purification Flashcards
3 steps to purify organic liquid
separate organic + aqueous layer using a separating funnel
add a drying agent
redistill at narrower temp range
what does each step in purifying liquid do
separating funnel - separates organic + aq layer
drying agents - removes excess water
redistill - removes organic impurities
what to do if theres acid impurities in liquid
add aq sodium carbonate
releases carbon dioxide
slowly open tap to release gas
how can you tell which is the organic layer + which is the aqueous layer in separating funnel
add distilled water and see which layer gets bigger
separating funnel method
ensure tap of funnel is closed
pour mixture into the funnel
place a stopper + invert
allow layers to separate
add distilled water to see which layers increase in volume - aq layer
empty into a conical flask
open tap regularly - release build up of pressure
examples of drying agents
drying agents method
add the organic liquid into a conical flask
add 1 spatula of drying agents + swirl
place a stopper to prevent product evaporating
decant the liquid from the solid
how can you tell if there is still excess water
if the solid has stuck together in a lump - there is still water
if the solid is dispersed as a fine powder // clear liquid - no more water
why may these liquids have organic impurities
boiling points relatively close together
the narrower the temp range - the purer the product
3 steps to purify an organic solid
filter under reduced pressure
recrystallisation
check purity
filter under reduced pressure method
connect one end of the pressure tubing to the vaccum / the filter pump / tap while attaching the other end to a Buchner flask
fit the Buchner funnel to the Buchner flask
switch on vaccum / tap
check for good suction
place a peice of filter paper inside buchner funnel
wet with the same solvent used in preparing the solid
pour the mixture into the funnel + rinse beaker to get all the solid
rinse the crystals in the funnel with more solvent + leave them to dry under suction for a few minutes so that the crystals start to dry
how do you check for suction in buchner funnel
place hand across the top of the funnel
recrystallisation method
Dissolve impure solid in minimum volume of hot
solvent
Cool solution first to room temperature and then to an ice bath
crystals form
collect crystals via filtration under reduced pressure
Scratch with glass rod
Wash with cold solvent/solvent and dry
how to choose the solvent for recrystallisation
depends on desired product and it’s solubility
you want the impurity to fully dissolve in cold solvent
how to check purity
determine the melting point + compare to a data base
