Wear goggles to prevent sodium getting in eyes and do not handle the sodium as it may react with skin – especially if wet. Do not test the gas with a lighted splint because sodium is flammable!
Bromine Test
Place 1cm³ of the organic compound in a test tube and add bromine water (which is an orange-brown colour) drop by drop until no further change. Shake the mixture. If the compound is an alkene – the bromine water will go colourless.
Safety:
Bromine is toxic and corrosive so wear gloves and goggles to prevent any getting into the eyes. It is also flammable so no naked flames.
Sodium hydrogencarbonate test
Place 2cm depth of the organic compound into a test tube and add a small amount of sodium hydrogencarbonate. If the compound reacts, bubbles will be seen (carbon dioxide gas).
Safety:
Wear goggles at all times to prevent any getting into eyes.
Ester test
- Hydrolyse compound by adding warm sodium hydroxide
- Add excess nitric acid and then carry out esterification:
Esterification 1:
- Place 1cm³ of glacial ethanoic acid into a test tube and add 2cm³ of unknown compound.
- Slowly add 2 to 3 drops of concentrated sulphuric acid.
- Warm the mixture in a water bath for 5 minutes.
- Allow to cool then pour the contents into a beaker containing 50cm³ of sodium carbonate solution. If a sweet – smell, then ester present.
Safety:
Concentrated sulphuric acid is corrosive, wear gloves and goggles when handling. Glacial ethanoic acid is corrosive and flammable so keep away from naked flames.
Acidified potassium dichromate test
- Place a few drops of acidified potassium dichromate solution in a boiling tube and add five drops of dilute sulphuric acid.
- Add a few drops of the organic compound and heat in a water bath for a few minutes.
- If orange to green then positive result.
Safety:
Wear goggles and gloves as sulphuric acid is corrosive and acidified potassium dichromate is an irritant.
Brady’s reagent – used to identify aldehydes and ketones.
- place 1cm depth of 2,4-DNPH in a boiling tube
- Add three drops of the organic compound.
- If orange precipitate forms this is a positive result.
2, 4-DNPH is toxic so wear gloves and use in a well ventilated area – preferably a fume cupboard.
Esterification 2:
- Place 1cm³ of unknown in a test tube with 2cm of ethanol.
- Add 2 to 3 drops of concentrated sulphuric acid and warm in a water bath for 5 minutes.
- Sweet smell is a positive result; this is the ester that has been formed.
Tollen’s Reagent (ammoniacal silver nitrate)
Tollen’s reagent acts as a mild oxidising agent so will not oxidise ketones.
- put 2cm depth of silver nitrate solution a boiling tube
- Add ammonia solution in drops and put boiling tube in a water bath at 60c. Stop adding ammonia solution when precipitate dissolves.
- Add three drops of organic compound in tube and if silver mirror on the inside of the tube, this is a positive result.
Safety:
No naked flames near ethanol as flammable. Silver nitrate is corrosive so wear gloves and goggles.
Reaction with iron (III) chloride²
- Add 20 drops of iron chloride solution to 5 drops of the compound. If phenol is present then this will give a purple colour.
Safety: Gloves and Goggles must be worn as phenol is corrosive.
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References:
1. A-Z Chemistry Handbook by Andrew Hunt. Pg 177 (hazards)
2. Chemistry in Action by Michael Freeman. Pg 748 (phenol)
