Experiment O01 Chemical properties of alkenes
Chemicals:
Cyclohexene (with teat pipette), (~5 cm3)
Bromine dissolved in 1,1,1-trichloroethane (with teat pipette), (10 drops)
Bromine water (with teat pipette), (5 drops)
Dilute sulphuric acid, 1M H2SO4 (1 cm3)
0.01 M KMnO4, (5-6 drops)
Concentrated sulphuric acid, (1 cm3)
Apparatus:
Hard glass watch glass,
Bunsen burner,
Long wood splints,
1 dry test-tube covered in aluminium foil,
5 dry test-tubes with corks to fit,
Test-tube rack,
Bench protection sheet,
Lamp with 100 watt bulb,
Safety spectacles,
Protective gloves.
Aim:
The purpose of this experiment is to test the reactivity of the alkenes by carrying out
some test-tube reactions on cyclohexene.
Introduction:
You will be using cyclohexene because it is one of the cheapest liquid alkenes. It has virtually the
same reactions as hexene and is similar to other alkenes.
Hazard warning:
Bromine is dangerously toxic and corrosive, especially in its liquid state. Solutions, such as
those used in this experiment, must also be treated with care. Therefore you MUST:
Do the experiment in a fume cupboard.
Keep the top on the bottle as much as possible.
Wear gloves and safety spectacles.
Cyclohexene is very flammable. Therefore you MUST:
Keep the top on the bottle as much as possible.
Keep the bottle away from flames.
Wear safety spectacles.
P.1
Experiment O01 Chemical properties of alkenes
Procedure:
A.
Combustion
1.
Place your watch glass on a bench protection sheet in the fume cupboard. Put on safety
spectacles and make sure the extractor in the fume cupboard is witched on.
2.
Using a teat pipette, place 3-4 drops of cyclohexene on the watch glass.
3.
Stopper and remove the bottle of cyclohexene to a safe place away from the watch glass and
any Bunsen flames.
4.
Pull down the front of the fume cupboard leaving a 30 cm opening.
5.
Light a long splint and use this to light the cyclohexene. Lower the front of the fume
cupboard to a 10 cm opening.
6.
Write down, in Results Table :
(a) the colour of the flame,
(b) whether you can see any soot produced.
B.
Reaction of bromine(dissolved in 1,1,1-trichloroethane)
1.
Place the test-tube covered with aluminium foil in a rack in the fume cupboard. Put an
uncovered tube alongside. Put on safety spectacles and gloves.
2.
Using a teat pipette, place approximately 2 cm3 of cyclohexene in each test-tube.
3.
Stopper the cyclohexene and remove it to a safe place away from flames.
4.
Pull down the front of the fume cupboard leaving a 30 cm opening.
5.
Using a teat pipette, place in each tube five drops of a solution of bromine in
1,1,1-trichloroethane.
6.
Stopper the bromine bottle.
7.
Shine the lamp on both test-tubes for about 3 minutes.
8.
Note the test and write down the result in your Results Table.
9.
Note the appearance of the contents of the clear test-tube.
10. Pour the contents of the test-tube covered with aluminium foil into a clean test-tube. Note
its appearance.
P.2
Experiment O01 Chemical properties of alkenes
C.
Reaction of bromine water
1.
Place a clean test-tube in a rack in the fume cupboard. Put on safety spectacles and gloves.
2.
Using a teat pipette, place approximately 1 cm3 of cyclohexene in the test-tube.
3.
Stopper the bottle of cyclohexene and remove it to a safe place away from the flame.
4.
Pull down the front of the fume cupboard leaving a 30 cm opening.
5.
Using a teat pipette, place 5 drops of bromine water in the test-tube.
6.
Stopper the bottle of bromine water.
7.
Cork and shake the test-tube.
8.
Note the appearance of the reaction mixture.
9.
Write down the result in your Results Table.
D.
Reaction of acidified potassium permanganate
1.
Place a test-tube in a rack in the fume cupboard.
2.
Using a teat pipette, place 3-4 drops of cyclohexene in the test-tube.
3.
Stopper and remove the bottle of cyclohexene to a safe place, away from flames.
4.
Pour into the test-tube approximately 1 cm3 of dilute sulphuric acid. Shake the mixture.
5.
Pour into the test-tube 5-6 drops of potassium permanganate solution and shake the mixture.
6.
Note the appearance of the reaction mixture.
E.
Reaction of concentrated sulphuric acid
1.
Place a test-tube in a rack in the fume cupboard.
2.
Pour into the test-tube approximately 1 cm3 of concentrated sulphuric acid.
3.
Pour into the test-tube approximately 1 cm3 of cyclohexene.
4.
Stopper and remove the bottle of cyclohexene to a safe place, away from flames.
5.
Note whether the substances mix or form two separate layers.
P.3
Experiment O01 Chemical properties of alkenes
Name:
Seat No.:
Date:
Grade:
Results Table
(Reaction of cyclohexenes)
Reaction
A
Observations
Combustion
1.
Appearance of flame:
2.
Sootiness:
B
Action of bromine
1.
(in1,1,1-trichloroethane)
1. In dark:
2.
2. In light:
C
D
E
Action of bromine water:
Action of acidified
potassium permanganate:
Action of conc. H2SO4:
Questions
1.
Would you expect ethene to be more or less reactive than ethane? Why?
2.
Why do you think alkenes produce a sootier flame than alkanes?
3.
Which test(s) could be used to distinguish between alkanes and alkenes?
P.4