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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

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  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

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    • One of the plastic containers contains of copper sulphate crystals

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

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    • The other plastic container contains sodium hydroxide flakes

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


    1) Need one photo for each step

    2) How would children know pH is 12 or 13? If you want them to do litmus test, say that otherwise specify how much NaOH to be dissolved in how much water.

    Procheta Mallik - Reply

    • 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

    Comment by vishal:

    1) Add label to each test tube in last photo

    2) Don't change the order - previous photo has milk to left and salt to the right.

    Procheta Mallik - Reply

    • 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?

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    • 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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Finish Line

Suchitha Vishwa

Member since: 05/02/2017

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30 Guides authored


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30 Guides authored


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