required practical 10: preparation of a pure organic solid and test its purity Flashcards
method of recrystallisation (aspirin)
dissolve the compound in a minimum volume of hot solvent - dissolves impurities + obtaining standard solution
hot filter solution is filtered to remove insoluble impurities
cool solution by placing in ice beaker - ice will increase yield of crystals
suction filtrate using buchner funner - reduced pressure will increase filtration
wash crystals with distilled water - removes soluble crystals
dry crystals with absorbent paper
why may yield not be accurate
crystals lost when filtering or washing
other side reaction
crystals not dried properly will have a greater mass
purification of aspirin
add ethanol to boiling tube
prepare beaker of hot water at 75 degrees
add crude aspirin to boiling tube and place in the beaker
swirl boiling tube until all the aspirin dissolves
poor contents into conical flask with water then allow to cool
filter solid using buchner funnel and allow to dry
measure final mass of the solid
how is purity of product measured
determining melting point of the sample and comparing with data book value
if product contains impurities melting point will decrease
how is melting point measured
fill capillary tube with sample and tie to thermometer and immerse in heated oil
method to prepare ethyl ethanoate
put anti bumping granules to pear shaped flask
add ethanol, glacial ethanoic acid and conc sulphuric acid to the flask whilst in a fume cupboard
set up beaker filled with water over a bunsen burner
clamp pear shaped flask in the beaker
heat under reflux
gently heat for 15 minutes
method to isolate ethyl ethanoate
add sodium carbonate whilst in pear shaped flask
transfer to separating funnel, stopper and invert, opening stop clock each time.
allow two separate layers to form, top layer is ethyl ethanoate as it is less dense than water
remove stopper, open stop clock and drain water
drain aqueous layer
transfer ethyl ethanoate to boiling tube and add magnesium sulphate (anhydrous) - agitate so any water is absorbed
decant ethyl ethanoate into a pair shaped flask
method of purification of ethyl ethanoate
add anti bumping granules to pair shaped flask
set up apparatus for distillation
place flask in 250cm3 beaker with water and clamp
heat water bath until ethyl ethanoate is boiling
record the temp at which vapour forms
distill ethyl ethanoate
weigh conical flask to work out final mass of ethyl ethanoate
why is sodium carbonate used when producing ethyl ethanoate
to react with any excess acid
why is stopper removed when producing ethyl ethanoate
to let out gas, which stops build up of carbon dioxide and build of pressure
why is anhydrous magnesium sulphate used to produce ethyl ethanoate
used as a drying agent
how is the purity of esters confirmed
work out boiling point of product and compare with data booklet
