I have discussed all possible tests for distinguishing aldehydes and ketones. At first I have discussed the detection tests of carbonyl groups. Two important detection tests I have discussed, 1. 2,4-DNP test. 2. Sodium bisulfite test. After that I have discussed distinguish test for aldehydes..Here I have discussed 1. Fehling test 2. Benedict test. 3. Tollen's test or silver mirror test.4. Schiff test, 5. Chromic acid test. After that I have discussed two tests to distinguish aldehyde and ketone having alpha hydrogen..The tests are 1.nitropusside test 2. Janovsky test. Finally I have discussed about Iodoform test through which aldehyde and ketone having CH3C=O group can be detected.

1. Dr. Tanay Debnath
PhD
Chemistry
Mobile: 7044004256
tanay.iitk@gmail.com
Distinguish test for aldehydes and ketone

2. Aldehyde and ketone
Formaldehyde Acetaldehyde
BenzaldehydePyvaldehyde
Acetone
Benzophenone

3. Distinguish test only for aldehyde
1. Schiff’s Test:
2. Fehling’s Test:
3. Benedict's test:
4. Tollen’sTest:
5. Chromic acid test:
Distinguish test for aldehyde and ketone
1. Sodium bisulphite test:
2. 2,4-DNPH:

4. Distinguish test for Aldehyde and ketone having
CH3C=O group
1. Iodoform test:
Distinguish test for aldehyde and ketone
having alpha hydrogen
1. Nitroprusside test:
2. Janovsky Reaction:

5. NaHSO3
Acetaldehyde
NaHSO3
Proponone
Sodium bisulphite test for aldehyde and ketone
white crystalline solid
Observation
white crystalline solid
white crystalline solid

6. Yellow Orange
2,4-Dinitrophenylhydrazine
2,4-DNPH/Brady's reagent/Borche's reagent:
For aldehyde and ketone
1-(2,4-dinitrophenyl)-2-ethylidenehydrazine
+
Observation
Yellow Orange

7. Observation
Schiff’s Test for aldehyde
Pararosaniline/
Fuchsin
Schiff reagent
+
Ketone can’t do addition reaction as
it is hindered by bulky group
Schiff base:
Aldehyde/Ketone
+
Primary amine
Magenta colour
Magenta colour

8. Fehling’s Test for aldehyde
 Fehling A (CuSO4.5H2O)
 Fehling B (Alkaline solution of sodium potassium tartarate)
Observation
Deep blue to reddish brown
Benzaldehyde doesn’t respond in Fehling test.
 α-hydroxy ketone gives positive response in Fehling test
Na+
K+
CuSO4.5H2O
Deep blue complex
CH3CHO
Cu2O + CH3COOH
Reddish brown
Sodium potassium tartarate

9. Benedict’s Test for aldehyde
Observation
Deep blue to reddish brown
Sodium carbonate
Sodium citrate
CuSO4.5H2O
Cu(citrate)2
2-
Deep blue complex
CH3CHO
Cu2O + CH3COO-
Reddish brown
Used for detecting reducing sugar. It also gives positive test
for ketose like fructose as it has α-hydroxy ketone group.

10. Tollen’s Test for aldehyde
Observation
Silver mirror
[Ag(NH3)2]+
AgNO3
+
NaOH
Ag2O
NH3 +NaNO3
+
H2O
[Ag(NH3)2]++ Ag + CH3COO-
Silver mirror

11. Chromic acid test for aldehyde
Jones reagent
(CrO3 + H2SO4)
Observation
Orange to green/blue
RCHO + H2Cr2O7 = RCOOH + Cr2(SO4)3
Chromic acid
H2Cr2O7
Orange green/blue

12. Nitroprusside test for aldehyde and ketone
having alpha hydrogen
Observation
Red coloured complex
Na2 [Fe(CN)5NO].2H2O + NaOH
Red coloured complex
+ OH–→ – + H2O
[Fe(CN)5NO]2- + CH3COCH2
– → [Fe(CN)5NO.CH3COCH2]3-

13. Janovsky Reaction for aldehyde and ketone
having alpha hydrogen
m-dinitrobenzene + NaOH
NaOH
Observation
Purple coloured complex
Purple coloured complex

14. CHI3
Iodoform
Yellow ppt
I2 + NaOH
Iodoform test for Aldehyde and ketone having CH3C=O group
Observation
Yellow ppt
I2 + NaOH

15. Thank
You
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