An experiment to prepare ethene gas from ethanol and examine its properties

Authors Avatar

An experiment to prepare ethene gas from ethanol and examine its properties:

Aim:

The purpose of this experiment was to prepare samples of ethene gas by dehydrating ethanol using aluminium oxide as a dehydrating agent and catalyst and then to perform various tests on the gas obtained to examine its properties.

Apparatus:

                 

Chemicals:

  • Ethanol
  • Aluminium oxide
  • Lime water
  • Glass wool
  • Bromine water
  • Acidified potassium permanganate solution (very dilute).
  • Water

Additional apparatus:

  • Boiling tube
  • Rubber stopper with hole
  • Delivery tube
  • Trough
  • Test- tube rack
  • 5 test tubes
  • 5 rubber stoppers for test tubes
  • Retort stand
  • Spatula
  • Bunsen burner
  • Glass rod
  • Splint
  • Matches

Diagram:

- Preparation of ethene gas:

Method:

(1) Preparation of ethene:

Pour some ethanol into the boiling tube to a 2-3 cm depth

Add some glass wool to soak up the ethanol, using a glass rod to push the wool down the tube.

Clamp the boiling tube in a horizontal position using a retort stand.

Put a small amount of aluminium oxide about half way along the boiling tube.

Complete the set up of the apparatus as shown in the diagram above.

Light the Bunsen burner, adjust it to a blue flame and heat the aluminium oxide. (Make sure the test tube is filled with water when you start to collect the gas produced.)

As the aluminium oxide gets hot the heat reaches the ethanol at the end of the tube. The ethanol then changes to vapour, passes over the hot aluminium oxide and is dehydrated to produce ethene gas.

Let the bubbles produced escape for a short time (these are mainly bubbles of displaced air). Collect 5 test tubes of the gas and put a stopper on each tube when it is filled.

When the test tubes have all been filled, loosen the retort stand and raise the apparatus so that the delivery tube no longer dips into the water. This avoids suck back of water as the tube begins to cool which could cause the boiling tube to crack. Turn off the Bunsen burner.  

(2) Testing the properties of ethene:

Combustion:

Remove the stopper of one of the tubes filled with ethene and apply a light to the mouth of the test tube using a lighted splint.

Allow the gas to burn and when it has stopped burning add a small amount of lime water to the test tube, stopper it and shake the tube a few times.

The limewater should turn milky white, showing that the gas burns in air to produce carbon dioxide.

This is the reaction that occurs:

C2H4 + 3O2 → 2CO2 + 2H2O

Addition of bromine:

Taking great care, add about 1/10th of the test tube of bromine water to one of the test tubes of ethene.

Join now!

Replace the stopper and shake the tube a few times.

The yellow/red colour should disappear to form a colourless solution.

In the presence of bromine, bromine is added across the carbon – carbon double bond in ethene to form a colourless alkane called 1,2 – dibromoethane and in the reaction above, when bromine in water is added to ethene, a colourless compound called 2- bromoethanol is produced . This means that adding bromine or bromine water is a common test for unsaturation.

Addition of acidified potassium permanganate:

Add about 1/10th of very dilute potassium permanganate solution to one of ...

This is a preview of the whole essay