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.

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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.

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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.

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Experiment O01 Chemical properties of alkenes

Name:

Seat No.:

Date:

Grade:

Results Table (Reaction of cyclohexenes)

Reaction / Observations
A / Combustion
Appearance of flame:
Sootiness: / 1.
2.
B / Action of bromine
(in1,1,1-trichloroethane) 1. In dark:
2. In light: / 1.
2.
C / Action of bromine water:
D / Action of acidified
potassium permanganate:
E / 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?

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