Practical: making and testing the smell of some esters in the lab
4 marks · NormalThe table shows results from making esters by reacting different combinations of carboxylic acids and alcohols using the laboratory method described.
| Carboxylic acid | Alcohol | Ester layer observed? | Odour |
|---|---|---|---|
| Ethanoic acid | Ethanol | Yes | Sweet, fruity |
| Ethanoic acid | Propan-1-ol | Yes | Pear drop |
| Butanoic acid | Ethanol | Yes | Sweet, fruity |
| Propanoic acid | Propan-1-ol | No | - |
Suggest a reason why no ester layer was observed in the last experiment, compared to the others.
State one observation that would indicate an ester had formed in the other experiments.
In the experiment where ethanoic acid and propan-1-ol were used, what extra precaution should be taken when smelling the product? Explain your answer.
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(a) Not enough ester formed, or the ester’s solubility is too great for a visible layer; or conditions were not optimal.
(b) A sweet or fruity smell detected, or a layer of ester forming on the water surface.
(c) You should waft the odour gently towards your nose instead of smelling directly, because the reactants and products may be harmful or irritating, and the ester is volatile. · must show wafting, not smelling directly, reason: safety/harmful vapours
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Marking points
B1 (a) · 1 mark · Gives a plausible reason: low yield, high solubility, or suboptimal conditions.
B2 (b) · 1 mark · States either a layer on the liquid or a characteristic sweet smell as the observation.
M1 (c) · 1 mark · States to waft the odour, not smell directly.
A1 (c) · 1 mark · Explains this is for safety because reactants or vapours may be harmful.
Worked solution
a) No layer formed possibly because very little ester was produced, or the ester produced dissolves more in water.
b) Either a sweet, fruity smell or a layer of ester floating on the surface indicates ester formation.
c) The odour should be gently wafted towards the nose, not smelled directly, as the vapours may be harmful or irritating.