purification by recrystallisation: steps + explainations Flashcards
1
Q
give the 6 steps to purification by recrystallisation
A
- dissolve crude product in hot solvent/water
- of minimum volume
- filter
- cool to recrystalise
- filter under reduced pressure/ with Buchner apparatus
- wash (with ice cold solvent) and dry
2
Q
why do you do this?
- dissolve crude product in hot solvent/water
A
to dissolve as much as possible
3
Q
why do you do this?
- of minimum volume
A
to make sure hot solution is saturated/crystals form on cooling
4
Q
why do you do this?
filter
A
to remove any soluble impurities
5
Q
why do you do this?
cool to recrystalise
A
yield is lower if warm/solubility higher if warm
6
Q
why do you do this?
filter under reduced pressure/with Buchner appartus
A
crystal compressed in Buchner funnel to allow for better drying as air passes through the sample
7
Q
why do you do this?
wash with ice cold solvent and dry
A
to wash away soluble impurities
