RP10- Aspirin

Question 1

The student purified the crude solid product, N−phenylethanamide, by
recrystallisation.
Outline the method that the student should use for this recrystallisation. (4)

Answer 1

1. dissolve in min vol of
2. hot water (/ solvent)
3. allow solution to cool + crystals form
4. filter off pure product under ↓ pressure

Question 2

Outline how you would carry out a simple laboratory process to show that the recrystallised product is a pure sample of N−phenylethanamide. (3)

Answer 2

1. measure mp
2. w/ mp apparatus
3. sharpmp that matches data source value

Question 3

A mixture of ethanol, ethanoic acid, and concentrated sulfuric acid, with anti-bumping granules, is heated under reflux for 10 minutes.
Give a reason why two layers form in the separating funnel.
Suggest why ethyl ethanoate forms the upper layer. (2)

Answer 3

1. ethyl ethanoate is immiscible w/ water
2. ethyl ethanoate is less dense than water

Question 4

The crude aspirin can be purified by recrystallisation using hot ethanol (boiling point = 78’C) as the solvent.
Describe two important precautions when heating the mixture of ethanol and crude aspirin. (2)

Answer 4

1. heat to below 78’C (so ethanol x boil away)
2. use water bath to heat x bunsen burner ∵ ethanol is flammable

⭐give practical step

Question 5

The pure aspirin is filtered under reduced pressure.
A small amount of cold ethanol is then poured through the Buchner funnel.
Explain the purpose of adding a small amount of cold ethanol. (1)

Answer 5

remove any soluble impurities

Question 6

A sample of the crude aspirin is kept to compare with the purified aspirin.
Describe one difference in appearance you would expect to see between these two solid samples. (1)

Answer 6

pure has larger crystals