How to Test for Ketones

Step-by-Step Guide

1. 1

   Step 1: Take a sample.

   You'll need a sample of whatever it is that you are wanting to test for ketones.
   
   If your sample is solid, you'll need to dissolve it.
   
   Do not use a solvent that contains a ketone group (e.g. acetone), or a solvent that will react with a ketone group.
   
   Water, hexane and ethanol are good solvents for this purpose. , The first will be tested to show the presence of C=O, and the second to show that it is a ketone., Be careful
   - 2,4-dinitrophenylhydrazine is an explosive! It will go off if handled dry.
   
   A red, orange or yellow precipitate indicates a carbonyl (C=O) group., Neither reagent should react with a ketone.
   
   If your solution contains any aldehydes, Tollen's reagent will produce a silver or grey precipitate (or a silver mirror on the side of the container), and Fehling's solution will produce a brick-red precipitate., 1st test positive and 2nd test negative = ketones. 1st test positive and 2nd test positive = aldehydes, possible mixture of aldehydes and ketones.
   
   If the 1st test is negative but you do the second test anyway, and get a positive result, then there are no ketones, but there is a reducing agent present.
   
   Try the first test again to make sure it wasn't a false negative.
2. 2

   Step 2: Divide your sample into two parts.

3. 3

   Step 3: Test the first sample with Brady's reagent (2

4. 4

   Step 4: 4-dinitrophenylhydrazine dissolved in methanol and sulphuric acid).

5. 5

   Step 5: If the first test is positive

6. 6

   Step 6: add Tollen's reagent or Fehling's reagent to the second sample.

7. 7

   Step 7: Interpret your results: 1st test negative = no ketones.

Detailed Guide

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