Catalytic Cracking
About this practical...
You will know that we have too many long chain alkanes and can crack them to fulfil our need for shorter chains. Try your skill at completing the catalytic cracking process then see if you have managed to make an alkene by testing for it. Link it to the previous topic by explaining the role of the catalyst.
Method:
In this practical, it is crucial that you watch the teacher demonstration carefully first
1. Set up the apparatus exactly as shown by your teacher.
2. Your teacher will light your Bunsen once they have checked that the bung is in the test tube securely, the delivery pipe is under the water and that the area is safe to work in
3. Using a blue flame, heat the catalyst. (Once you start heating, remember that you cannot remove the heat until the delivery tube has been lifted from the water bath).
4. When hot, gently move the flame to warm the paraffin oil in the mineral wool then return to heating the catalyst. This should generate lots more bubbles through the water bath
5. Use the test tube that is full of water to collect bubbles until it has displaced all of the water, seal it with a bung for later
6. Lift the entire retort stand up so that the delivery tube is clear of the water bath, move the water bath and replace the retort stand back on the bench. Now you can stop heating and allow the apparatus to cool
7. Use bromine water to test to see if you have collected an alkene gas (your teacher may wish to complete this with the whole class together)
Safety & Managing Risks
Usual lab rules must be followed: loose hair tied back, goggles worn throughout the lesson, bags and stools tucked away and notify the teacher of any spills or breakages immediately. Take care when using the Bunsen. It is crucial that you keep heating the catalyst until the delivery tube is removed from the water. Check that your delivery tube has an opening in the rubber join for the gas to escape through. Leave the reaction tube to cool as it will be very hot. The bromine water will have hazard warnings. For more detailed information, please consult CLEAPSS.
Technician notes:
Pre-filled test tubes with ceramic wool at the base that has paraffin oil in it.
Broken ceramic crucible catalyst and spatulas
Test tubes (1 per set)
Delivery tubes with bungs (check slit present in rubber join)
Water baths
Bromine water with a pipette (staff use only)
This page was updated on: 8th January 2022