Preparation and purification of organic compoundsEdexcel International A Level Chemistry: Flashcards

What these 14 flashcards ask

What is reflux used for?
When is steam distillation used?
Why does steam distillation work below 100 °C?
What is a separating funnel used for?
Why wash an organic product with sodium carbonate solution?
Why is the tap opened when shaking with sodium carbonate?
What are anhydrous magnesium sulfate and sodium sulfate used for?
How do you know a liquid is dry?
Why is the minimum volume of hot solvent used in recrystallisation?
Why is the solid washed with ice-cold solvent?
What does filtering under reduced pressure do?
How do impurities affect melting temperature?
What reagents make aspirin from salicylic acid?
Why is cold water added after making aspirin?

Exam questions on Preparation and purification of organic compounds

A student has prepared crude aspirin and purifies it by recrystallisation, using a hot mixture of ethanol and water as the solvent. Aspirin is much more soluble in the hot solvent than in the cold solvent.
After filtering the crystals, they are washed with a small volume of ice-cold solvent. Explain why the solvent is cold and why only a small volume is used.2 marks
A student prepares ethyl ethanoate by heating ethanol and ethanoic acid with a little concentrated sulfuric acid, then distils the mixture. The distillate contains ethyl ethanoate, ethanoic acid, ethanol and water. It is shaken with aqueous sodium carbonate in a separating funnel. The density of ethyl ethanoate is 0.90 g cm⁻³ and that of the aqueous layer is about 1.0 g cm⁻³.
The stopper is removed and the tap opened from time to time while the funnel is shaken. Explain why, including an equation.2 marks
A liquid Y is immiscible with water and boils at 190 °C, but it starts to decompose above about 150 °C. It is present in a reaction mixture together with a large amount of a black, non-volatile tar. A chemist uses steam distillation to separate Y from the tar.
Explain why steam distillation is a suitable method for separating Y from the tar.3 marks

Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).