PAG 05b: Synthesis of organic liquid- preparation of cyclohexene

Question 1

Write word and chemical equations for reaction that takes place when cyclohexanol is dehydrated

Answer 1

Cyclohexanol -> cyclohexene + water
C6H11OH -> C6H10 + H2O

Question 2

What is role of phosphoric acid in dehydration of alcohols?

Answer 2

Catalyst (speeds up rate of reaction)

Question 3

When an alcohol is dehydrated, why do 2 layers form in separating funnel?

Answer 3

The aqueous and organic layers have different densities and they are immiscible

Question 4

Why is it important to open stopper of separating funnel regularly?

Answer 4

Release the build up of pressure and reduce risk of apparatus breaking

Question 5

Cyclohexene can be produced from cyclohexanol. Why is sodium chloride added to mixture before it is separated with a seperating funnel?

Answer 5

To help remove most of the water from the solution

Question 6

Cyclohexene can be produced from cyclohexanol. Why is anhydrous calcium chloride added to the crude product?

Answer 6

To remove final traces of water- acts as a drying agent

Question 7

When cyclohexene is produced from cyclohexanol, is reflux or distillation apparatus used?

Answer 7

Reflux

Question 8

In the purification of the crude cyclohexene, is reflux or distillation apparatus used?

Answer 8

Distillation

Question 9

What is the purpose of anti-bumping granules?

Answer 9

• To prevent the formation of large gas bubbles that cause violent boiling
• During distillation, anti-bumping granules prevents the mixture boiling over into the condenser meaning impurities won’t contaminate the product.

Question 10

Describe the key features of the apparatus set-up for distillation

Answer 10

• Tilt the condenser down so any liquids flow into the beaker
• The water must enter at the bottom of the condenser and leave at the top for efficient cooling
• The collection flask should not be sealed to the condenser- it should not be airtight as the hot air in the system could cause the apparatus to crack
• Use a thermometer to identify when the desired product has evaporated from the reaction mixture

Question 11

How can percentage yield be calculated?

Answer 11

(Actual yield/ Maximum theoretical yield) x100

Question 12

Describe chemical test for an alkene

Answer 12

Add bromine water. If an alkene is present, there will be a colour change from orange to colourless

Question 13

Why might a water bath or electric heater be used instead of a bunsen burner to heat a reaction mixture?

Answer 13

If reactants are flammable, using a bunsen burner would be a safety risk

Question 14

What safety precautions should be taken when carrying out this practical?

Answer 14

• Cyclohexanol is harmful if inhaled or swallowed so keep lab well ventilated
• Concentrated phosphoric acid causes severe skin and eye burns so wear safety goggles and gloves when handling
• Anhydrous calcium chloride causes serious eye irritation so wear safety goggles
• Cyclohexene is fatal if swallowed so wash hands after use. It is also flammable so keep away from naked flames.
• Ensure the separating funnel stopper is firmly held in place and point the nozzle away from others when shaking