APPARATUS - Test tubes, burner, litmus paper, beaker, tripod stand, conical flasks, burette, pipette.
CHEMICALS REQUIRED –
1. Fehling’s solution A
2. Fehling’s solution B
3. Tollen’s reagent (Ammoniacal AgNO3)
4. Benedict’s solution
5. Iodine solution
6. Chloroform (CHCl3)
7. Concentrated nitric acid (HNO3)
8. Concentrated Sulphuric Acid (H2SO4)
9. Ethyl Alcohol (C2H5OH)
10. Alkaline copper sulphate (CuSO4 + NaOH)
11. Aqueous sodium bicarbonate (NaHCO3)
A. Fruit juices that were analysed :-
(i) Apple
(ii) Coconut
B. Vegetable juices that were analysed :-
(i) Tomato
The various experiments and tests performed under the project gave qualitative analysis to find the presence of various organic compounds such as carbohydrates, proteins, fats & oils, carboxylic & hydroxyl & aldehydic groups in the juices of fruits and vegetables.
THEORY :
1. CARBOHYDRATES
Carbohydrates are chemical compounds of carbon, hydrogen, oxygen with general formula Cn(H2O)n. They have two or more hydroxyl groups and one aldehydic/ketonic group.
Identification Tests
A. Fehling’s solution Test (given only by reducing carbohydrates)
Fehling’s solution is an alkaline solution of copper sulphate containing sodium potassium tartrate (Rochelle salt) as the complexing agent.
Being strong reducing agents, aldehydes reduce Fehling solution to red ppt. of cuprous oxide.
RCHO + 2Cu2+ + + Cu2O + 3H2O
B. Tollen’s Reagent Test (given only by reducing sugars)
Tollen’s reagent is an ammoniacal solution of silver nitrate and is prepared by adding NH4OH solution to AgNO3 solution till the ppts. Of Ag2O first formed just redissolve.
When an aldehyde is heated with Tollen’s reagent, the latter is reduced to metallic silver which deposits on the walls of the test tube.
2AgNO3 + 2NH4OH Ag2O + 2NH4NO3 + H2O
Ag2O + 4NH4OH 2[Ag(NH3)2]+ + 3H2O
C. Benedict’s Test (given only by reducing carbohydrates)
Benedict’s solution is alkaline solution containing citrate ions as complexing agent.
Aldehydes, on warming with this solution, give brick red precipitates.
RCHO + Cu2+ Cu2O + Oxidation Products
D. Iodine solution test (given only by starch)
Presence of starch is tested with iodine which gives blue-black colour with starch.
2. FATS AND OILS
Fats, oils and their derivatives found in living system belong to the class of substance called lipids. These are sparingly soluble in water but highly soluble in organic solvents. Fats and oils are glycerol esters of different fatty acids. For example, glyceride of unsaturated fatty acids like oleic acid [C17H33COOH] are called unsaturated fats and similarly glyceride of saturated fatty acids like Stearic acid [C17H35COOH] are called saturated fats. Unsaturated fats can be saturated by addition of hydrogen. This process is called hydrogenation. These are excellent sources of energy and fats on oxidation provide about twice as much as energy as that produced by carbohydrates . Important sources of fats & carbohydrates are peanuts, coconut, soyabean, butter, cottonseeds mustard, etc.
Identification Tests
A. Fats and oils have generally low melting points. If a fat is shaken with either ethanol or chloroform in a dry test tube, it dissolves giving a clear solution.
B. To the given oil or fat sample , add few crystals of potassium hydrogen sulphate (KHSO4). After heating, a pungent irritating odour due to the formation of acrolein confirms the presence of an oil or a fat.
The oil or fat on heating undergoes hydrolysis to give glycerol and fatty acids. The glycerol thus produced on strong heating undergoes dehydration to form acrolein which has irritating smell.
Oil or fat Glycerol + Fatty Acids
CH2OH CH2
CH2OH CH + 2H2O
CH2OH CHO
3. PROTEINS
Proteins are essential organic compounds for any living system to build and repair our body. Proteins are main constituents of muscles, blood, skin, hair and other body parts. Besides carbon, hydrogen and oxygen, other elements such as nitrogen and sulphur are in proteins. Proteins are made up of chains of amino acids and are very essential components of our food. Beans, pulses, fish, meat, milk, cheese, etc. are rich sources of proteins.
Identification Tests
A. Biuret Test
In this test, proteins when heated with strong alkaline copper sulphate (blue) give a violet or pink colour.
This test is meant for testing the compounds having having a CONH2 group called peptide linkage. As the proteins contain long chains of peptide linkages, they give positive biuret test by forming complex with Cu2+ ions.
B. Xanthoproteic test
To the protein sample, add few drops of conc. HNO3. A yellow precipitate confirms the presence of proteins.
This test is based upon the formation of yellow coloured aromatic nitro compounds which are produced by the action of nitric acid on the benzene rings present in some of the - amino acids (tyrosine, phenylamine, etc.) constituting the protein.
4. UNSATURATION
The unsaturation in the organic compounds is due to the presence of double or triple bonds in its constituent compounds.
Identification test
Sulphuric acid Test
In this test, the compound is taken in a clear test tube and conc. H2SO4 is added carefully dropwise. The contents are carefully shaken. The unsaturated compound dissolves in conc H2SO4 due to the formation of alkyl hydrogen sulphate (double bonds break to form single bonds).
C C + H2SO4 C C
5. HYDROXYL GROUP
The hydroxyl derivatives of the paraffins are termed as alcohols. These are produced by the replacement of one, two or more hydrogen atoms of paraffins by the corresponding number of hydroxyl groups. Alcohols are monohydric, dihydric, trihydric or polhydric depending upon the number of hydroxyl groups present in them. Alcohol and hydroxyl compounds are generally liquids and soluble in water because of the functional group which is capable of forming hydrogen bonds.
Identification Tests
A. ESTERIFICATION TEST
Alcohols react with carboxylic acids in presence of a few drops of conc. H2SO4 as catalyst to form esters. A pleasant fruity smell indicates the presence of an ester and hence the hydroxyl group.
RCOOH + CH3CH2OH RCOOCH2CH3 + H2O
6. ALDEHYDE GROUP
Identification Tests
A. Fehling’s solution Test
Fehling’s solution is an alkaline solution of copper sulphate containing sodium potassium tartrate (Rochelle salt) as the complexing agent.
Being strong reducing agents, aldehydes reduce Fehling solution to red ppt. of cuprous oxide.
RCHO + 2Cu2+ + + Cu2O + 3H2O
B. Tollen’s Reagent Test
Tollen’s reagent is an ammoniacal solution of silver nitrate and is prepared by adding NH4OH solution to AgNO3 solution till the ppts. Of Ag2O first formed just redissolve.
When an aldehyde is heated with Tollen’s reagent, the latter is reduced to metallic silver which deposits on the walls of the test tube.
2AgNO3 + 2NH4OH Ag2O + 2NH4NO3 + H2O
Ag2O + 4NH4OH 2[Ag(NH3)2]+ + 3H2O
C. Benedict’s Test
Benedict’s solution is alkaline solution containing citrate ions as complexing agent.
Aldehydes, on warming with this solution, give brick red precipitates.
RCHO + Cu2+ Cu2O + Oxidation Products
7. CARBOXYLIC GROUP
The organic compounds containing the carboxyl group ( C OH) as the functional group are called carboxylic acids. Acids containing one COOH group are termed monocarboxylic acids while others containing two or three COOH groups are called dicarboxylic and tricarboxylic respectively. These are normally soluble in water having pungent smell.
Identification tests :
A. Litmus Test
Dissolve a pinch of the organic compound in water in a test tube and add to it 2-3 drops of the blue litmus solution. If the blue litmus solution turns red, it shows the presence of a carboxyl group.
B. ESTERIFICATION TEST
Alcohols react with carboxylic acids in presence of a few drops of conc. H2SO4 as catalyst to form esters. A pleasant fruity smell indicates the presence of an ester and hence the carboxyl group.
RCOOH + CH3CH2COOH RCOOCH2CH3 + H2O
C. Sodium Bicarbonate test
Dissolve a pinch of the organic compound in water in a test tube . Add to it a few drops of aqueous NaHCO3 solution. If there is an effervescence due to the evolution of carbon dioxide, it shows the presence of a carboxyl group.
RCOOH + NaHCO3 RCOONa +CO2 + H2O
TEST FOR APPLE JUICE
TEST FOR COCUNUT WATER
TEST FOR TOMATO JUICE
RESULTS
CONCLUSION :
After analyzing the fruits and vegetable juices, the following opinion emerges about the compounds present in them.
CARBOHYDRATES : The carbohydrates are the main constituents of all the fruits and vegetable juices but are present in varying quantities.
FATS AND OILS : Fats are rarely found in fruits and vegetables. But in the present study, the two juices (apple and coconut) show the presence of fats but it is not found in case of tomato.
PROTEINS : Most of the fruits and vegetables contain proteins. In the present study, the coconut water and tomato juice did not show the presence of proteins.
UNSATURATION : Since each fruit and vegetable consists of carbohydrates, fats & proteins, the presence of double or triple bonds between carbon atoms is must. Therefore, almost all fruits and vegetables have unsaturated compounds.
HYDROXYL GROUP : This group is present in all the fruits and vegetable juices. But as compared to fruit juices, this group is present more in vegetable juices.
ALDEHYDE GROUP : Aldehydes are type of carbohydrates. They are present in almost all the juices in large or small quantities.
CARBOXYLIC ACID GROUP : It is also present in all the vegetables and fruit juices.