4.6b Distillation, heating under reflux, vacuum filtration and recrystallisation

Question 1

What is distillation used for?

Answer 1

identification and purification of organic compounds

Question 2

What is one of the properties, determined by distillation, that can be used to confirm a compounds identity?

Answer 2

Boiling Point

Question 3

How can distillation be used to purify a compound?

Answer 3

by separating it from less volatile substances in the mixture

Question 4

What is the use of heating under reflux?

Answer 4

• allows heat energy to be applied to a chemical reaction mixture
• over an extended period of time
• without volatile substances escaping

Question 5

What is the process of heating under reflux?

Answer 5

• the reaction mixture is placed in a round-bottomed flask
• with antidumping granules and the flask is fitted with a condenser
• the flask is then heated using an appropriate source of heat

Question 6

Explain vacuum filtration

Answer 6

• carrying out as filtration under a reduced pressure
• provides a faster means of separating a precipitate from a filtrate
• a Büchner, Hirsch or sintered glass funnel can be used during vacuum filtration

Question 7

What is the method of recrystallisation to purify an impure solid?

Answer 7

• dissolving 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 8

how is the solvent for recrystallisation chosen?

Answer 8

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