Qualitative tests for Urea in given sample [CCF-SEMV-DSCC-11-P]

 

[Test Solution Required: 2% Urea solution in distilled water.]

Experiment	Observation	Inference
Hypobromite Test: A few drops of freshly prepared alkaline sodium hypobromite is added to about 3ml of sample solution.	A marked effervescence occur.	Urea is present .
[Chemical reason:  The effervescence is due to  evolution of nitrogen which occurs during the reaction. ➡️NH2CONH2 + 3NaOBr         N2 ⬆️  + CO2 ⬆️ + 3NaBr + 2H2O Sodium Hypobromite (NaOBr) decomposes urea, liberating N2 & CO2,the last being absorbed by alkali. [CO (NH2)2 +3 NaOBr    ➡️  3NaBr + N2  ⬆️ + CO2+2H2O CO2 +2NaOH  ➡️   Na2CO2 +H2O] The complete equation is  (NH2)2CO + 3NaOBr + 2NaOH  ➡️  N2  ⬆️   + Na2CO3 + 3NaBr + 3H2O] [Reagent Preparation Sodium hypobromite is unstable and is usually prepared fresh (in situ) by reacting bromine with cold sodium hydroxide:Br2 + 2NaOH ➡️    NaBr + NaOBr + H2O]
Nitrate Test: A drop of Concentrated HNO3 to a drop of a concentrated solution of Urea.	Octahedral lozenge shaped crystals are formed. [Urea nitrate ]	Urea is present.
Biuret Test:[Confirmatory Test] Evaporate 5ml of sample solution over a low flame to get the crystal form.After cooling dissolve the residue in dil.NaOH & add 1or 2 drops of 1%CuSO4 Solution.	Pink colour [Bi-uret] is obtained in the solution.	Urea is Present.
Chemical reason:  Heat decomposes urea into ammonia & cyanic acid. At high temperature the cyanic acid is partially polymerized to cyanuric acid & partially combines with unchanged urea to biuret form. CO(NH2)2  ➡️   HNCO [Cyanic acid] + NH3 [Ammonia]   ➡️HN.CO + CO(NH2)2         H2NCO.NH.CONH2  [Biuret]

Qualitative Test for Uric Acid: https://biomassfootprints.blogspot.com/2025/12/qualitative-tests-for-uric-acid-in.html

Qualitative Test for Ammonia: https://biomassfootprints.blogspot.com/2025/12/qualitaive-test-for-ammonia.html