filtration and recrystallisation

Question 1

what is vacuum filtration

Answer 1

this involves carrying out a filtration under reduced pressure and provides a faster means of separating a precipitate from a filtrate. a buchner, hirsch or sintered glass funnel can be used during vacuum filtration

Question 2

how does recrystallisation work

Answer 2

• dissolve an impure solid gently in a minimum volume of a hot solvent
• hot filtration of the resulting mixture to remove any insoluble impurities
• cooling the filtrate slowly to allow crystals of the pure compound to form, leaving soluble impurities dissolved in the solvent
• filtering, washing and drying the pure crystals

Question 3

how is the solvent for recrystallisation chosen

Answer 3

so that the compound being purified is completely soluble at high temperatures and only sparingly soluble at lower temperatures