Determining Aldehydic and Ketonic Group P2 Group 4
Determining Aldehydic and Ketonic Group P2 Group 4
Determining Aldehydic and Ketonic Group P2 Group 4
Organic Chemistry
Experiment 2: Determination of Aldehydic and Ketonic Groups
Introduction:
As far as oxidation is concerned, aldehydes are easily oxidized to carboxylic acids while
ketones require relatively stronger oxidising agents. Distinction can be made between
these two types of carbonyl compounds based on difference in their reactivity.
Materials:
Acetone
Formalin
Benzaldehyde
Acetaldehyde
Ethanol
Nitric Acid
2,4-Dinitrophenylhydrazine
Schiff’s reagent
Fehling’s solution A and B
Benedicts solution
2% AgNO3 solution
NaOH solution
Ammonium hydroxide solution (or dilute NH3)
250 mL beaker
Hot plate
8 Test tubes
8 dropper
Procedure:
A. Test given by both aldehydes and ketones
2,4-Dinitrophenylhydrazine test (2,4-DNP test)
1. Take 2-3 drops of the liquid compound in a test tube or in case of solid
compound, dissolve a few crystals of it in 2-3 mL alcohol.
2. Add a few drops of an alcoholic solution of 2,4-dinitrophenylhydrazine.
Appearance of yellow, orange or orange-red precipitate confirms the
presence of carbonyl group.
3. If precipitate does not appear at room temperature, warm the mixture in a
water bath for a few minutes and cool
Schiff’s test
1. Take 3-4 drops of the liquid compound or dissolve a few crystals of organic
compound in alcohol and add 2-3 drops of the Schiff’s reagent. Appearance
of pink colour indicates the presence of an aldehyde.
Fehling’s test
4.
Benedicts test
1. Add 5 drops of the liquid compound or the solution of the solid organic
compound in water or alcohol to 2 mL Benedict’s reagent.
2. Place the test tube in boiling water bath for 5 minutes. An orange red
precipitate indicates the presence of an aldehyde.
Tollen’s test
Note: You will be doing the same procedure for all the four organic samples to be
tested. Hence, four test tubes will be needed to prepare Tollen’s reagent
Note: During cleaning of the laboratory equipment, silver stains may not be easily
removed. You may take off these stains by adding concentrated nitric acid.
Objectives:
To learn how to use the scientific tools and chemicals and learn the
conventions of science.
To have a better grasp and understanding how chemicals work.
The procedures and reaction of different mixture and combination of
chemicals.
Results:
First, we put 1ml of silver nitrate in test tube and 3 drops of sodium hydroxide on the
silver nitrate solution then it became dirty or brown and then add drop wise of the
ammonium hydroxide solution, when we mixed and shake it, It dissolved the silver
nitrate. And lastly we add 2-3 drops of organic sample on the test tube containing the
tollen’s reagent, we put it to the boiling water bath and boiled it for about 2 minutes and
then after that as we observed the combined solution became a silver mirror.
Conclusions:
The organic sample that was added to the solution containing the Tollen's reagent (a
mixture of silver nitrate and sodium hydroxide) likely provided a source of carbon atoms
that were reduced to form the silver mirror. The reaction is likely taking place through a
series of steps, including the formation of silver nitrate solution by dissolving silver
nitrate in water. and adding of sodium hydroxide to the silver nitrate solution, which
reacts with the silver ions to form silver hydroxide and sodium nitrate and.also add
some drop of ammonium hydroxide to the solution, which reacts with the silver
hydroxide to form elemental silver and ammonium nitrate.and Lastly the addition of an
organic sample to the solution containing the Tollen's reagent, which provides a source
of carbon atoms that are reduced to form the silver mirror. While boiling the solution for
about 2 minutes, which helps to speed up the reaction and ensure that all of the
reactants are fully dissolved.
Photodocumentation:
https://theory.labster.com/tollens_procedure/