5 cm3 dilute sodium hydroxide solution and 5 cm3 one percent copper sulphate solution are added to a solution of food specimen. The purple colour which is o...

Answer Details

The purple colour observed after adding 5 cm3 dilute sodium hydroxide solution and 5 cm3 one percent copper sulphate solution to a solution of food specimen shows the presence of protein. This is because the Biuret test is used to detect proteins in a sample. In this test, the copper ions in the copper sulphate solution react with the peptide bonds in the protein molecule to form a purple complex. The intensity of the purple colour is directly proportional to the concentration of the protein present in the sample.