NCERT Solutions for 7th Class Science: Chapter 6-Physical and Chemical Changes
NCERT Solutions for 7th Class Science: Chapter 6-Physical and Chemical Changes

Class 7: Science Chapter 6 solutions. Complete Class 7 Science Chapter 6 Notes.

NCERT Solutions for 7th Class Science: Chapter 6-Physical and Chemical Changes

NCERT 7th Science Chapter 6, class 7 Science Chapter 6 solutions

Page No: 65

Exercises

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

Answer

(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

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)

Answer

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. Rust is oxide of iron (Fe2O3)

(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 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

(a) When carbon dioxide is passed through limewater, it turns milky due to the formation of calcium carbonate (CaCO3).

(b) The chemical name of baking soda is sodium hydrogen carbonate (NaHCO3).

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

(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.

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.

Answer

When baking soda is mixed with lemon juice, the bubbles which are formed with the evolution of a gas is due to the evolution of carbon dioxide gas. Since, there is formation of a new substance in this reaction, it is a chemical change.

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.

Answer

When a candle burns, both physical and chemical changes take place.

The melting wax is physical change as there is no formation of new product.

The burning of wax is chemical change as light is lit up by consuming the energy from wax.

Cooking of food is both physical and chemical because raw vegetables get cooked which is a chemical change and the water changes into steam which is a physical change.

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

Answer

The curd is formed from milk. Both curd and milk have different properties. Also, once the curd is formed it cannot be reversed back into milk. So, there is formation of new substance with different properties and also an irreversible process, setting of curd is a chemical change.

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

Answer

When we burn wood, it turns into ashes which is a new substance and process is irreversible one, hence is a chemical change. While cutting the wood into small pieces no new substance is formed, hence is a physical change.

8. Describe how crystals of copper sulphate are prepared.

Answer

Crystals of copper sulphate are prepared by the method of crystallization.

The process is as followed:

Step 1: A cupful of water in a beaker is taken.

Step 2: Few drops of dilute sulphuric acid is added to it.

Step 3: Water is heated and when it starts boiling copper sulphate powder is added slowly while    stirring till no more copper sulphate powder dissolved in it.

Step 4 : Solution is filtered and let it cool without disturbance. After some time the crystals of copper can be observed in it.

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

Answer

Painting of an iron gate prevents it from rusting because it cut the direct contact of iron from the environment and therefore there is no further exposure of iron to oxygen in moisture which is the causes for rusting.

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

Answer

Iron objects get rusted because of the reaction with oxygen present in moist air. In coastal areas, the presence of moisture is more because of sea or ocean while in deserts the air is dry and hot. Therefore, rusting of iron objects is faster in coastal areas than in deserts due to presence of moisture.

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.

Answer

(ii) Process – B is a chemical change.

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.

Answer

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

NCERT 7th Science Chapter 6, class 7 Science Chapter 6 solutions

NCERT Solutions for 7th Class Science: Chapter 6: Download PDF

NCERT Solutions for 7th Class Science: Chapter 6-Physical and Chemical Changes

Download PDF: NCERT Solutions for 7th Class Science: Chapter 6-Physical and Chemical Changes PDF

Chapter-wise NCERT Solutions Class 7 Science

Chapter 1 Nutrition in Plants
Chapter 2 Nutrition in Animals
Chapter 3 Fibre to Fabric
Chapter 4 Heat
Chapter 5 Acids, Bases and Salts
Chapter 6 Physical and Chemical Changes
Chapter 7 Weather, Climate and Adaptations of Animals to Climate
Chapter 8 Winds, Storms and Cyclones
Chapter 9 Soil
Chapter 10 Respiration in Organisms
Chapter 11 Transportation in Animals and Plants
Chapter 12 Reproduction in Plants
Chapter 13 Motion and Time
Chapter 14 Electric Current and Its Effects
Chapter 15 Light
Chapter 16 Water: A Precious Resource
Chapter 17 Forests: Our Lifeline
Chapter 18 Wastewater Story


About NCERT

The National Council of Educational Research and Training is an autonomous organization of the Government of India which was established in 1961 as a literary, scientific, and charitable Society under the Societies Registration Act. Its headquarters are located at Sri Aurbindo Marg in New Delhi. Visit the Official NCERT website to learn more.