10 (3.9) Prep of organic solid/liquid

Question 1

Dissolve the impure compound in a minimum volume
of hot (near boiling) solvent?

Answer 1

An appropriate solvent is one which will dissolve both
compound and impurities when hot and one in which the
compound itself does not dissolve well when cold.
The minimum volume is used to obtain saturated
solution and to enable crystallisation on cooling

Question 2

Hot filter solution through (fluted) filter paper quickly.

Answer 2

This step will remove any insoluble impurities and heat
will prevent crystals reforming during filtration

Question 3

Cool the filtered solution by inserting beaker in ice

Answer 3

Crystals will reform but soluble impurities will remain in
solution form because they are present in small quantities
so solution is not saturated. Ice will increase the yield of
crystals

Question 4

Suction filtrate with a Buchner flask to separate out
crystals

Answer 4

The water pump connected to the Buchner flask reduces
the pressure and speeds up the filtration.

Question 5

Wash the crystals with distilled water

Answer 5

To remove soluble impurities

Question 6

Purifying an organic liquid

Answer 6

• Put the distillate of impure product into a separating funnel
wash product by adding either
sodium hydrogencarbonate solution, shaking and
releasing the pressure from CO, produced.
Saturated sodium chloride solution
•Allow the layers to separate in the funnel, and then run and
discard the aqueous layer.
•Run the organic layer into a clean, dry conical flask and add three
spatula loads of drying agent (e.g. anhydrous sodium sulphate,
calcium chloride) to dry the organic liquid. When dry the organic
liquid should appear clear.
• Carefully decant the liquid into the distillation flask
•Distill to collect pure product

Question 7

Sodium hydrogencarbonate?

Answer 7

Sodium hydrogencarbonate will neutralise
any remaining reactant acid

Question 8

Sodium chloride?

Answer 8

Sodium chloride will help separate the
organic layer from the aqueous layer

Question 9

Preparing + purifying cyclohexene

Answer 9

Pour about 20 cm° of cyclohexanol into a weighed 50 cm3 pear-shaped flask. Reweigh the flask and record
the mass of cyclohexanol.
b) Using a plastic graduated dropping pipette, carefully and with frequent shaking, add to the flask
approximately 8 cm3 of concentrated phosphoric acid.
c) Add a few anti-bumping granules to the flask and assemble the distillation apparatus, so that the contents
of the flask may be distilled. Heat the flask gently, distilling over any liquid which boils below 100 °C.
d) Pour the distillate into a separating funnel and add 50 cm} of saturated sodium chloride solution. Shake
the mixture and allow the two layers to separate.
e) run off the lower layer into a beaker and then transfer the upper layer, which contains the crude
cyclohexene, into a small conical flask.
f) Add a few lumps of anhydrous calcium chloride or anhydrous sodium sulfate(VI) or anhydrous magnesium
sulfate to the crude cyclohexene to remove water. Stopper the flask, shake the contents and allow this to
stand until the liquid becomes clear.
g) Decant the liquid into a clean, dry, weighed sample container.
h) Reweigh the container, calculate the mass of dry cyclohexene produced