Tag: pratical

How to prepare cyclohexane.

A while back in A level Chemistry we have been completing a practical on preparing a cyclohexane. Today’s blog post I will show the practical instructions with photos of our set ups and final product. This is to celebrate the ending of British Science Week 2020!

Part 1: preparation

Distillation apparatus
  1. Add 10cm3 of cyclohexane to a small round bottom or pear-shaped flask (CARE: don’t get it on your skin. Don’t inhale it. Keep away from naked flame.)
  2. Slowly add 4cm3 of concentrated phosphoric(v) acid and mix thoroughly (CARE: don’t get it on your skin. Mix slowly to prevent it getting too hot due to it being an exothermic reaction.)
  3. Add a few anti-bumping granules to the mixture, then set up the apparatus for reflux alongside an electric heater or sand bath (CARE: avoid splashing when adding granules.)
  4. Heat the mixture under reflux at 70oc for 15 minutes, adjust the heating and cooling rates to ensure that all condensation occurs in the lower half of the condenser (CARE: avoid water contact with electricity.)
  5. Stop heating and allow the glassware to cool for a few minutes (CARE: don’t touch the hot glass whilst it cools.)
  6. Rearrange the apparatus for distillation
  7. Raise the temperature and distil very slowly, collecting the distillate which comes over between 70oc and 90oc (CARE: don’t raise the temperature too fast. Don’t touch any apparatus which is hot.)

Part 2: purification

The pure cyclohexene we made
  1. Add an equal volume of saturated sodium chloride solution to the distillate in a separating funnel, shake gently and release any pressure build-up (CARE: avoid pressure build up and hence an explosion.)
  2. Allow the layers to separate and then discard the lower aqueous layer
  3. Wash the organic layer with an equal volume of water and discard the lower aqueous layer
  4. Run the remaining organic layer into a small conical flask
  5. Add a few lumps of anhydrous calcium chloride and swirl the mixture – if the liquid does not become clear, add more anhydrous calcium chloride and swirl again (CARE: avoid skin contact.)
  6. Finally decant the clear liquid into a weight container (CARE: avoid skin contact.)
  7. Reweigh the container and find the mass of cyclohexane that you have prepared (CARE: avoid skin contact.)
Using Bromine water to confirm that the product was an alkene as the bromine water should turn form orange to colourless when an alkene is present.

Part 3: organic functional group identification

  1. Test for the presence of carbon-carbon double bond in the product