Practical: making and testing the smell of some esters in the lab
2 marks · HardDuring the purification step in ester preparation, the mixture is poured into sodium carbonate solution. Explain the purpose of this step and describe what you would observe.
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Also accept: to neutralise excess acid so ester smell can be detected more easily; an ester layer floats on top and effervescence is seen
Common mistakes: thinking sodium carbonate reacts with ester; failing to mention layer separation
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Marking points
B1 · 1 mark · Explains that sodium carbonate neutralises excess acid (allow: so the ester smell is not masked by acid).
B2 · 1 mark · Describes an observable effect: effervescence is seen and/or a separate ester layer floats on top.
Worked solution
The sodium carbonate solution neutralises the excess acid, which allows the ester smell to be detected more easily. You would observe bubbling (effervescence) as the acid reacts with the carbonate and a small layer of ester floating on top of the solution.