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A chemist synthesised benzoic acid in the laboratory and purified it by recrystallisation - Leaving Cert Chemistry - Question (b) - 2010
Question (b)
A chemist synthesised benzoic acid in the laboratory and purified it by recrystallisation. The melting point of the product was measured before and after recrystalli... show full transcript
Worked Solution & Example Answer:A chemist synthesised benzoic acid in the laboratory and purified it by recrystallisation - Leaving Cert Chemistry - Question (b) - 2010
Step 1
Give two ways the chemist could have concluded from the melting point measurements that the recrystallised product was purer than the material first prepared.
Answer
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Higher Melting Point: The chemist would observe that the melting point of the recrystallised product is higher than that of the crude product. This suggests a higher purity due to the presence of fewer impurities, which typically lower the melting point.
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Sharper Melting Range: The recrystallised product would also display a sharper melting point range (narrower range). Impurities usually broaden the melting range; hence a narrower range indicates a more pure substance.
Step 2
Name the instrumental technique that could have been used to confirm the identity of the product based on its absorption of a unique set of low energy electromagnetic radiations.
Answer
The instrumental technique used for this purpose is Infrared (IR) spectroscopy. This method analyzes the absorption spectrum of the sample, which provides information about molecular bonds and functional groups present in the compound.
Step 3