Equation involved
C6H11OH C6H10 + H2O
H3PO4
C6H10 + H2O C6H10
CaCl2
Method
1. Place 0.1 mol of cyclohexanol in a flask and add 4cm3 of concentrated phosphoric acid by using the pipette while shaking the flask. It is because phosphoric acid is a dehydrating agent, so it will converts alcohols to cycloalkene.
Set up the distillation as below.
2.Heat the flask gently by use the burnser burner, it will distill very slowly, collecting the liquid which comes over between 70 and 90oC. it is because at a high temperature the liquid will turn to vapour gas more easier, but when the temperature too high, the pressure will be quite big, so that it will be quite dangerous and it might push the liquid straight to the other end.
Set up the separating funnel as below
3. Pour the distillate into a separating funnel and add an equal volume of a saturated solution of sodium chloride. Shake the funnel and allow the two layers to separate. Run off the lower aqueous layer and then run the top layer cyclohexene into a small conical flask. They are separated because of the density different.
Add two or three pieces of anhydrous calcium chloride and stopper the flask. It is to be able get rid of the water.
4. Weight the flask that we are going to collect the product by using electronic balance
5. Decant the alkene into a clean flask and redistill it, as what we have done in 1, the only different is distil it between 80-85oC.
6. Weight the product flask with the product together and minus the weight we get from 4, that is the product weight. Record it.
7. Separate the product to two equal volume to be use test on the product.. One of them add 1cm3 of bromine water. The other one add drop by drop to a small amount of potassium mangnate.
Results
Calculate the percentage yield
Theoretical yield: As cyclohexanol : cyclohexene is 1: 1, and their Ar are 100 and 82. so the yield come out should be 8.2g.
Percentage yield= the product we get/ theoretical yield=2.695/8.2* 100%= 32%
The reaction with bromine is positive,as the yellow color solution turns to colorless.
The reaction with mangnate is poitive, as the purple color solution change to green.
Conclusion.
The percentage yield we get are quite low. It is because there are lots lose in between we transfer the liquid from one flask to another. As well as this, during the distillation, when there is only a little liquid left in the flask, it is really difficult to distill it. As far as, we distilled twice, so I believe the loss from there is the most effective part.
Amy Chan
Chemistry practical
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