required practical 10 Flashcards
why do we use reflux ?
allows an organic mixture to be heated without losing any reactants or products
why do we use anti bumping granules
to prevent vigorous or uneven boiling by making small bubbles instead of large bubbles
method to purify an organic liquid
put the distillate of impure product into a separating funnel
wash product by saturated sodium chloride solution which helps separate the organic layer from the aqueous layer
allow layers to separate in funnel and then run and discard aqueous layer
run the organic liquid into a clean dry conical flask and add 3 spatula loads of drying agent to dry the organic liquid
decant liquid into distillation flask
distil to collect pure product
what drying agent should you use ?
anhydrous calcium chloride
liquid will remain cloudy until all water drips have been removed
what 2 methods of washing are there
sodium hydrogen carbonate solution, shaking and releasing pressure from CO2 produced, it removes acidic impurities by neutralisation
saturated sodium chloride solution, helps separate organic layer from aqueous layer
what will the melting point be if sample is pure
sharp (same value as in data book)
what will melting point be if impurities are present
lowered and the sample will melt over a range of several degrees
how do we measure boiling point ?
method
distillation or set up a boiling tube in a heating oil bath
pressure should be noted
recrystallisation method
dissolve the impure compound in a minimum volume of hot solvent
hot filter solution through filter paper
cool the filtered solution by inserting beaker in ice
suction filtrate with a büchner flask to separate out crystals
wash the crystals with distilled water
dry the crystals between absorbent paper
what is an appropriate solvent
one which will dissolve both impurities when hot
and one which doesn’t dissolve itself when cold
why do we cool the filtrate
increases yield by ensuring all compound crystallises
where would we lose yield
crystals lost during washing or filtering
some product stays in solution after recrystallisation
side reactions occurring
