Food Tests ( Class XII Chemistry practical experiments)

DATE:                                                                                                                                                 

                                                            EXPERIMENT NO. 

AIM :  To test the presence of reducing Carbohydrate in the given food sample.

MATERIAL  REQUIRED:  food sample,test tube, glass rod, water bath, Conc.

                                           H2SO4, Molisch reagent ( 1% alcoholic solution of α- 

                                         naphthol),Tollen’s reagent, Fehling solution & 

                                         Benedict’s reagent.

THEORY :  Carbohydrates are polyhydroxy aldehydes or ketones or compounds 

                  which give these on hydrolysis.

                 Carbohydrates which reduce Tollen’s & fehling’s reagent are called 

                 reducing sugars .

                All monosaccharides & disaccharides except Sucrose are reducing 

               sugars.

S.No.	EXPERIMENT	OBSERVATION	INFERENCE
1	Conc. H2SO4 test : Take a pinch of the sample in a test tube & add conc. H2SO4    ( heat if required).	Charring occurs with the smell of burnt sugar.	Carbohydrate is present.
2	MOLISCH’S TEST : To the aqueous solution of carbohydrate,add few drops of Molisch’s reagent & add conc. H2SO4    along the wall of the test tube.	A purple or violet colour ring is obtained at the junction of 2 layers.	Carbohydrate is present.
3	FEHLING’S TEST : To the aqueous solution of carbohydrate,add equal volumes of Fehling A ( Aq.CuSO4) & Fehling B ( Sodium potassium tartarate / Rochelle salt). Heat the contents in the water bath.	Red ppt. is obtained.	Carbohydrate is reducing in nature.
4	TOLLEN’S TEST: To the aqueous solution of carbohydrate,add Tollen’s reagent ( Ammonical Silver Nitrate). Heat the contents in the water bath.	Shining silver mirror is obtained on the inner sides of the test tube.	Carbohydrate is reducing in nature.
5	BENEDICT’S TEST : To the aqueous solution of carbohydrate,add Benedict’s reagent. Heat the contents in the water bath.	A red ppt. is obtained.	Carbohydrate is reducing in nature

RESULT :  The given food sample contains reducing carbohydrate.

PRECAUTIONS : 

• In Molisch’s test,conc. H2SO4 should be added along the wall of the tube without disturbing the solution.
• Water bath must be used carefully.

          

REACTIONS INVOLVED : Conc. H2SO4 Test :                     

FEHLING'S TEST :-----

TOLLEN'S TEST :-------

BENEDICT’S TEST :   

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DATE :              

                                                       EXPERIMENT NO. 

AIM :  To test the presence of Protein  in the given food sample.

MATERIAL  REQUIRED:  food sample,test tube, glass rod, water bath, NaOH, 

                                           CuSO4 solution & conc. HNO3.

THEORY :  Proteins are polymers of Amino acids which are made by Condensation 

                 polymerization reaction.

                    

                               

                    

                   

S.No	EXPERIMENT	OBSERVATION	INFERENCE
1	BIURET TEST : To 1-2 ml of suspension of food sample,add 1ml dilute solution of NaOH and few drops of copper sulphate solution dropwise.	Appearance of violet/purple colouration in the solution.	Protein is present.
2	XANTHOPROTEIC TEST : To 1-2 ml of suspension of food sample,add few drops of conc. HNO3 & heat.	Yellow precipitate is obtained.	Protein is present.

RESULT :  The given food sample contains Proteins in it.

PRECAUTIONS : 

• In Biuret test , CuSO4 solution should be added dropwise.

REACTIONS INVOLVED :

BIURET TEST :

                    

XANTHOPROTEIC TEST :

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DATE :                                                                                                                                                 

                                                EXPERIMENT NO.  

AIM :  To test the presence of Fats in the given food sample.

MATERIAL  REQUIRED:  food sample,test tube, glass rod, water bath, KHSO4, 

                                           Organic solvent like CCl4  & Filter paper.

.

THEORY :  Oil & Fats are triesters of Glycerol with higher fatty acids 

                    Triglycerides with higher proportion of unsaturated fatty acids are 

                    liquid at ordinary temp. & are called oils whereas triesters with  

                    higher proportion of  saturated fatty acids are solid & are called Fats.

S.No	EXPERIMENT	OBSERVATION	INFERENCE
1	SOLUBILITY TEST :  Add a few drops of the given food sample in 2-3 ml of water. Add a few drops of the given food sample in 2-3 ml of Organic solvent CCl4.	Does not dissolve dissolves	Oil/Fat present in the food sample.
2	SPOT TEST : Take a little quantity of the food sample on a piece of paper & press it between the folds of the paper.	A translucent spot appears which grows bigger on heating.	Oli/ Fat present.
3	ACROLEIN TEST : Take few drops of the sample & add Potassium bisulphate (KHSO4  ). Heat it strongly.	Pungent irritating odour of acrolein is produced.	Oli/ Fat present.

RESULT :  The given food sample contains Oil / Fat in it.

PRECAUTIONS : 

• In Acrolein test,Proper & careful heating of the sample should be done.

REACTIONS INVOLVED : ACROLEIN TEST :