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NCERT solutions Science Textbook for Class 7 chapter 6 Physical and Chemical Changes

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Chapter 6 - Physical and Chemical Changes

Pages 65 - 66

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

Photosynthesis

Dissolving sugar in water

Burning of coal

Melting of wax

Beating aluminium to make aluminium foil

Digestion of food

Q 1 | Page 65 | view solution

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

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

Q 2.1 | Page 65 | view solution

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

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

Q 2.2 | Page 65 | view solution

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

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

Q 2.3 | Page 65 | view solution

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

Iron and rust are the same substances. (True/False)

Q 2.4 | Page 65 | view solution

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

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

Q 2.5 | Page 65 | view solution

Fill in the blanks in the following statements:

When carbon dioxide is passed through lime water, it turns milky due to the formation of _________.

Q 3.1 | Page 66 | view solution

Fill in the blanks in the following statements:

The chemical name of baking soda is _________.

Q 3.2 | Page 66 | view solution

Fill in the blanks in the following statements:

Two methods by which rusting of iron can be prevented are _________ and ____ _

Q 3.3 | Page 66 | view solution

Fill in the blanks in the following statements:

Changes in which only _____ __ properties of a substance change are called physical changes.

Q 3.4 | Page 66 | view solution

Fill in the blanks in the following statements:

Changes in which new substances are formed are called _________changes

Q 3.5 | Page 66 | view solution

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

Q 4 | Page 66 | view solution

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.

Q 5 | Page 66 | view solution

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

Q 6 | Page 66 | view solution

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

Q 7 | Page 66 | view solution

Describe how crystals of copper sulphate are prepared.

Q 8 | Page 66 | view solution

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

Q 9 | Page 66 | view solution

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

Q 10 | Page 66 | view solution

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

1) Process − A is a chemical change

2) Process − B is a chemical change.

3) Both processes A and B are chemical changes.

4) None of these processes is a chemical change

Q 11 | Page 66 | view solution

Anaerobic bacteria digest 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.

1) Process − A is a chemical change.

2) Process − B is a chemical change.

3) Both processes A and B are chemical changes

4) None of these processes is a chemical change

Q 11 | Page 66 | view solution

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