Experimental techniques

Why do you heat under reflux?
-When volatile liquids are being heated
– To prevent reactants/products from escaping whilst the reaction is in process
What are the steps when heating under reflux?
– Put the reactants in a pear-shaped flask
– Add anti-bumping granules
– Attach a condenser vertically
– Heat so the reaction mixture boils gently
Why are anti-bumping granules added when heating under reflux?
To prevent the reaction mixture from boiling and ‘bumping’ out of the flask
When heating under reflux, why is a condenser attached vertically above the reaction vessel?
To ensure any escaping vapours condense and return to the reaction flask and hence no product lost.
How do you purify an organic liquid after is has been synthesised?
Using a separating funnel
What techniques are used for purification?
Distillation
TLC
Recrystallisation
Vacuum filtration
Which techniques are used for analysis?
Determining melting point
Acid-base titration
Redox titration
Measuring a cell e.m.f.
Colorimetry
Measuring enthalpy change of combustion
What should the solvent for recrystallisation be?
One in which the desired substance is very soluble at high temperatures and insoluble (or nearly) at low temperatures
What are the steps involved in recrystallisation?
– Choose solvent
– Dissolve in minimum amount of hot solvent
– Filter to remove insoluble impurities
– Cool and allow crystals to form
– Collect the crystals by vacuum filtration
– Dry the crystals