science - physical and chemical changes

Class 7 - Science

Physical and Chemical Changes

Q&A
Question:

Describe how crystals of copper sulphate are prepared.

Answer:

Take a cupful of water in a beaker and add a few drops of dilute sulphuric acid. Heat the water. When it starts boiling, add copper sulphate powder slowly. Continue to add copper sulphate powder till no more powder can be dissolved. .During this process continuously stir the solution. Filter the solution. Leave it for cooling. Look it after some time, you can see the crystals of copper sulphate
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Questions and Answers


Physical and Chemical Changes - Questions
1.

Describe how crystals of copper sulphate are prepared.


Answer
2.

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 aluminium to make aluminium foil
(f) Digestion of food


Answer
3.

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


Answer
4.

(a) Cutting a 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 are the same substances. (True/ False)
(e)Condensation of steam is not a chemical change. (True/ False)


Answer
5.

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


Answer
6.

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


Answer
7.

Fill in the blanks in the following statements:
(a) When carbon dioxide is passed through lime water, it turns milky due to the 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 _____________ changes..


Answer
8.

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


Answer
9.

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


Answer
10.

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


Answer
11.

Explain how painting of an iron gate prevents it from rusting?


Answer
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