Practical: making and testing the smell of some esters in the lab
4 marks · NormalGive the names of the starting alcohol and carboxylic acid used to prepare propyl ethanoate in the laboratory.
Briefly describe the steps you would take to make a small sample of propyl ethanoate, including any safety precautions.
State how you would detect the formation of propyl ethanoate after the reaction.
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) propan-1-ol and ethanoic acid
(b) Add 1 cm^3 of propan-1-ol and 1 cm^3 of ethanoic acid to a boiling tube, mix, then add a few drops of concentrated sulfuric acid. Place the tube in a beaker of hot water (about 80°C) for several minutes. Afterwards, cool and pour into a beaker half-filled with sodium carbonate solution. Wear goggles and avoid all skin contact. · must show correct steps, mention of safety (e.g., goggles, avoid contact)
(c) By gently wafting the ester’s odour or by noticing a layer of ester floating on the surface. · must show wafting smell, layer floating
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · Names both starting materials correctly: propan-1-ol and ethanoic acid.
M1 (b) · 1 mark · Describes main procedural steps (mix with acid, heat with hot water, add sulfuric acid, add sodium carbonate after cooling).
B2 (b) · 1 mark · Mentions at least one appropriate safety precaution, e.g., wearing goggles, avoiding skin contact, using fume cupboard.
B3 (c) · 1 mark · States the formation is detected by gently wafting the odour or by observing the ester layer on the liquid surface.
Worked solution
a) The starting alcohol is propan-1-ol and the carboxylic acid is ethanoic acid.
b) Mix 1 cm^3 of propan-1-ol and 1 cm^3 of ethanoic acid in a boiling tube. Add a few drops of concentrated sulfuric acid carefully. Place the tube in a beaker of hot water (around 80°C) for 5 minutes. Allow the mixture to cool, then pour into a beaker half-full of sodium carbonate solution. Wear safety goggles and do not touch acids with bare skin.
c) You could detect the ester by gently wafting the smell or by observing a layer of ester on the surface.