Science - Chemistry - Organic Chemistry - 5 Carbonyl compounds
(P7172400)
5.2 Schiff's test and Fehling's test
Experiment by: Anouch
Printed: Feb 25, 2014 1:54:59 PM
interTESS (Version 13.12 B214, Export 2000)
Task
Task
How can aldehydes be distinguished from ketones?
Carry out the Schiff test and the test with Fehling's solution.
Use the space below for your own notes.
Logged in as a teacher you will find a button below for additional information.
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Additional Information
Learning objectives
• Aldehydes can be distinguished from ketones by their reaction with
fuchsin-sulphurous acid solution (Schiff's solution) and with Fehling's solution.
• The reactions of both solutions results from the oxidizability of aldehydes.
Ketones cannot be oxidized.
Notes on setup and procedure
Preparation:
Provide the oxidation products from the previous experiment (P7172300).
Remarks on the students experiments:
Ensure that the test tubes containing Fehling's solution are only carefully heated.
Boiling is delayed in these so that they tend to splash if heated to strongly.
Hazard and precautionary statements
Acetaldehyde (ethanal):
H224:
H319:
H335:
H351:
P210:
Extremely flammable liquid and vapour.
Causes serious eye irritation.
May cause respiratory irritation.
Suspected of causing cancer.
Keep away from heat/sparks/open flames/hot surfaces – No
smoking.
P223:
Keep away from any possible contact with water, because of violent
reaction and possible flash fire.
P281:
Use personal protective equipment as required.
P305+P351+P338:IF IN EYES: Rinse cautiously with water for several minutes. Remove
contact lenses if present and easy to do – continue rinsing.
P308+P313:
IF exposed or concerned: Get medical advice/attention
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Acetone (propanon):
H225:
H319:
H336:
P210:
Highly flammable liquid and vapour.
Causes serious eye irritation.
May cause drowsiness or dizziness.
Keep away from heat/sparks/open flames/hot surfaces – No
smoking.
P233:
Keep container tightly closed.
P305+P351+P338:IF IN EYES: Rinse cautiously with water for several minutes. Remove
contact lenses if present and easy to do – continue rinsing.
Fehling's solution I:
H411:Toxic to aquatic life with long lasting effects.
P273: Avoid release to the environment.
Fehling's solution II:
H314:
Causes severe skin burns and eye damage.
P280:
Wear protective gloves/protective clothing/eye protection/face
protection.
P305+P351+P338:IF IN EYES: Rinse cautiously with water for several minutes. Remove
contact lenses if present and easy to do – continue rinsing.
P309+311:
IF exposed or you feel unwell: Call a POISON CENTER or
doctor/physician.
Hazards
• Acetaldehyde and acetone are highly inflammable. Extinguish all open flames
when handling them! Wear protective glasses!
• Remove all stock bottles before igniting the Bunsen burner. Position the Bunsen
burner sufficiently well away from the test tubes!
• Acetaldehyde is harmful to health. Do not inhale it!
• Carry out the experiment in the fume hood!
Notes
These and other reactions which differentiate aldehydes from ketones (silver mirror)
result from the oxidizability of the aldehydes, due to the presence of an additional
hydrogen on the carbon atom.
Remarks on the method
Knowledge of the oxidizing potential of the Fehling's solution is necessary to
answer question 3, so that this topic has to be discussed prior if the students are not
familiar with it.
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Waste disposal
• Filter off copper oxide from the Fehling's solution and put it in the heavy metals
waste
• Put the remaining solutions into the container for combustible organic waste.
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Material
Material
Material from "TESS advanced Chemistry Set Organic Chemistry, CH-4 " (Order
No. 15304-88)
Position No. Material
Order No. Quantity
1
Test tube, 180x18 mm
37658-10
(8)
2
Pipette with rubber bulb
64701-00
4
3
Test tube rack for 12 tubes, holes d = 22 mm, wood
37686-10
1
4
Test tube holder, up to d = 22 mm
38823-00
1
5
Test tube brush w. wool tip, d = 25 mm
38762-00
1
6
Protecting glasses, clear glass
39316-00
1
7
Lab. pencil, waterproof
38711-00
1
Chemicals, Additional Material
Position
No.
Material
Order No. Quantity
Bunsen burner /DIN/, nat.g., w. cock
32168-05
1
Safety gas tubing, DVGW, sold per metre
39281-10
1
Acetaldehyde, 98-100%, 250 ml
30001-25
Acetone, extra pure, 1 l
30004-70
Fehling's solution I, 250 ml
30079-25
Fehling's solution II, 250 ml
30080-25
Schiff's reagent, 250 ml
31827-25
Oxidation product of 1-propanol from the experiment
"Oxidation of alcohols" (P7172300)
Oxidation product of 2-propanol from the experiment
"Oxidation of alcohols" (P7172300)
Material required for the experiment
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Setup
Setup
Hazards
• Acetaldehyde and acetone are highly inflammable. Extinguish all open flames when
handling them! Wear protective glasses!
• Remove all stock bottles before igniting the Bunsen burner. Position the Bunsen burner
sufficiently well away from the test tubes!
• Acetaldehyde is harmful to health. Do not inhale it!
• Carry out the experiment in the fume hood!
Setup
Number the test tubes from 1 to 8.
Fill Schiff's reagent into test tubes 1 to 4 up to a height of about 2 cm. Fill Fehling's solution
I into test tubes 5 to 8 up to a height of about 1 cm, add about the same amount of Fehling's
solution II until a deep blue solution is formed (Fig. 1).
Fig. 1
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Action
Action
Procedure
Pipette one drop of acetaldehyde into test tube 1 and two drops of acetaldehyde into test tube
5.
Change the pipette and put one drop of acetone into test tube 2 and two drops of acetone
into test tube 6 (Fig. 2).
Fig. 2
Use the third pipette to put two drops of the solution containing the oxidation product of
1-propanol (will be supplied by the teacher) into test tube 3 and five drops of it in test tube
7.
Use the last pipette to put two drops of the solution containing the oxidation product of
2-propanol (will be supplied by the teacher) into test tube 4 and five drops of it in test tube
8.
Briefly heat the test tubes 5 to 8 in the flame of the Bunsen burner, one after the other. Shake
them a little while doing this, but without causing the liquids to splash out.
Do not heat to boiling!
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Fig. 3
Waste disposal
Leave the test tubes in the test tube rack for disposal.
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Results
Results
Note your observations and summarize them in the table.
Table 1
Schiff's test
Fehling's test
acetaldehyde
(ethanal)
acetone
(propanone)
oxidation product
of 1-propanol
oxidation product
of 2-propanol
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The fuchsin-sulphurous acid solution (Schiff's solution) turns violet on the addition
of acetaldehyde and the oxidation product of 1-propanol. Acetone and the oxidation
product from 2-propanol do not cause this reaction. On adding Fehling's solution II
to Fehling's solution I, a dark-blue solution is formed. This reacts with acetaldehyde
and the oxidation product from 1-propanol to form a yellowish-red precipitate.
Acetone and the oxidation product from 2-propanol do not perform this reaction.
Schiffs test
acetaldehyde
positive
(ethanal)
(violet colour)
Fehling's test
positive
(yellowish-red
precipitate)
acetone
(propanone)
negative
oxidation product
positive
of 1-propanol
(violet colour)
negative
positive
(yellowish-red
precipitate)
oxidation product
of 2-propanol
negative
negative
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Evaluation
Evaluation
Question 1:
Draw conclusions from your observations.
Aldehydes react with Schiff's solution and Fehling's solution, forming characteristically
coloured substances. An aldehyde must have been formed by the oxidation of
1-propanol, on the oxidation of 2-propanol a ketone was formed.
Question 2:
Formulate a mnemonic sentence which allows to differentiate between aldehydes and ketones.
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Aldehydes react with Schiff's solution to give a violet colour and with Fehling's solution
to give a yellowish-red precipitate. Ketones do not react.
Question 3:
Which property of the aldehydes is the basis for discriminating them from ketones?
2+
1+
The Cu ions in Fehling's solution are reduced to Cu
oxidizable, ketones are not.
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ions. Aldehydes are therefore