Ethene gas is prepared by dehydrating ethanol (drug found in alcoholic drinks). Ethene is a colourless gas with a sweet smell. It is a insoluble in water but can dissolve in organic solvents.
Main Chemicals required
- Ethanol – CH3CH2OH
- Aluminium oxide – a white powder in appearance – Al2O3
- Pour small amount of ethanol into a boiling tube.
- Push in a piece of glass wool to soaking up all the ethanol.
- Set up the apparatus with about 2g of aluminium oxide halfway along the boiling tube.
- Heat the aluminium oxide and occasionally heating the ethanol gently. The ethanol then changes to vapour, passes over the hot aluminium oxide and is dehydrated to produce ethene gas.
- Let the first few bubbles produced escape for a short time as this is mainly air. Than Collect 5 test tubes of the gas and put a stopper on each tube when it is filled.
- When the reaction has concluded, remove the delivery tube from the water first before turning off the bunsen burner. This is to prevent suck back.
- The gas burns with a luminous flame.
- The adding limewater to the test-tube turns limewater milky. This shows that carbon dioxide was formed when ethene burns in air.
Addition of Bromine Test
- Bromine water turns from yellow/red colour to colourless.
- The decolorisation of bromine is the standart test for unsaturation in a compound.
Addition of Acidified Potassium Permanganate (KMnO4) Test
- Purple colour to colourless.
- This is also used to test for presence of a C=C double bond (unsaturation).