organic purity/recrystallisation questions

obtaining a pure sample (not given density)

• shake and leave to settle in separating funnel

• separate layers by tapping off

• add anhydrous salt e.g CaCl2 or MgSO4 to organic layer

• redistill organic layer

• collect at [temp]

obtaining a pure sample (density and temp given)

• if an acid catalyst is used add neutralising agent e.g NaCO2

• specify where the organic layer is if its above 1gcm-3 then its at the bottom if its below 1gcm-3 e.g 0.74gcm-3 then its at the top

• separate the layers by tapping off

• add anhydrous salt e.g CaCl2 or MgSO4 to organic layer

• redistill and collect at [temp]

Recrystallisation impure to pure

• add minimum quantity of hot water

• cool solution and filter solid

• add cold water and leave to dry

checking purity

• determine melting point

• compare to known values

• pure samples have a sharp melting point