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by Procheta Mallik


Using some commonly available chemicals (sodium hydroxide and copper sulphate), one can create a solution that is a good indicator to detect the presence of protein in a food substance. Here, we perform the test on saltwater and milk.

Video Overview

    • Sodium Hydroxide (NaOH) is a highly reactive and caustic substance. Handle the flakes and solution with extreme care and caution

    • Extended skin contact with NaOH can lead to ulceration and scarring.

    • Gloves are compulsory while handling NaOH. Add water to NaOH flakes; not NaOH flakes to water. For every gram of flakes add a minimum of 10ml of water

    • Add copper sulphate solution drop by drop

    • Handle the breakable material carefully.

    • Please do not ingest any of the materials

  1. You may use transparent glasses instead of test tubes if the latter isn't available
    • You may use transparent glasses instead of test tubes if the latter isn't available

    • You may use egg instead of milk

    • Add 1 teaspoon (or pipette 5 ml) of milk into a test tube

    • Prepare a saltwater solution and add 1 teaspoon of salt water into another test tube

    • One of the plastic containers contains of copper sulphate crystals

    • Fill container with water, close it, and shake to dissolve the crystals

    • The other plastic container contains sodium hydroxide flakes

    • Fill the container with water, close it, and shake well to dissolve the flakes

    • Add 1 teaspoon (or pipette 5ml) of the sodium hydroxide solution to each of the test tubes; shake well

    • Add copper sulphate solution, drop by drop, to each of the test tubes

    • A deep violet colour would indicate the presence of protein

    • What is the colour inside the saltwater test tube?

    • What about the test tube with milk/egg?

    • Vary the proportion of ingredients in each of the test tubes and see if you get the same result

    • Test other household food items for protein using the same method: cooked rice, wheat flour mixed with water, vegetable stock, chicken/meat stock etc.

    • Can you research what chemical is produced to cause the purple colour?

    • Use the same quantity of ingredients as mentioned in the steps, except when experimenting with variations where indicated

    • Make sure the solutions are stirred and mixed well

    • Ensure the drops of copper sulphate solution mix well with the ingredients in the test tubes by gently shaking them while adding it

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