Here are important questions from chapter 6 of NCERT class 7 Science ‘Physical and Chemical Changes’. Textbook solutions of this chapter can be found here.

1. Change can be ………………………. or …………………………

Physical, chemical

2. What are physical properties?

Properties such as shape, size, colour and state of a substance are called its physical properties.

3. What is a physical change?

A physical change is a change in which a substance undergoes a change in its physical properties.

4. Physical changes are usually ……………………………..

Reversible

5. Give a common example of a familiar chemical change

Rusting of iron

6. What is rusting?

Rusting is the process by which a piece of iron left in the open acquires a film of brownish substance. This substance is called rust and this process is called rusting.

7. What substance is formed when a strip of magnesium is burned?

Magnesium oxide

8. When magnesium oxide is dissolved in water, we get …………………………….

Magnesium hydroxide

9. When a piece of iron is dropped into a copper sulphate solution why does its colour change from blue to green?

The colour of the solution changes from blue to green due to the formation of iron sulphate.

10. What is brown deposit on the iron nail dropped into the copper sulphate solution?

The deposit on the iron nail is copper.

11. When carbon dioxide passes through lime water, ………………………….. is formed?

Calcium carbonate

12. What is the chemical formula of calcium carbonate?

CaCO3

13. The reaction of copper sulphate with iron produces …………………………….

Iron sulphate and copper

14. What turns lime water milky?

Carbon dioxide

15. What is a chemical change?

A chemical change is a change in which one or more new substances are formed.

16. What layer protects us from the harmful ultraviolet radiation of the sun?

Ozone layer

17. For rusting to take place, the presence of both ………………………. and ………………………… is necessary.

water and oxygen

18. How can iron articles be protected from rusting?

Rusting takes place when iron articles come in contact with oxygen and water. By simply applying a coat of paint or grease on iron articles, rusting can be prevented.

19. What is galvanization?

Galvanization is the process of depositing a layer of zinc on iron to protect it from rusting.

20. How is stainless steel formed?

Stainless steel is formed by mixing iron with carbon and metals like chromium, nickel and manganese.

21. What is crystallization?

Crystallization is the process by which large crystals of pure substances can be obtained from their solutions.

Class 7 Science Solutions

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