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Experiment 22

Reactions of aldehydes and ketones


The purpose of this experiment is to compare some reactions of ethanal and propanone.

We have chosen ethanal and propanone as relatively safe examples of aldehydes and ketones to illustrate their reactions in simple test-tube experiments. The reactions or properties to be investigated are as follows:

A. Condensation (addition-elimination)
B. Oxidation
C. Triiodomethane (iodoform) reaction


Safety spectacles and gloves
6 test-tubes
ethanal, CH3CHO
propanone, CH3COCH3
2,4-dinitrophenylhydrazine solution, C6H3(NO2) 2NHNH2
sodium hydroxide solution, 2 M NaOH
Bunsen burner, tripod, gauze and bench mat
Beaker, 250 cm3
Potassium dichromate(VI) solution, 0.1 M K2Cr2O7
Sulphuric acid, dilute, 1 M H2SO4
Fehling’s solutions 1 and 2
Silver nitrate solution, 0.05 M AgNO3
Ammonia solution, 2 M NH3
Iodine solution, 10% (in KI (aq))

Part A

Condensation reaction with 2,4-dinitrophenylhydrazine

1. Put 1-2 drops of ethanal in a test-tube and add about 2 cm3 of 2,4-dinitrophenylhydrazine solution. Note your observations. 2. Repeat for propanone.

Part B

Oxidation reactions

A.With acidified potassium dichromate (VI)
3. Into a test-tube, put 5 drops of ethanal, 2 drops of potassium dichromate (VI) solution and 10 drops of dilute sulphuric acid. 4. Shake the tube gently and warm in a beaker of hot water. Note your observations. 5. Repeat for propanone.

B.With Fehling’s solution
6. Into a test-tube, put about 1 cm3 of Fehling’s solution 1 and then add Fehling’s solution 2 dropwise until the precipitate just dissolves. 7. Add about 7 drops of ethanal. Shake the tube gently and place in a beaker of boiling water for 5-10 minuters – until no further colour change occurs. Note your observations. 8. Repeat for propanone.

C. With Tollens reagent

9. Put about 1 cm3 of 0.05 M AgNO3 into a very clean test-tube and add 3-4...
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