Question

Find out any qualitative test for proteins, fats, and oils, amino acids. Test any fruit juice, saliva, sweat and urine for them.

Answer 1

Hint: Change of light blue colour to purple confirms the presence of proteins, formation of white milky emulsion confirms the presence of fats and oils and change of colourless solution into pink, blue or purple confirms the presence of amino acids.

Complete answer:
1. Qualitative test for protein:
Biuret test: When biuret's reagent is added to the protein then the colour change of the reagent is found to be light blue to purple.

> Test for fruit juice, saliva, sweat and urine:
- Biuret test for Fruit Juice : When the biuret's agent is added in the fruit juice then colour change from light blue to purple is observed which confirms the presence of protein in it.
- Biuret test for Saliva: When the biuret's agent is added to saliva then colour change from light blue to purple is observed which confirms the presence of protein in it.
- Biuret test for Sweat: When the biuret's agent is added to sweat then no colour change is observed which confirms the absence of protein in it.
- Biuret test for Urine: When the biuret's agent is added to urine then colour change from light blue to purple is observed which confirms the presence of protein in it.

2. Qualitative test for fats and oils:
Emulsion test: In this test, ethanol is added to the substance which needs to be tested and after addition of ethanol shake them in order to dissolve. Then, dilute it to obtain clear liquid and then take another test tube, add water in it and then pour the ethanolic solution. A white milk like emulsion is observed which indicates the presence of fats or oils.

> Test for fruit juice, saliva, sweat and urine:
- Grease test for Fruit juice: Add a few drops of fruit juice to a brown paper then no translucent spot is observed which confirms that there is absence of fats and oils or they are present in negligible amounts.
- Grease test for Saliva: Add a few drops of saliva to a brown paper then no translucent spot is observed which confirms that there is absence of fats and oils or they are present in negligible amounts.
- Solubility test or Sweat: When sweat and water are mixed then there is oily appearance observed which confirms the presence of fats or oils.
- Solubility test for Urine: When urine and water are mixed then there is little bit of oily appearance observed which means there may or may not be the presence of fats or oils.

3. Qualitative test for amino acid:
Ninhydrin test- Ninhydrin reagent is added to the fruit juice and boiled for 5 minutes then the colourless solution turns pink, blue or purple and this change in colour indicates the presence of amino acids.

> Test for fruit juice, saliva, sweat and urine:
- Ninhydrin test for Fruit juice: The ninhydrin agent is added to fruit juice and boiled for 5 minutes then the colourless solution changes to pink, blue, or purple colour which confirms the presence of amino acid in it.
- Ninhydrin test for Saliva: The ninhydrin agent is added to saliva and boiled for 5 minutes then the colourless solution changes to pink, blue, or purple colour which confirms the presence of amino acid in it.
- Ninhydrin test for Sweat: The ninhydrin agent is added to sweat and boil for 5 minutes then no colour change is observed which confirms the absence of amino acid in it.
- Ninhydrin test for Urine: The ninhydrin agent is added to urine and boils for 5 minutes then the colourless solution changes to pink, blue, or purple colour according to the type of amino acid present and it confirms the presence of amino acid in it.

Note: Qualitative test for proteins, fats, and oils, amino acids are Biuret test, Emulsion test and Ninhydrin test respectively and there is change of light blue to purple colour seen in the biuret test, white milk like emulsion is seen in emulsion test and change of colourless solution into pink, blue or purple is seen in Ninhydrin test.