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
how do impurities effect melting points + boiling points
Impurities lower the melting point (over a range) and increase the boiling point
how to determine melting point
need to ensure sample is dry + free flowing
take a glass capillary tube
hold one end into a bunsen burner
rotate until end is sealed
allow to cool
fill with crystals to about a 3mm depth (push the open end into the solid)
place into the melting point apparatus with a thermometer
once you see sample starts to melt - take temperature
repeat - but this time when the melting point is approached - set to low and raise the temperature slowly to get more accurate reading
how can some product be lost in purifying an organic solid
crystals lost when filtering / washing
some product may stay in solution after recrystallisation
other side reactions may occur
when an alcohol is dehyrdated 0 why do two layers form
aq + organic layers have different densities and are immiscible
why is the solution cooled in ice immediately after crystallisation
to decrease the solubility of the product so that it crystallises
lower temp increases size of crystals
explain why recrystallisation separates impurities
impurities are more soluble in the cold solvent - remain in solution
how to separate water soluble impurities
separating funnel
