Question

E. Answer the following questions in detail.
1. When a candle burns, both physical and chemical change take place. How?
2. Setting of curd is a chemical change. Explain.
3. What do you observe when you mix vinegar and baking soda? How do you
perform a test for the evolving gas?
4. Describe how crystals of copper sulphate are prepared.
5. Which of the changes given below are chemical changes? Give reasons for your
answers.
a. Cutting grass b. Burning toast c. Making tea with a tea bag and water d. Frying an
egg e Combustion of petrol in a car f. Ironing of clothes g. Preparing custard from
milk h. Drying wet hair
6. An iron nail is taken to the moon. Another is kept near the Gateway of India,
Mumbai, while the third one is kept near the Red Fort, Delhi. Compare the degree
of rust formation on the three nails.
7. The liquified petroleum gas (LPG) is the gas which is used for cooking at home. In
the cylinder it comes as a liquid. When it comes out from the cylinder it become a
gas (Change A). Then it burns (Change B). What are the differences between change
A and B?
C
The decomposition of animal waste by anaerobic bacteria produces biogas
(Change A). The biogas is then burnt as fuel (Change B). What are the similarities
between the two changes.
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Answer 1

Answer 1.

candle burns two changes take place simultaneously.

1. The minor changes that small amount of wox melts due to the heat of the flame .No new substance is formed in this process, hence this is a physical change.

2. the major change is the burning of wax which produces carbon dioxide , soot and water this is a chemical change.

√

therefore the melting of wax is a physical change but the burning of wax is a chemical change.

answer 2.

in the setting of curd milk changes into new substances , curd formation of new substance and irreversible process shows that setting of curd is a chemical change.

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Answer 2

Explanation:

Answer :

The minor change it amount of wax.