Practical 10

Question 1

After the solid benzoic acid has been filtered off, it can be purified.
Describe the method that the student should use to purify the benzoic acid.

Answer 1

Dissolve crude product in hot solvent/water
of minimum volume
Filter (hot to remove insoluble impurities)
Cool to recrystallise
Filter under reduced pressure / with Buchner funnel
wash (with cold solvent) and dry

Question 2

To test purity

Answer 2

Use a melting point apparatus, heat gently, a pure sample has a sharp melting point.

Question 3

Making aspirin equation

Answer 3

HOOCC6H4OH + (CH3CO)2 –> HOOCC6H4OCOCH3 + CH3COOH

Question 4

Cyclohexanol is converted into cyclohexene by dehydration using distillation with concentrated H2SO4.

Once the reaction is complete:

Answer 4

Place your crude liquid sample in a separating funnel.
Add an equal volume of saturated NaCl (aq) solution – ensures all water and polar compounds separate from the sample and dissolve in NaCl solution.
Shake and open the separating funnel to release pressure build up.
Let two layers separate out. – There will be an aqueous polar layer and a non-polar organic layer.
Use the tap at the bottom of the separating funnel to run off lower layer.
Add a drying agent to the sample eg anhydrous Na2SO4 to remove any remaining water.
Shake and allow to stand. The sample should go from cloudy to clear.