In an experiment, Radha took small amounts of an unknown food item in a test tube. Then, she added two drops of copper sulphate solution in the test tube along with a few drops of caustic soda solution. After a few minutes, the color of the food item changed to violet. In the given experiment, the change in color of the food item to violet indicates the presence of

Answer
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Hint: When caustic soda and copper sulphate solution are mixed in a test tube, the colour changes to violet. This test is used to determine how much protein is contained in food molecules. Caustic soda raises the pH, causing the colour to shift from blue to violet.

Complete answer:
The presence of proteins in the food item is shown by the change in colour to violet with the addition of copper sulphate and caustic soda solution.

Additional information:
Egg becomes violet when two drops of copper sulphate and ten drops of caustic soda or NaOH are put to it. This shows that proteins are present. This is Biuret's test, and the concept is straightforward. \[C{u^{2 + }}\]ions are reduced to \[C{u^ + }\] and attach to the egg proteins in the presence of alkaline media (caustic soda or NaOH), resulting in a violet tint.
The steps for testing the presence of proteins in a food item are as follows:
To test, make a paste or powder of the food.
In a test tube, put a tiny amount of the food item, 10 drops of water, and shake it. Toss in 2 drops of copper sulphate solution.
Shake the test tube well after adding 10 drops of caustic soda solution.

Note:
Always remember caustic soda and copper sulphate solution will give violet solution. The violet color along with the elements signifies the presence of proteins only.