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Add the food colouring.
Put the solution on a Petri dish, covering the whole surface with a glass stick. Leave it dry.

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Measure the pH of the solution with a litmus test. If the pH is acid, it will turn into red. Add the NaOH solution, drop by drop and shaking, until the pH will be neutral and the the litmus test be green.

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Warm the blend up on an electric plate, let it boil for 15 minutes. Notice the variation of colour into transparent. Cover the beaker not to make the liquid evaporate.

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Put 25ml of distilled water in a beaker, then add 2,5g of starch in order to obtain a fluid but thick blend.
Add 3ml of HCl and 3ml of glycerol to the blend, gently shaking it.

# data[].attributes.body
1) Distilled water
2) Commercial starch
3) 3ml of HCl 0,1M
4) 3ml of glycerol
5) 3ml of NaOH 0,1M
6) Food colouring

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Add the sodium hydroxide solution and the copper sulphate in every test tubes.
In the one containing water, the liquid keeps the blue color of copper.
In the test tubes containing food, if they have proteins, the colour will turn into violet, due to the reaction between proteins and copper.
If the food does not have proteins, it will keep the blue colour.

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1) Put water inside the first test tube
2) Put water and salt in the second one
3) Put different types of food in the other test tubes

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1) Test tubes
2) Sodium hydroxide solution at 10%
3) Copper sulphate solution at 1%
4) Milk
5) Salt
6) Cheese
7) Egg yolk
8) Meat