This experiment needs to be carried out in a fume cupboard

• Weigh a 50ml round bottomed flask, pour 20ml of Cyclohexanol into the flask, and reweigh. Record the mass of Cyclohexanol

• Using a plastic graduated dropping pipette, very carefully and with frequent shaking, add to the flask 8mls of Concentrated Phosphoric Acid

• Add a few anti bumping granules to the flask and assemble the distillation equipment as below

• Heat the flask gently, distilling any liquid which boils below 100⁰C

• Pour the distillate into a separating funnel and add 50mls of saturated Sodium Chloride solution, shake the mixture and allow the 2 layers to separate

• Once separated run off the lower layer into a beaker

• Transfer the upper layer, which contains the crude cyclohexene into a small conical flask

• Transfer a few lumps of anhydrous Calcium Chloride to a weighing boat and add to the crude Cyclohexene to remove water

• Stopper the flask, shake the contents then allow this to stand until the liquid becomes clear

• Decant the liquid into a clean, dry weighed beaker

• Reweigh the filled beaker, calculate the mass of the dry Cyclohexene produced and determine the percentage yield of your product

• Test the distillate to confirm it contains an alkene

Test for an alkene

• Add approximately 1ml of your distillate into a clean, dry test tube

• Add equal amount of acidified Potassium Manganate (VII) solution, shake the contents of the test tube and record your observations

Calculating percentage yield

Percentage yield = mass obtained / expected mass x 100

Expected yield for dehydration of Cyclohexanol
Balanced equation

C₆H₁₁OH → C₆H₁₀ + H2O

Relative formula mass of both substances
Cyclohexanol    6 x 12 (C) = 72

                             1 x 12 (H) = 12

                             1 x 16 (O) = 16

                               = 100

Cyclohexene    6 x 12 (C) = 72

                            1 x 12 (H) = 12

                            1 x 16 (O) = 16

                               = 100

100g of Cyclohexanol should produce 82g of Cyclohexene

Reacting masses :

100/100=1g Cyclohexanol produces 82/100 g Cyclohexene

If we presume that we used 20g of Cyclohexanol

The expected yield should be –

82/100 x 20g = 16.4g

Testing for alkene

Acidified Potassium Manganate (VII) which is a purple solution will become colourless in the presence of an alkene

The Potassium Permanganate is a strong oxidising agent and will break the Carbon-Carbon double bond. As this reaction proceeds, the purple colour of the Potassium Permanganate will turn colourless.