Question

a chemical that changes it's colour to indicate the presence of a chemical substance​

Answer 1

Answer:

Phenolphthalein is a universal indicator, which means it changes color to show the pH of certain solutions. Phenolphthalein stays colorless in acidic solutions and turns pink in alkaline solutions. Sodium hydroxide is a base, so when you add phenolphthalein, the solution turns pink. Other indicators commonly used in the laboratory are litmus and methyl orange. A Litmus indicator solution goes red in acidic solutions, blue in alkaline solutions and purple in neutral solutions. Methyl orange turns red in acidic solutions and yellow in neutral or alkaline solutions.

Starch and Iodine Solutions

The starch test is a chemical reaction that determines whether starch amylose is present in a substance. When you add starch to iodine in water, it creates a starch/iodine complex with an intense blue color. To test whether starch is present in a foodstuff, mix a solution of iodine and potassium iodide in water. The solution has a light orange-brown color, but when you apply it directly to a sample that contains starch (such as potatoes or bread), it turns a blue-black color.

Hydrated Copper Carbonate

When copper reacts with the elements (oxygen, water and carbon dioxide), it turns from its element color of reddish-brown to green. This chemical reaction is hydrated copper carbonate, and a famous example of it is the Statue of Liberty. Built in 1886, the Statue of Liberty was initially reddish-brown. Over time, its copper plates underwent a chemical reaction. The same things can happen to copper pennies. A similar reaction occurs when iron rusts: Iron oxide forms on its surface (oxidation) causing the iron to turn a reddish color.

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