NCERT Solutions for Class 7 Science Chapter 6 – Physical and Chemical Changes, contains solutions to various questions in Exercise for Chapter 6. At the end of the Solutions, all the keywords and Notes which are important to understand Science Chapter 6 Physical and Chemical Changes, have been explained in a simple and easy to understand manner. NCERT Solutions for Class 7 help to check the concept you have learnt from detailed classroom sessions and the application of your knowledge.
| Category | NCERT Solutions for Class 7 |
| Subject | Science |
| Chapter | Chapter 6 – Physical And Chemical Changes |
Download NCERT Solutions for Class 7 Science Chapter 6 – Physical and Chemical Changes
NCERT Solutions for Class 7 Science Chapter 6- Physical and Chemical Changes– Solutions to Question 1 and Question 2
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 1:-
(a) Chemical change
(b) Physical change
(c) Chemical change
(d) Physical change
(e) Physical change
(f) 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 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
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.
NCERT Solutions for Class 7 Science Chapter 6 – Physical and Chemical Changes – Video Explanation
Answer 3:-
(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 galvanisation.
(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
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:-
It is a chemical change. Baking soda is a type of alkali and lemon juice contains acid. When the two of them are mixed together, they react and produce salt, water and carbon dioxide that is liberated in the form of bubbles. The changes in which new substances are produced are called chemical changes hence, it is a chemical change.
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 5:-
When a candle burns the melting and vaporisation of wax of candle is a physical change and combustion of the wax vapours in air is chemical change.
Another example of such a process is chewing of food. When we chew the food, its shape and form changes which is a physical change and the saliva breaks down the complex glucose molecules into simpler substances which is a chemical change.
Question 6:-
How would you show that setting of curd is a chemical change?
Answer 6:-
Setting of curd is a chemical change because curd is a different substance than milk. When milk is acted upon by lactobacillus bacteria, it changes to form curd. We cannot retrieve milk back from curd. Hence, setting of curd is a chemical change.
Question 7:-
Explain why burning of wood and cutting it into small pieces are considered as two different types of changes.
Answer 7:-
Burning of wood is a chemical change because it produces smoke. Wood cannot be retrieved back from smoke and the chemical composition of smoke is different from wood.
Cutting wood into small pieces is a physical change because we cannot retrieve the same log of wood from cut pieces but there is no difference in the chemical composition of pieces of wood anda log of wood.
Question 8:-
Describe how crystals of copper sulphate are prepared.
Answer 8:-
The crystals of copper sulphate can be prepared by the process of crystallisation
The steps are –
- Take a beaker and fill it with water. Add a few drops of dilute sulphuric acid in the water. Heat the water.
- Now add copper sulphate powder in it, when it starts boiling, with slow and constant stirring.
- Continue adding the powder until no more copper sulphate can dissolve in the solution.
- Now leave it undisturbed to cool down. As it cools down we will notice after some time the crystals of copper sulphate in the beaker.
Question 9:-
Explain how painting of an iron gate prevents it from rusting.
Answer 9:-
For rusting of iron, oxygen and moisture are required. Painting the iron gate will prevent the air and moisture to come in contact with iron and thereby will prevent rusting of iron.
Question 10:-
Explain why rusting of iron objects is faster in coastal areas than in deserts.
Answer 10:-
For rusting the presence of oxygen and moisture is essential. Coastal areas have humid climate which means that the air in these regions has high moisture content whereas deserts have little water therefore air in these regions is dry. Hence rusting occurs faster in coastal area 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 11:-
(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 12:-
(iii) Both processes A and B are chemical changes.
Topics Covered in Chapter 6 Physical and Chemical Changes Class 7 Science:-
- Physical Changes
- Chemical Changes
- Rusting of Iron
- Crystallisation
Important Terms Relevant to understand NCERT Solutions for Class 7 Science Chapter 6- Physical and Chemical Changes: –
Chemical change: The change which is characterised by the formation of new substances is called a chemical change. For example, the burning of coal
Chemical reaction: A process that changes the chemical composition of substances and produces a new substance is called a chemical reaction
Crystallisation: The process of formation of crystals of substances from their solutions is called crystallisation.
Galvanisation: The process of depositing a layer of zinc on iron to prevent it from rusting is called galvanisation.
Physical change: The change that is characterised by change in the physical state of a substance is called physical change. For example – melting of ice.
Rusting: The chemical change that occurs on iron surfaces exposed to moisture and oxygen which results in corrosion of iron is called rusting.
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