Practical Skills

Question 1

what is meant by heating under reflux?

Answer 1

boiling a mixture and condensing to return vapour to the flask
- to prevent evaporation of volatile compounds

Question 2

what are the steps of purification of an organic solid?

Answer 2

• dissolve crystals in minimum volume of hot water
• cool the solution to produce the crystals
• filter off crystals and wash with cold solvent
• … is more soluble in hot water than in cold water

Question 3

what are the steps of preparing organic liquids?

Answer 3

• ensure that the tap of the separating funnel is closed
• pour mixture of liquids into separating funnel, and place stopper in the top of the funnel and invert to mix the contents
• allow layers to settle
• place conical flask under separating funnel, remove the stopper and open the tap until the whole of the lower layer has left the funnel
• place second conical flask under searing funnel to collect other layer
• one conical flask = organic layer
• one conical flask = aqueous layer
• add drying alcohol

Question 4

how do you dry the organic product?

Answer 4

• add organic liquid to a conical flask
• using a spatula add some drying agent to liquid and gently swirl contents to mix together
• place stopper on flask to prevent product from evaporating
• if solid is a lump, water is still present so add more drying agent until a fine powder
• decant the liquid from the solid into another flask, if the liquid is dry it should be clear
• distil at 220 degrees celcius

Question 5

what are examples of drying agent?

Answer 5

• CaCl2 = anhydrous calcium chloride (drying hydrocarbons)
• MgSO4 = anhydrous magnesium sulfate (general drying)

Answer 6

3 and 4