NCERT Grade 7-Physical and Chemical Changes-Answers – MySchoolPage

NCERT Grade 7-Physical and Chemical Changes-Answers

NCERT Solutions for Class 7 Science

Find 100% accurate solutions for NCERT Class VII Science. All questions have been explained and solved step-by-step, to help you understand thoroughly. Free Download option available!

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1.    (a) Chemical change

(b) Physical changes

(c) Chemical change

(d) Physical change

(e) Physical change

2.    (a) False- cutting a log of wood into pieces is a physical change.

(b) False- formation of manure from leaves is a chemical change.

(c) True

(d) False- Iron and rust are different substances.

(e) True

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 calcium carbonate.

(b) The chemical name of baking soda is sodium hydrogen carbonate.

(c) Two methods by which rusting of iron can be prevented are painting and

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

(e) Changes in which new substances are formed are called chemical

4.    It is a chemical change. Here, a new substance, carbon dioxide is formed..

5.    The wax of the candle first melt then vaporizes and burns.

Melting f wax is a physical change since melted wax can be solidified back to the wax and there is not new substance is formed.

When wax burns, smoke and carbon dioxide is formed which are new substance. So, it is a chemical change.

Lightening of bulb using a dry cell is a chemical as well as physical change. Chemical reaction inside the dry cell produce current and lighting is conversion of electrical energy to light energy.

6.    When some sour substance is added to milk or kept overnight, it turns into curd. The curd is no way can be converted into milk. Curd is a different substance than So, formation of curd is a chemical change.

7.    Burning of wood produces ash and smoke. Hence the properties of wood are changed and new substances are formed. So, it is a chemical change.

When a log of wood is cut into small pieces, there is no new substance formed. Each small piece bears the properties of wood. So, it is a physical change. Obviously, burning and cutting of wood are two different types of changes.

8.    A cup of water is taken in a beaker and a few drops of dilute Sulphuric acid are added into it. The water is heated. When it start boiling copper sulphate powder is added slowly while stirring continuously till no more powder can be dissolved. The solution is filtered and allowed to cool down. Crystal of Copper sulphate slowly forms at the bottom of the beaker.

9.    For rusting, iron must be in contact with both air and moisture. When iron gate is painted the layer of paint cuts the contact between air, moisture and iron. Thus, it prevents rusting.

10.  In coastal areas there is more moisture in air due to the presence of sea. But, in desert there is a scarcity of water and hence air is almost dry there. Both air and moisture are necessary conditions for rusting. So, rusting is faster is coastal areas than in desert.

11.   (ii) Process -B is a chemical change.

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

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