Safety Precautions
In the tests to follow, wearing a lab coat, goggles (safety spectacles), and gloves are required. These experiments contain acid and other materials that can seriously harm health.
Reaction 1: Test for Cyclohexene
This is an alkene and as all alkenes, it may have a few uses, but they are reactive because of their carbon-carbon double bonds. When you mix bromine water with cyclohexene, it turns reddish brown bromine water colourless under dark conditions. Ethanol can be added to help aid the mixing. The equation for reaction of cyclohexene and bromine water is:
C6H10(l) + Br2 (l) → C6H10Br2 (l)
This is an addition reaction. The carbon-carbon double bond in the alkene ‘opens up’ and a bromine atom is ‘added’ on to both carbon atoms
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Put 2cm3 of cyclohexene into a test tube and place on a test tube rack.
- Wrap foil around the test tube.
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Add 2cm3 of 2% solution of bromine water into the test tube.
- Wait two minutes and then take the foil off.
- The liquid should decolourise.
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Safety: This liquid is highly flammable and the vapours mixtures are explosive. It should not be exposed to any open flame, sparks or any kind of smoking. It should also be kept in a closed system and any reactions carried out in a fume box. If exposed can cause redness to the eyes and skin, drowsiness, nausea and dry skin. Protective clothing, gloves and safety spectacles should be worn.
Reaction 2: Test for Butan-1-ol
Acidified potassium dichromate oxidise a primary alcohol like butan-1-ol. The reaction involves breaking the O-H bond of the alcohol. To test for Butan-1-ol using Acidified Potassium Dichromate(VI) is best as you will see it change colour from orange to green to show it’s a primary alcohol because an aldehyde has formed.
The equation for the reaction of Butan-1-ol and Acidified Potassium Dichromate (VI) is:
C4H9OH (l) + K2Cr2O7 → C4H8O + H2O
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In a boiling tube, mix 2cm3 of dilute sulphuric acid with 1cm3 of dilute potassium dichromate (VI) solution
- Add 5 drops of butan-1-ol and warm the mixture gently. Only allow to just boil.
- Cautiously smell the product.
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Safety: This liquid is flammable and should be kept away from any open sparks or flames. If above 29oC, explosive vapour mixtures may be formed. If used at this temperature use in a close system and make sure there is enough ventilation. If exposed can cause sore throat, headache, dizziness, redness to the eyes, abdominal pain and vomiting. Avoid all contact by using protective clothing, gloves and face shields. Do not eat or drink during the procedures.
Reaction 3: Test for Bromoethane
When testing for bromoethane it is best to use silver nitrate to identify the halide and you know it must be bromoethane because it’s your only chemical containing a halide. It should give a cream precipitate as AgBr if formed.
The equation for the reaction of bromoethane and silver nitrate is:
C2H5Br (aq) + AgNO3 (aq) → AgBr (s) + NO3 (g) + C2H5 (aq)
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Add 2cm3 of bromoethane to a test tube.
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Add 2cm3 of ethanoic silver nitrate to the test tube.
- Put a stopper on the test tube and give it a slight shake.
- The test tube should show a cream precipitate.
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Safety: This liquid is extremely flammable and should be kept away from open flames, sparks and any kind of smoking. It can also cause drowsiness, or redness of the eyes. To prevent this protective clothing, gloves and goggles should be worn. No eating or drinking should be done during the work.
Methlypropan-2-ol
In order to test this liquid it would be necessary to use Phosphorus Pentachloride PCl5 this will release hydrogen chloride gas which forms white misty acidic fumes in the air.
The equation for this reaction is:
C4H9OH + PCl5 → C4H9Cl + HCl + POCl3
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Add 2cm3 of methlypropan-2-ol to a test tube.
- In a fume cupboard, add a small amount of phosphorus pentachloride.
- Collect some of the fumes evolved in a “squeezed out” dropper and identify them by bubbling through some silver nitrate solution.
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OR identify the fumes with the stopper from an ammonia bottle.
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Safety: This liquid is colourless with a characteristic odour. The vapour mixes well with air and explosive mixtures are easily formed. The substance can be absorbed into the body by inhalation of its vapour and by ingestion. A harmful contamination of the air can be reached rather quickly on evaporation of this substance at 20oC. The vapour of this substance is irritating to the eyes and may cause effects on the central nervous system. Exposure at high levels could cause lowering of consciousness.
Reaction : Test for Ethanoic Acid
To test for Ethanoic Acid, you should add it to Anhydrous Sodium Hydrogen Carbonate. At the end of this reaction you should get a white crystal like solid, water and carbon dioxide.
CH3COOH + NaHCO3 → CH3CONa + CO2 + H2O
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Add 2cm3 of ethanoic acid to a test tube.
- Add a small amount of the anhydrous sodium hydrogen carbonate to the test tube.
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Safety: This liquid is flammable and should be kept away from any open sparks or flames. If above 39oC, explosive vapour mixtures may be formed. If used at this temperature use in a close system and make sure there is enough ventilation. If exposed can cause sore throat, headache, dizziness, blisters, redness to the eyes, abdominal pain and vomiting. Avoid all contact by using protective clothing, gloves and face shields. Do not eat or drink during the procedures.
Water
This is a very simple test that only involves a piece of blue chlorine cobalt paper pink.
- With the liquid in the test tube, get a piece of blue chlorine cobalt paper and place in the test tube.
- The paper should turn pink, indicating that the liquid is water.
