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

NCERT Solutions Class 7 Science Chapter 6 Physical and Chemical Changes is provided here to help students in understanding the topic thoroughly. All these solutions are solved by experts with a detailed explanation. Class 7 NCERT Solutions for Science Chapter 6 includes all the textbook exercise questions and answers. These solutions will help students complete their assignments & homework.

NCERT Solutions for Class 7 Science Chapter 6 Questions and Answers

Exercise Questions

Question 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

Question 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:
(a) False
(b) False
(c) True
(d) False
(e) True

Question 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 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.

Question 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 4:  This a chemical change as new products are formed.

Lemon juice + Baking soda → Carbon dioxide + other substances

When acid react with carbonates, salt is formed releasing carbon dioxide and water.

Question 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.

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

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

Answer 6: Setting of curd is a chemical change since a new substance (lactic acid) is formed which differs in taste from the original substance (fats and proteins) i.e. milk. Also the change is irreversible (curd cannot be converted into milk).

Question 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, 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.

Question 8: Describe how crystals of copper sulphate are prepared.

Answer: Crystals of copper sulphate are prepared as follows:

  • Take a water in a beaker and add a few drops of dilute sulphuric acid.
  • Heat the water. When it starts boiling add copper sulphate powder slowly with continuous stirring.
  • Continue adding copper sulphate powder till saturation level.
  • Filter the solution and left for cooling.
  • Leave undisturbed the solution when it is cooling.
  • We can observe the crystals of copper sulphate after few hours.

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

Answer: For rusting, the presence of both oxygen and water (or water vapour) is required. The coat of the paint prevents direct contact of iron with air and oxygen and thus prevents it from rusting.

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

Answer: Rusting of iron requires contact with water(moisture) and oxygen. In coastal areas, humidity is more in comparison to that in deserts; hence, rusting of iron objects is faster in coastal areas than in deserts.

Question 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.

Question 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.

Having a good grasp over CBSE NCERT Solutions for Class 7 Science will further help the students in their preparation for board exams and other competitive exams. NCERT Solutions for Class 7 Science Chapter 6 Physical and Chemical Changes provided by CBSE Path help students to clear their doubts and to obtain good marks in the exams. All the solutions provided in this article are strictly based on the CBSE syllabus and curriculum.

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