CH4 - Qualitative Test for Carbonyl Compounds
- Created by: beth-marie2511
- Created on: 07-04-16 20:34
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- Qualitative Tests For Carbonyl Compounds
- 2,4 - DNPH
- 1. Add a few drops of 2,4-DNPH to the solution under test.
- 2. A red/orange precipitate will form for a positive result.
- This indicates that the solution under test is a carbonyl compound.
- An aldehyde OR a ketone.
- This indicates that the solution under test is a carbonyl compound.
- 3. The precipitate formed will have a well defined melting point.
- The melting point can be measured and compared against known values to help with determining the name of the compound.
- Tollen's Reagent
- 1. Place 1cm3 of silver nitrate solution into a test tube.
- 2. Now add 1 drop of sodium hydroxide solution.
- A brown precipitate will form.
- 3. Add drops of ammonium hydroxide solution until the brown precipitate just dissolves.
- 4. Add a few drops of the solution under test to the freshly prepared Tollen's reagent.
- 5. Place this into a water bath.
- 6. A 'silver mirror' forming will indicate the presence of an aldehyde.
- No 'silver mirror' indicates that the carbonyl compound is a ketone.
- Fehling's / Benedict's Solution
- 1. Place 2cm3 of Fehling's / Benedict's solution into a test tube.
- 2. To this, add a few drops of the solution being tested.
- 3. Place the test tube into a water bath.
- 4. If a red precipitate forms this indicates the presence of an aldehyde.
- No reaction means that the carbonyl compound is a ketone.
- Iodine Solution & Sodium Hydroxide
- 1. Place 1cm3 of Iodine solution into a test tube.
- 2. Now, add 10 drops exactly of the solution being tested.
- 3. Add 1cm3 of Sodium Hydroxide solution.
- 4. A pale yellow precipitate will form which indicates:
- A) The presence of RCOCH3
- I.E. Methyl Ketone
- I.E. Ethanal
- OR B) The presence of a precursor to RCOCH3
- I.E. Ethanol or a secondary alcohol with the -OH group and Carbon 2.
- E.G. Propan-2-ol
- I.E. Ethanol or a secondary alcohol with the -OH group and Carbon 2.
- A) The presence of RCOCH3
- 2,4 - DNPH
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