Required practical 10a

Question 1

What is the aim

Answer 1

To make aspirin
Also learn how to do recrystallisation to purify product

Question 2

How is aspirin made

Answer 2

• 6g of salicylic acid to a weighing boat
• Record mass on scales, then tip the mass into 100cm3 conical flask and reweigh the boat
• Add 10cm3 ethanoic anhydride and swirl it, then add 5 drops of concentrated sulfuric acid
• Warm in a 60 degrees water bath
• Then allow the flask to cool and add contents to 75cm3 of cold water in a beaker
• Aspirin will start crystallising out
• Use buchner filtration under reduced pressure to filter it out

Question 3

How do we do recrystallisation of aspirin to make it more pure

Answer 3

• Add the smallest amount possible of hot ethanol so it dissolves both the aspirin and its impurities
• You want to use the minimum amount of solvent so that the crystals can reform easily
• Let cool so the crystals form
• Then pour over 40cm3 cold water
• Do buchner filtration under reduced pressure
• Blot the product with filter paper to remove excess water

Question 4

What effect do impurities have on melting point of a solid

Answer 4

They lower melting point

They also increase the range of melting point, so a pure substance has a sharp and sudden change from solid to liquid whereas impurities increase this range in melting.

Question 5

How does melting point of product indicate purity of it

Answer 5

The closer the melting point is to data book value, the more pure the substance is

Question 6

Why might you add some cold ethanol to it

Answer 6

To form bigger crystals

Question 7

What would you expect the difference in appearance be between pure aspirin and crude aspirin

Answer 7

Pure is whiter/lighter in colour

Pure aspirin has bigger crystals