Experiment 22 Title: Reactions of aldehydes and ketones Aim: The purpose of this experiment is to compare some reactions of ethanal and propanone.
Introduction: 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 Requirements: Safety spectacles and gloves 6 test-tubes ethanal, CH3CHO ropanone, 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)) Procedure: 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.
. 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 drops of sodium hydroxide solution. 10. Drop-by-drop, add ammonia solution until the precipitate of silver oxide nearly dissolves (do not try to get rid of all the little black specks of silver oxide). 11.
Add 1 or 2 drops of ethanal, shake the tube gently and place in a beaker of warm water Note your observations and immediately rinse out the test-tube. 12. Repeat with propanone.
Part C Triiodomethane Reaction 13. Into an test-tube, place 5 drops of ethanal followed by 1 cm3 of iodine solution, cork and shake. 14. Drop-by-drop, add sodium hydroxide solution until the colour of iodine just disappears (about 2 cm3) and a straw-coloured solution remains. Note your observations. 15. Repeat with propanone.
Results Table: Test |Observations | | |Ethanal |Propanone | |A Condensation reaction with | | | |2,4-dinitrophenylhydrazine | | | |B Oxidation reactions: | | | |A acidified dichromate(VI) | | | |B Fehling’s solution | | | |C Tollens reagent | | | |C Triiodomethane reaction | | | Questions: 1. Which tests serve to distinguish between ethanal and propanone? 2. Which reagent could be used as a general test for a carbonyl compound?