Theory behind this practical:

In this practical, we are looking at a miniature scale version of catalytic cracking. In this immense industrial process, less useful, long chain alkanes are heated with a catalyst to crack them into shorter, more useful ones. When you collect your gas, you will hopefully collect a new type of hydrocarbon called an alkene which has a general formula of CnH2n.

Method:

Carefully set up the apparatus as shown in the picture, check that your teacher has seen the apparatus before you start heating the catalyst through the tube.

When you have filled the test tube for the second time and sealed it with a bung, stop heating and lift the whole apparatus from the water bath to prevent cold water being sucked back into the hot glass tube.

Take your sealed test tube to the teacher so that you can test for the presence of an alkene.

Leave all equipment to cool before dismantling and packing away.

Technician notes:

Check that the rubber tubes have a sufficient slit in them to prevent pressure build up when heating.

  • 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
  • Water baths
  • Bromine water with a pipette

Safety:

Usual lab rules must be adhered to:

  • Lose hair tied up
  • Goggles on throughout the lesson
  • Bags away and stools tucked under
  • Notify the teacher immediately if any spills or breakages occur
  • Take care not to inadvertently heat the clamps/stand.

For further/more detailed information, check all reagents and practices at CLEAPSS.