Question

Explain indicators of a chemical change with examples.

Answer 1

1. Take some broken pieces of eggshell in a test tube and add lemon juice to it. You could see bubbles of carbon-di-oxide evolving in the test tube. This is because of the chemical change between the two. Hence, we can say that evolution of bubbles serves as an indicator of a chemical change.
2. When water is added to quicklime (calcium oxide) there will be an evolution of a lot of heat along with the formation of slaked lime (calcium hydroxide). This is a chemical change and it is indicated by the evolution of heat when the reaction sets in between quicklime and water.
3. Spoilage of food is a chemical change and it is indicated by the foul smell. So, a change in odour is also an indicator of a chemical change.
4. When an iron nail is kept in water for a few days and taken out, the nail will become reddish-brown in colour indicating that it has rusted. Rusting is a chemical change and it is indicated by a change in colour of the iron nail.
5. A lump of curd is the precipitate that is obtained by the chemical reaction between hot milk and lemon juice. So, the formation of a precipitate is also an indication of a chemical change.