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PRACTICALS
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1 Combustion
The alcohols are alkanes with some oxygen within them, so they tend to burn with a clean, blue flame. Ethanol (contained in alcoholic drinks) is used in cookery to flambé food. The products of complete combustion are carbon dioxide and water.
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C2H5OH(l) + 3O2(g) ⇒ 2CO2(aq) + 3H2O(l) |
2 Reaction with sodium
It is important to be careful when disposing of the sodium metal as it can react violently with water. Watch the following video which shows a number of different alcohols reacting with sodium. What signs of reaction are there? Are the reactions similar for the different alcohols? What trend in reactivity is there and can you explain it? Try to write an equation for the reaction of sodium with ethanol. Check your answer in the theory link below.
Video - the reaction of sodium with alcohols
Theory - the reaction of sodium with alcohols
3 Reaction with phosphorus(V) chloride
This is a very lively reaction which produces hydrogen chloride gas so needs to be done in a fume cupboard. This gas can be tested for using ammonia gas. The reaction with phosphorus(V) chloride can be used to test for the presence of an OH group in an organic liquid. The reaction replaces the OH with a Cl making a chloroalkane:
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C2H5OH + PCl5 ⇒ C2H5Cl + POCl3 + HCl(g) |
Video - the reaction of ethanol with phosphorus(V) chloride
4 Oxidation with sodium dichromate(VI)
This reaction has a habit of bumping. This means a sudden production of vapour causes the boiling acid to be suddenly ejected from the boiling tube. This is why it should be only just brought to the boil. Always point the open end of the boiling tube away from people (including yourself!) and keep a careful eye out - people move!
Watch the video which shows the action of heating a mixture of orange sodium dichromate solution, dilute sulfuric acid and an alcohol. Alcohols in the range methanol to pentan-1-ol have been used. What signs of reaction can you see? Are the reactions similar for the different alcohols? Check your answer using the theory link below.
Video - oxidation of a range of alcohols
Observations and theory - oxidation of alcohols