.
B2 (c) · 1 mark · States that the smell is tested by wafting the vapour towards the nose.
Worked solution
a) The alcohol required is butan-1-ol and the carboxylic acid required is propanoic acid.
b) Procedure for laboratory preparation:
1. Add 1 cm³ of butan-1-ol and 1 cm³ of propanoic acid to a boiling tube.
2. Carefully add a few drops of concentrated sulfuric acid.
3. Mix thoroughly, then place the boiling tube in a beaker of hot water at around 80°C for about 5 minutes.
4. Allow the tube to cool. Pour the mixture into sodium carbonate solution to neutralise excess acid and release the ester as a separate layer.
c) Test for the smell by gently wafting the vapour towards your nose, not smelling directly above the tube.