Question 13: Find out a qualitative test for proteins, fats and oils, amino acids and test any fruit juice, saliva, sweat and urine for them.
Answer:
(a) Test for protein
Biuret’s test – If Biuret’s reagent is added to protein, then the colour of the reagent changes from light blue to purple.
(b) Test for fats and oils
Grease or solubility test
(c) Test for amino acid
Ninhydrin test – If Ninhydrin reagent is added to the solution, then the colourless solution changes to pink, blue, or purple, depending on the amino acid.
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Item
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Name of the test
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Procedure
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Result
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Inference
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1.
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Fruit juice
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Biuret’s test
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Fruit juice + Biuret’s reagent
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Colour changes from light blue to purple
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Protein is present.
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Grease test
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To a brown paper, add a few drops of fruit juice.
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No translucent spot
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Fats and oils are absent or are in negligible amounts.
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Ninhydrin test
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Fruit juice + Ninhydrin reagent + boil for 5 minutes
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Colourless solution changes to pink, blue, or purple colour
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Amino acids are present.
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2.
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Saliva
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Biuret’s test
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Saliva + Biuret’s reagent
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Colour changes from light blue to purple
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Proteins are present.
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Grease test
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On a brown paper, add a drop of saliva.
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No translucent spot
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Fats/oils are absent.
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Ninhydrin test
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Saliva + Ninhydrin reagent + boil for 5 minutes
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Colourless solution changes to pink, blue, or purple colour
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Amino acids are present.
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3.
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Sweat
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Biuret’s test
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Sweat + Biuret’s reagent
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No colour change
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Proteins are absent.
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Solubility test
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Sweat + Water
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Oily appearance
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Fats/oil may be present.
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Ninhydrin test
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Sweat + Ninhydrin reagent + boil for 5 minutes
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No colour change, solution remains colourless
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Amino acids are absent.
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4.
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Urine
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Biuret’s test
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Few drops of urine + Biuret’s reagent
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Colour changes from light blue to purple
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Proteins are present.
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Solubility test
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Few drops of urine + Water
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Little bit of oily appearance
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Fats may or may not be present.
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Ninhydrin test
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Few drops of urine + Ninhydrin reagent + boil for 5 minutes
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Colourless solution changes to pink, blue, or purple colour depending on the type of amino acid
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Amino acids are present.
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