Required Practical 10 - Preparation of pure organic solid/liquid Flashcards
Suggest role of sulfuric acid
Catalyst
Explain why it is important filter paper is wet during filtration of organic solid
- filtration proceeds faster
- prevents clogging of filter by solid
Suggest why a glass rod is used when transferring solutions
- prevent splashing
- control flow
Suggest why it is important not to remove funnel while water pump is still on
Water pump creates a vacuum which could damage filter paper if funnel is removed resulting in loss of filtered solid
Suggest why crude aspirin in added to ethanol AND cold water during purification
- ethanol added to dissolve everything
- cold water added to precipitate out aspirin ONLY
- ethanol alone causes aspirin to remain in solution
- cold water alone would precipitate out impurities
Suggest why prolonged heating of aspirin during purification should be avoided
To ensure aspirin does not decompose
Suggest why mixture is cooled in an ice bath during purification of aspirin
Aspirin more likely to precipitate out giving a better yield
Give reasons for loss in product during preparation and purification of solid
- reaction may not go to completion (reversible)
- side reactions may take reactants away
- not all substance is recrystallized
- lost in filtering/ transferring liquids
Suggest how the purity of an organic solid can be determined
- chromatography should only show one spot
- pure solid will melt at a precise temperature
- impure solid will melt over a WIDE range of temperatures + BEFORE the actual melting point
Suggest what is meant by glacial acid
Pure acid (not in solution)
Suggest why sodium carbonate is added in purification of organic liquid
Removes traces of carboxylic/sulphuric acid in distillate
Suggest why stop cock is opened in between inversions of separating funnel in preparation of organic liquid
- neutralisation of sodium carbonate produces CO2
- opening tap allows release of pressure which could blow stopper out of funnel
Suggest why remaining organic liquid from separating funnel is poured in a dry boiling tube containing anhydrous sodium sulfate
Dehydrating agent which removes traces of water
Suggest why a minimum volume of a hot solvent is used when purifying an organic solid
- obtain a saturated solution
- enable crystallisation upon cooling
Suggest safety precautions taken in preparation of pure organic solid
gloves - reactants are corrosive
water bath - avoids overheating
anti-bumping granules - slows down boiling
Suggest how to decide which solvent to use when purifying an organic solid
- dissolve when hot to remove insoluble impurities
- precipitate out when cold to remove soluble impurities
Suggest why filtration takes place through a pre-heated funnel in preparation of organic solid
So that the solution stays hot and does not recrystallize
Suggest organic solid is washed with a little cold solvent
To wash off any other soluble impurities
Suggest reason for drying organic solid
Remove any remaining solvent
Suggest why organic solid is packed densely into capillary tube when testing purity
You need enough solid to see it melt clearly
Suggest why it is important to ensure the apparatus heats up very slowly as the expected melting point of organic sold approaches
So you can observe the exact temperature at which it starts to melt
Suggest why concentrated sulfuric acid is added slowly and with cooling
- gives out a lot of heat
- avoid splashing if mixture get hot
Suggest advantages of reduced pressure (vacuum)filtration
- quick
- produces relatively dry product
Describe preparation and purification of organic liquid
- mix alcohol and carboxylic acid is round bottom flask
- add slowly with cooling a few drops of sulfuric acid
- shake well and reflux
- rearrange apparatus and distill
- transfer to separating funnel
- add sodium carbonate
- invert and open tap
- allow two layers to separate + run off lower layer
