# NCERT Solutions for Class 7 Science Chapter 6 Physical And Chemical Changes

Written by Team Trustudies
Updated at 2021-02-11

## NCERT solutions for class 7 Science Chapter 6 Physical And Chemical Changes Exercise

Q.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 aluminium to make aluminium foil
(f) Digestion of food

NCERT Solutions for Class 7 Science Chapter 6 Physical And Chemical Changes

(a) Photosynthesis $?$ chemical change
(b) Dissolving sugar in water $?$ physical change
(c) Burning of coal $?$ chemical change
(d) Melting of wax$?$ physical change
(e) Beating aluminium to make aluminium foil $?$ physical change
(f) Digestion of food$?$ chemical change

Q.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 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)

NCERT Solutions for Class 7 Science Chapter 6 Physical And Chemical Changes

(a) Cutting a log of wood into pieces is a chemical change. (True)
(b) Formation of manure from leaves is a physical change. (False)
(c) Iron pipes coated with zinc do not get rusted easily. (True)
(d) Iron and rust are the same substances. (False)
(e) Condensation of steam is not a chemical change. (True)

Q.3 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.

NCERT Solutions for Class 7 Science Chapter 6 Physical And Chemical Changes

(a) When carbon dioxide is passed through lime water, it turns milky due to the 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 galvanization__.
(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__ changes.

Q.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.

NCERT Solutions for Class 7 Science Chapter 6 Physical And Chemical Changes

This is a chemical change.
Lemon juice + Baking soda $?$Carbon dioxide + other substances

Q.5 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.

NCERT Solutions for Class 7 Science Chapter 6 Physical And Chemical Changes

When a candle burns, both physical and chemical changes take place.
Physical change : Melting of wax
Chemical change : Burning of wax
Eating of food is another example where both physical and chemical changes occur simultaneously.
Physical change : Breaking down of larger food particles into smaller particles
Chemical change : Digestion of food

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

NCERT Solutions for Class 7 Science Chapter 6 Physical And Chemical Changes

Once the curd is formed, milk cannot be re-obtained from it. Also, both milk and curd have different properties. Since these are the properties of a chemical change, hence, the setting of curd is a chemical change.

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

NCERT Solutions for Class 7 Science Chapter 6 Physical And Chemical Changes

When we burn wood, a new substance, coal, is formed. Therefore, it is a chemical change. However, when we cut wood, only the shape and size of the wood are changed. No new substance is formed. Therefore, it is a physical change.

Q.8 Describe how crystals of copper sulphate are prepared.

NCERT Solutions for Class 7 Science Chapter 6 Physical And Chemical Changes

Crystals of copper sulphate are prepared by the method of crystallization. The process is as follows. A cupful of water is taken in a beaker. Few drops of dilute sulphuric acid are added to this. The water is then heated and when it starts boiling, copper sulphate powder is added with stirring. Copper sulphate powder should be added on till the solution becomes saturated. It is then filtered into a china dish and allowed to cool. The solution should be kept undisturbed. Slowly, the crystals of copper sulphate separate out.

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

NCERT Solutions for Class 7 Science Chapter 6 Physical And Chemical Changes

Rusting is aided by both moisture (water) and air (oxygen). By painting an iron gate, we prevent its contact from the air and moisture present in the atmosphere. Hence, rusting is prevented.

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

NCERT Solutions for Class 7 Science Chapter 6 Physical And Chemical Changes

As content of moisture in the air in coastal areas is higher than in the air in deserts. So, the process of rusting is faster in coastal areas.

Q.11 The gas we use in the kitchen is called liquified petroleum gas (LPG). In the cylinder it exist 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.
(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 processes is a chemical change

NCERT Solutions for Class 7 Science Chapter 6 Physical And Chemical Changes

(ii) Process – B is a chemical change.

Q.12 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.
(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 processes is a chemical change

NCERT Solutions for Class 7 Science Chapter 6 Physical And Chemical Changes