PAG 7.3 - Oxidation reactions of carbonyl compounds

Give the method for Tollens’ test

1. Prepare Tollens’ reagent: in a clean test tube add 3cm³ of aqueous silver nitrate, AgNO_{3 (aq)}

2. Add aqeuous sodium hydroxide to the silver nitrate until a brown precipitate of silver oxide, Ag₂O, is formed

3. Add dilute ammonia solution until the brown precipitate just dissolves to form a clear colourless solution. This is Tollens’ reagent

4. Pour 2 cm depth of the unknown solution into a clean test tube and add an equal volume of freshly prepared Tollens’ reagent

5. Leave the test tube to stand in a beaker of warm water of 50C and observe whether any silver mirror is formed

Why is Tollens’ reagent prepared immediately before carrying out the test?

It has a short shelf life

How should you dispose of all the ammoniacal silver nitrate solution and why?

• Should be washed down the foul water drain with plenty of water

• It must not be stored as silver filaments will form, which have been known to explode

Give the method using acidified potassium dichromate (VI) solution

1. Put 1 cm³ of acidified potassium dichromate (VI) solution into a clean test tube and add 10 drops of the solution

2. Warm gently using a hot water bath

Give the results of the tests for distinguishing between aldehydes and ketones