NCERT Solutions For Class 7 Science Chapter 6 : Physical And Chemical Changes

NCERT Solutions For Class 7 Science Chapter 6 – Physical and Chemical Changes available in PDF. Students who want to score good marks in Class 7 examinations should solve the NCERT questions provided at the end of each chapter. Sometimes the NCERT questions are directly asked in the school examinations, which will be an added advantage for those students who practised the NCERT Solutions.

Along with the textbook solutions, students can also find some important questions, revision notes and other facts about the different types of changes. Class 7 NCERT Solutions for Chapter 6 Physical and Chemical Changes can be used for both class assignments, finals and also for Olympiad exams.

Download PDF of NCERT Solutions for Class 7 Science Chapter 6 – Physical and Chemical Changes

Access Answers of NCERT Solutions for Class 7 Science Chapter 6 – Physical and Chemical Changes

Exercise Questions

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

Solution:

a) Chemical change

b) Physical Change

c) Chemical change

d) Physical Change

e) Physical Change

f) 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)

Solution:

a) False

b) False

c) True

d) False

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.

Solution:

(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.

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.

Solution:

When baking soda is mixed with lemon juice, bubbles are formed with the evolution of a carbon dioxide gas. This is a chemical change.

Lemon juice + Baking soda → Carbon dioxide + other substances

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.

Solution:

Candle Burning

Physical change is melting of wax:

The chemical change is the burning of gas with the evolution of CO₂

Digestion of Food

Physical change is the breakdown of larger food molecules to simpler ones

The chemical change is the digestion of food by the action of HCl and enzymes.

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

Solution:

The setting of curd is a chemical change because curd cannot be turned back to milk. The properties of milk and curd are different.

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

Solution:

Cutting of wood is a physical change as it does not change the nature of the wood. On the other hand, burning of wood is a chemical change as wood is converted to charcoal with the liberation of CO_2.

8. Describe how crystals of copper sulphate are prepared.

Solution:

Crystals of copper sulphate are prepared using the crystallization method, which is described as follows

• Take a cupful of water in a beaker.
• Add a few drops of dilute sulphuric acid to this.
• Heat the water and when it starts boiling, add copper sulphate powder while still stirring.
• Add the copper sulphate powder till the solution becomes saturated. Filter into a china dish and allow it to cool.
• The solution should be kept undisturbed. Slowly, the crystals of copper sulphate separate out.

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

Solution:

Rusting of iron requires contact with water (moisture) and oxygen. By painting an iron gate, we prevent the contact between iron, Oxygen and water (moisture), this helps in preventing rusting of iron.

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

Solution:

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

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

Solution:

The answer is (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

Solution:

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

Important topics covered in NCERT Solutions for Class 7 Science Chapter 6 Physical and Chemical Changes

1. Physical Changes
2. Chemical Changes
3. Rusting of Iron
4. Crystallisation

Class 7 Science NCERT Solutions – Physical and Chemical Changes

We all see different types of changes in our daily life activities, among which a few are reversible and few are irreversible. Some examples of these changes include-melting of ice, a bud changing to a flower, melting of a candle wax and a lot more. Based on their changes, they are classified into physical change and chemical change.

Physical change: A change that changes only the physical traits of the substance, without making any change in their internal structure. Examples of physical change include: boiling of water, chopping wood, dissolving sugar in water, crumpling of paper, melting an ice cube, etc.

Chemical change: A change that changes by affecting the internal structure of the substance to form a new substance. Examples of chemical change include: digesting food, burning wood, baking a cake, curdling of milk, mixing acid, boiling an egg, rusting of iron, etc.

We, at CoolGyan’S, provide NCERT Solutions for Class 7 Science in a chapter-wise format to help students in their studies. All the solutions in this study material are explained in a simple language and in an easy methodology for students to learn better and effectively. These NCERT Solutions for Class 7 Science – Chapter 6, Physical and Chemical Changes provide complete information regarding the topic along with the definitions and examples. These NCERT Solutions are available in pdf format and students can directly download these materials or can practise online, by visiting our website at CoolGyan’S.