NCERT Grade 7-Physical and Chemical Changes-Questions

NCERT Solutions for Class 7 Science

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Physical and Chemical Changes

1.     Classify the changes involved in the following processes as physical or chemical changes:

(a) Photosynthesis

(b) Dissolving sugar in water

(c) Burning of coal

(d) Melting of wax

(e) Beating aluminum to make aluminum foil.

(f) Digestion of food

2.    State whether the following statements are true or false. In case a statement is false, write the corrected statement in your notebook.

(a) Cutting of log of wood into pieces is a chemical change. (True/False)

(b) Formation of manure from leaves is a physical change. (True/False)

(c) Iron pipes coated with zinc do not get rusted easily. (True/False)

(d) Iron and rust area same substance. (True/False)

(e) Condensation of steam is not a chemical change. (True/False)

3.    Fill in the blanks in the following statements:

(a) When carbon dioxide is passed through lime water, it turns milky due to formation of——.

(b) The chemical name of baking soda is——-

(c) Two methods by which rusting of iron can be prevented are—– and—–.

(d) Changes in which only——– properties of a substance change are called physical changes.

(e) Changes in which new substances are formed are called——-

4.    When baking soda is mixed with lemon juice, bubbles are formed with the evolution of a gas. What type of change is it? Explain.

5.    When candle burns, both physical and chemical changes take place. Identify these changes. Give another example of familiar process in which both the chemical and physical changes take place.

6.    How would you show that setting of curd is a chemical change?

7.    Explain why burning of wood and cutting it into small pieces are considered as two different types of changes.

8.    Describe how crystals of copper sulphate are prepared.

9.    Explain how painting of an iron gate prevents it from rusting.

10.  Explain why rusting of iron objects is faster in coastal areas than in deserts.

11.  The gas we use in the kitchen is called liquefied petroleum gas (LPG). In the cylinder it exists as liquid. When it comes out from the cylinder it becomes a gas (change A) then it burns (change B). The following statement s are pertain to these changes. Choose the correct one.

(i) Process – A is a chemical change.

(ii) Process -B is chemical change.

(iii) Both processes A and B is a chemical changes.

(iv) None of these processes is a chemical change.

12.  Aerobic bacteria digests animal waste and produce biogas (change -A).The biogas is then burnt as fuel(change-B). The following statements pertain to these changes. Choose the correct one.

(i) Process – A is a chemical change.

(ii) Process – B is a chemical change.

(iii) Both processes A and B are chemical changes.

(iv) None of these process is a chemical changes.

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