Recrystallisation - WM

Question 1

What is recrystallisation

Answer 1

removal of small amount of impurities from a solid product

Question 2

Stages of recrystallisation

Answer 2

1. impure solid dissolved in the minimum amount of hot solvent. Any soluble impurities will dissolve as well
2. any insoluble impurities are removed by filtering while still hot
3. leave filtrate to cool. As it does the solid becomes less soluble in the solvent so starts to crystallise out. Any soluble impurities should stay in the solution as they are in much smaller quantities
4. collect crystals by vacuum filtration which will remove soluble impurities as they will be in the filtrate
5. wash the crystals with a small amount of cold solvent
6. dry the crystals

Question 3

How to know which solvent to use in recrystallisation

Answer 3

needs to be one that the desired product dissolve in well when hot but much less when cold so crystals form on cooling