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

Multiple Choice Questions

1. Which of the following is a physical change? 

(a) Rusting of iron 

(b) Combustion of magnesium ribbon 

(c) Burning of candle 

(d) Melting of wax

Ans: (d) Melting of wax

Explanation:  A physical change occurs when the physical form of a substance changes but not its chemical content. In most cases, physical alterations can be reversed. Only the conversion of ice into water is an example of a physical change that can be reversed when we look at the possibilities provided.

2. Which of the following is a chemical change? 

(a) Twinkling of stars

(b) Cooking of vegetables 

(c) Cutting of fruits 

(d) Boiling of water

Ans: (b) Cooking of vegetables 

Explanation: A chemical reaction produces a chemical change. When matter changes shapes but not chemical identity, this is referred to as physical transformation. A physical alteration simply impacts physical properties, such as shape, size, and so on. If the chemical makeup changes, it is a chemical change; if the chemical composition remains constant, it is a physical change. Physical changes include the twinkling of stars, the chopping of fruits, and the boiling of water.

3. A chemical change may involve – 

(a) Change in colour only 

(b) Change in temperature only 

(c) Evolution of gas only 

(d) Any or all of the above

Ans: (d) Any or all of the above

Explanation: The chemical change could result in a change in colour, temperature, or the evolution of a gas, among other things.

4. Which of the following is/are true when milk changes into curd? 

(i) Its state is changed from liquid to semi solid. 

(ii) It changes colour. 

(iii) It changes taste. 

(iv) The change cannot be reversed. 

Choose the correct option from below : 

(a) (i) and (ii) are correct 

(b) (ii) and (iii) are correct 

(c) (i), (iii) and (iv) are correct 

(d) (i) to (iv) are correct

Ans: (c) (i), (iii) and (iv) are correct 

Explanation: The physical state of curd differs from that of milk. The taste of milk and curd is also distinct. The chemical reaction that converts milk to curd is irreversible.

5. A man painted his main gate made up of iron, to 

(i) Prevent it from rusting. 

(ii) Protect it from the sun. 

(iii) Make it look beautiful. 

(iv) Make it dust free. 

Which of the above statement(s) is/are correct? 

(a) (i) and (ii)

(b) (ii) and (iii) 

(c) only (ii) 

(d) (i) and (iii)

Ans: (d) (i) and (iii)

Explanation: It is vital to paint iron to keep it from rusting and to make it seem nice.

6. Iron pillar near the Qutub Minar in Delhi is famous for the following facts. Which of these facts is responsible for its long stability? 

(a) It is more than 7 metres high. 

(b) It weighs about 6000 kg. 

(c) It was built more than 1600 years ago. 

(d) It has not rusted after such a long period

Ans: (d) It has not rusted after such a long period

Explanation: The 'iron pillar' is notable for not rusting after such a long time.

7. Galvanisation is a process used to prevent the rusting of which of the following? 

(a) Iron 

(b) Zinc 

(c) Aluminium 

(d) Copper

Ans: (a) Iron 

Explanation: 'Galvanisation' is a process used to keep 'iron' from rusting. In this technique, we put a layer of 'zinc' to the surface of the iron.

8. Paheli’s mother made a concentrated sugar syrup by dissolving sugar in hot water. On cooling, crystals of sugar got separated. This indicates a – 

(a) Physical change that can be reversed.

(b) Chemical change that can be reversed. 

(c) Physical change that cannot be reversed. 

(d) Chemical change that cannot be reversed.

Ans: (a) physical change that can be reversed.

Explanation: The presented circumstance denotes physical change that is reversible.

9.  Which of the following statements is incorrect for a chemical reaction? 

(a) Heat may be given out but never absorbed. 

(b) Sound may be produced. 

(c) A colour change may take place. 

(d) A gas may be evolved.

Ans: (a) Heat may be given out but never absorbed. 

Explanation: Depending on the nature of the reaction, heat can be given or absorbed in a chemical reaction.

10. Two drops of dilute sulphuric acid were added to 1 g of copper sulphate powder and then a small amount of hot water was  added to dissolve it (step I). On cooling, beautiful blue coloured crystals got separated (step II). Step I and step II are: 

(a) Physical and chemical changes respectively. 

(b) Chemical and physical changes respectively. 

(c) Both physical changes. 

(d) Both chemicals change.

Ans: (c) Both physical changes. 

Explanation: A chemical change occurs when 'copper sulphate powder' dissolves in water in the presence of 'sulphuric acid.' While cooling the obtained hot solution, the crystals of 'copper sulphate' will separate.

Very Short Answer Questions

11. State whether the following statements are true or false: 

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

(b) Anaerobic bacteria digest animal waste and produce biogas. 

(c) Ships suffer a lot of damage though they are painted. 

(d) Stretching of rubber band is not a physical change. 

Ans: 

(a) The given statement is true. 

(b) The given statement is true. 

(c) The given statement is true. 

(d) The given statement is false. Stretching of a rubber band is a ‘physical change’. 

12. Melting of wax is a change where a solid changes to liquid state. Give one more such change which you observe in your surroundings. 

Ans: When a candle is lit, two things happen at the same time. The first step is to melt the wax, and the second step is to burn the wax. In these cases, melting wax is a physical change, whereas burning wax is a chemical reaction. Because burning causes oxidation of wax, which is a chemical change. Another example, according to the provided criteria, is 'Melting of ice.'

13. What kind of change is shown by tearing of paper?

Ans: Paper tearing is a physical change that cannot be undone.

Short Answer Questions

14. Match the items of Column I with the items of Column II.

Ans: The arranged table is given below: 

15. Fill in the blanks in the following statements using the words given in the box.

rusted, colourful, substance, chemical, physical, reversible, iron oxide, object

(a) Making sugar solution is a ____________ change. 

Ans: Making sugar solution is a physical change. 

(b) A physical change is generally____________. 

Ans: A physical change is generally reversible. 

(c) Grinding of wheat grain changes its size. It is a ____________ change. 

Ans: Grinding wheat grain changes its size. It is a  physical change.

(d) Iron benches kept in lawns and gardens get____________. It is a _________ change because a new _________ is formed.

Ans: Iron benches kept in lawns and gardens get rusted. It is a chemical change because a new substance is formed.

16. Classify the following processes into physical or chemical changes: 

(i) Beating of aluminium metal to make aluminium foil. 

(ii) Digestion of food. 

(iii) Cutting of a log of wood into pieces. 

(iv) Burning of crackers.

Ans: 

(i) Beating of aluminium metal to make aluminium foil: Physical change.

(ii) Digestion of food: Chemical change

(iii) Cutting of a log of wood into pieces: Physical change

(iv) Burning of crackers: Chemical change

17. Write word equations for two chemical reactions with the help of materials given in the box. 

Air, copper sulphate, iron, vinegar, iron oxide, carbon dioxide, iron sulphate, copper, lime water, water

Ans: The reactions are given below: 

$Iron\; + \;Air\; + \;water\; \to \;Iron\;oxide$  and

$Copper\;sulphate\; + \;Iron \to \;Iron\;sulphate\; + \;copper\;$

18. Explain the following: 

(a) Lime water turns milky on passing carbon dioxide gas into it.

Ans: When carbon dioxide gas is introduced into lime water, a white precipitate of 'calcium carbonate’ is formed. This comment elicited the following response:

Calcium hydroxide + Carbon dioxide → Calcium carbonate + water 

(b) Bubbles are produced when acetic acid is added to a solution of sodium hydrogen carbonate.

Ans: The chemical interaction between 'acetic acid' and' sodium hydrogen carbonate' produces 'carbon dioxide.' This comment elicited the following response:

Sodium hydrogen carbonate + Acetic acid→ Sodium carbonate + water + Carbon dioxide

Long Answer Questions

19. Give two examples for each of the following cases: 

(a) Physical changes which are reversible. 

Ans: Physical changes which are reversible: 

i) Melting of ice.

ii) Folding of clothes.

(b) Physical changes which are not reversible. 

Ans: Physical changes which are not reversible: 

i) Breaking a bottle. 

ii) Cutting of trees. 

(c) Chemical changes.

Ans: Chemical changes: 

i) Burning wood. 

ii) Digesting food

20. Give an example of a chemical reaction for each of the following situations: 

(a) A change in colour is observed.

Ans: The chemical reaction between 'copper sulphate' solution and iron metal results in a colour shift. Because of the creation of iron sulphate, the blue colour of 'copper sulphate' changes to vivid green in this chemical reaction. The response is,

$\mathop {Copper\;sulphate}\limits_{\left( {blue} \right)}  + \mathop {Iron}\limits_{\left( {grey} \right)}  \to \;\mathop {Iron\;sulphate}\limits_{\left( {bright/light\;green} \right)} \; + \;\mathop {Copper}\limits_{\left( {brown} \right)} $

(b) A gas has evolved. 

Ans: When 'baking soda' and 'vinegar' are mixed, a chemical reaction occurs. Following this, bubbles of 'carbon dioxide' gas, combined with another material, are generated. The response is,

$\mathop {Baking\;soda}\limits_{\left( {Sodium\;hydrogen\;carbonate} \right)}  + \mathop {Vinegar}\limits_{\left( {acetic\;acid} \right)}  \to Sodium\;acetate\; + \;Carbon\;dioxide\; + \;water\;\;\;$

(c) Sound is produced. 

Ans: Burning crackers also generate a loud sound.

21. If you leave a piece of iron in the open for a few days, it acquires a film of brownish substance, called rust. 

(a) Do you think rust is different from iron? 

Ans: Rust is brown dust made up of 'iron oxide.' Rust, on the other hand, is not the same as iron.

(b) Can you change rust back into iron by some simple method? 

Ans: No, rusting is a chemical reaction that is irreversible.

(c) Do you think the formation of rust from iron is a chemical change? 

Ans: In the presence of moisture, iron rusts and combines with oxygen. This results in the formation of a new chemical known as 'iron oxide.' Rust is another name for iron oxide.

(d) Give two other examples of a similar type of change. 

Ans: The following are two examples:

(i) Production of 'magnesium oxide' by burning' magnesium ribbon'.

(ii) The formation of curd from milk.

22. A student took a solution of copper sulphate in a beaker and put a clean iron nail into it and left it for about an hour. 

(a) What changes do you expect? 

Ans: The following are the expected changes based on the supplied statement:

(i) The colour changes from blue to green.

(ii) A brown colour deposit is discovered on an iron nail (surface).

(b) Are these changes chemical in nature? 

Ans: Yes, these alterations are chemical in nature. The reason for this is that the reaction produces 'iron sulphate' and copper.

(c) Write a word equation for the chemical change, if any.

Ans: The reaction is: 

$\mathop {Copper\;sulphate}\limits_{\left( {Blue} \right)}  + \;\mathop {Iron}\limits_{\left( {Shining\;white} \right)}  \to \;\mathop {Iron\;sulphate}\limits_{\left( {Green} \right)}  + \;\mathop {Copper}\limits_{\left( {Brown} \right)} $

$\underset{\left( Blue \right)}{\mathop{Copper~sulphate}}\,~+~\underset{\left( Shining~white \right)}{\mathop{Iron}}\,~\to ~\underset{\left( Green \right)}{\mathop{Iron~sulphate}}\,~+~\underset{\left( Brown \right)}{\mathop{Copper}}\,~$ 

Benefits of solving the Exemplar of Class 7, Chapter 6

The solution for the Exemplar of Class 7, Chapter 6, Physical and chemical changes help the students in the following manner: -

• It gives students extra practice helpful for understating the chapter in a detailed manner.

• It prepares the students mentally to solve any type of questions in the exam.

• It serves as a measuring tool for the students to measure their progress.

Therefore, Vedantu provides the solutions for the Exemplar of Class 7, Chapter 6.

Also, if you are looking for the solutions of the Exemplar for the previous chapter, which is, Acids, Bases and Salts you can find it here: NCERT Exemplar Class 7 Science Solutions Chapter 5 Acids, Bases and Salts (vedantu.com)