Important Questions Class 7 Science Chapter 6

Important Questions Class 7 Science Chapter 6 – Physical and Chemical Changes

Class 7 Science Chapter 6 is one of the most important chapters, which teaches about the Physical and Chemical Changes of the substances we find around us. We all experience different types of changes related to our daily life activities. Some of these activities are reversible, and few are irreversible. For example, setting curd from milk, melting ice, melting candle wax, rusting iron, etc. Based on the nature of their changes, they are broadly classified into physical and chemical changes.

A physical change is a change in a substance’s physical properties( shape, size, colour, and state). No new substance is formed in such a change and it is generally reversible. A chemical change always gives one or more new substances. A chemical change is also referred to as a chemical reaction. The other important concepts covered in Class 7 Science Chapter 6 are iron rusting, crystallisation, and galvanisation.

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Class 7 Science Chapter 6 is one of the most important chapters, which teaches about the Physical and Chemical Changes of the substances we find around us. We all experience different types of changes related to our daily life activities. Some of these activities are reversible, and few are irreversible. For example, setting curd from milk, melting ice, melting candle wax, rusting iron, etc. Based on the nature of their changes, they are broadly classified into physical and chemical changes.

Our Important Questions for Class 7 Science Chapter 6 question bank is a comprehensive set of questions compiled from various sources, including the NCERT textbook, NCERT exemplar books, and so on, to assist students in thoroughly revising the topics and performing well in the examination.Our expert faculty members have prepared step-by-step instruction-based answers for all questions. So students can easily revise the chapters while going through these sets of important questions.

Important Questions Class 7 Science Chapter 6 – With Solutions

The questions from our question bank of Chapter 6 Class 7 Science Important Questions are very helpful for students preparing for CBSE examinations. The Extramarks team understands the importance of students revising the chapter by solving questions. Hence, our team of expert Science teachers have prepared a comprehensive list of Science Class 7 Chapter 6 Important Questions with detailed solutions, including textbook exercise questions and answers, MCQs, short answer questions, and long answer questions taken from the NCERT textbook, NCERT exemplars, etc. Students are advised to solve questions from our question bank while revising the chapter to clear all their doubts.

Students can get access to the solutions for all the Important Questions Class 7 Science Chapter 6 once they register on our website.

Below is a sample list of a few questions and their solutions from our question set of Class 7 Science Chapter 6 Important Questions.

Question 1. Which of the following is/are right when milk changes into

curd?

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

(b) It changes colour.

(c) It changes the taste.

(d) Cannot reverse the change.

Choose the correct option from below :

(i) (a) and (b) are correct

(ii) (b) and (c) are correct

(iii) (a), ©, and (d) are correct

(iv) (a) to (d) are correct

Answer 1. Option (iii) (a), (c) and (d) are correct

Explanation: Option (iii) is correct; When a little curd is added to milk, the milk, which is in the liquid state, takes the form of a semi-solid substance called “curd”, with different chemical compositions and properties. Because it is a chemical reaction, this curd cannot be converted back into milk; thus, the change is permanent and irreversible. The taste of the curd is sour and does not change colour.

Question 2. Fill in the blanks :

(a) The chemical name of baking soda is _________.

(b) When carbon dioxide is passed through lime water, it turns milky due to the formation of _________.

(c) Changes in which only _________ properties of a substance change are called physical changes.

(d) Two methods which can prevent rusting of iron are _________ and _________.

(e) Changes in which new substances are formed are called _________ changes.

Answer 2. 

1. Sodium hydrogen carbonate
2. Calcium carbonate.
3. Physical
4. Galvanisation and painting
5. Chemical

Question 3. If you leave a piece of iron in the open for a few days, it acquires a film of a brownish substance called rust.

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

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

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

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

Answer 3. 

1. Rust is different from iron. Rust is a brownish substance called iron oxide, formed on iron due to the chemical reaction of iron, water and atmospheric oxygen.
2.  No, changing rust back into iron is not possible.
3. Yes, the formation of rust from iron is a chemical change and cannot be reversed.
4. Burning of paper and ripening of fruits.

Question 4. Classify 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 4.

(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 5. Write the colour of the copper sulphate solution obtained when iron nails are dipped in it.

Answer 5. The colour of the sulphate solution is changed to green when iron nails are dipped in it.

Question 6. Mention two examples for each of the following cases:

(a) Reversible Physical changes.

(b) Physical changes which are not reversible.

(c) Chemical changes.

Answer 6. 

(a) Reversible Physical changes – Melting of wax, freezing of ice.

(b) Physical changes which are not reversible- Breaking of glass, chopping of vegetables

(c) Chemical changes- Burning wood, Cooking an egg.

Question 7. The kitchen gas we use is liquified petroleum gas (LPG). In the cylinder, it is in a liquid state. When it comes out of the cylinder, it becomes a gas (Change – A) and then burns (Change – B). The following statements pertain to these changes. Choose the correct one.

(a) Procedure– A is a chemical change.

(b) Procedure– B is a chemical change.

(c) Both procedures A and B are chemical changes.

(d) None of these procedures is a chemical change.

Answer 7. Option (b) Action– B is a chemical change is a correct answer.

Explanation:

In change – A, the gas only changes its physical state from liquid to gas, and no new substance is formed in this procedure. This is not a chemical change and hence is not the correct option.

In Change – B, the gas burns to produce heat and carbon dioxide. This reaction is not reversible; it is a chemical change.

Question 8. Write the correct equations for two chemical reactions with the help of the items given below.

Air, copper sulphate, iron, iron oxide, carbon dioxide, iron sulphate, copper, water, silver

Answer 8:

(a) Copper sulphate + iron → iron sulphate + copper

(b) Iron + air + water → iron oxide

Question 9. Anaerobic bacteria assimilate animal waste and produce Biogas (Change – A). The Biogas is later burnt as fuel (Change – B). The following statements pertain to these changes. Choose the correct one.

(a) Activity – A is a chemical change.

(b) Activity – B is a chemical change.

(c) Both activities A and B are chemical changes.

(d) None of these activities are a chemical change.

Answer 9. (c) Both activities A and B are chemical changes.

Explanation: 

Activity A illustrates a chemical reaction where the animal waste undergoes decomposition by anaerobic bacteria and changes the chemical composition of the components to produce biogas.

anaerobic bacteria

Animal waste ——————————-> Biogas (fuel)

decomposition

Further, in activity B, the Biogas is burnt to produce an irreversible new substance.

Heat

Biogas(fuel) ——————> Energy + Ash

From the above, we can conclude that activities A and B are chemical changes.

Question 10. Give one example of a chemical reaction for each of the following :

(a) A colour change is observed.

(b) A gas has evolved.

(c) Sound is produced.

Answer 10. 

(a) A change in colour is observed: Chemical reaction between Copper sulphate solution (blue) and Iron is

Copper sulphate solution + Iron ⟶ Iron sulphate + Copper

In the above reaction, a copper sulphate solution(blue colour) reacts with an iron substance, for example, an iron nail(grey colour) and produces new chemical substances, iron sulphate solution( light green colour) and copper (brown colour) formed on the iron nail.

(b) A gas is evolved: the chemical reaction between baking soda and vinegar

Baking soda + vinegar ⟶ sodium acetate + carbon dioxide(gas) + water

The baking soda and vinegar mixture give rise to carbon dioxide gas and two other substances.

(c)  Sound is produced: Firework explosion.

Explosions of fireworks produce sound, heat, light, and gases.

Question 11. Match the items of Column I with the items of Column II.

Answer 11. The matched items are shown below

Question 12. Fill in the blanks using the words mentioned below.

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

(a) Making sugar solution is a ____________ change.

(b) A physical change is generally____________.

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

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

Answer 12. 

1. Physical
2. Reversible
3. Physical
4. Rusted, chemical, object

Question 13. Mention as true or false for the following statements. If a statement is false, write the correct statement.

(a) Manure produced from leaves is a physical change. 

(b) Cutting a wood log into pieces is a chemical change. 

(c) Zinc-coated iron pipes do not get rusted easily. 

(d) Rust and iron are the same substances. 

(e) Steam condensation is not a chemical change. 

Answer 13. 

1. False. The manure formed from leaves is a chemical change. Fungi and bacteria decompose the dead leaves to form manure, which is  used as a fertiliser for agriculture.
2. False. Cutting a wood log into pieces is not a chemical change, as no new substance is formed. It is a physical change, as only wood’s physical properties(shape and size) are changed.
3.  True.
4.  False. Iron is a metal, whereas rust is brown-coloured dust formed on iron due to chemical reactions.
5. True

Question 14. The iron pillar close to the Qutub Minar tower in Delhi is famous for the below-mentioned facts.

(a) It weighs about 6000 kg.

(b) It is more than 7 metres high.

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

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

Answer 14. (d) It has not rusted after such a long period.

Explanation: The Qutub Minar does not contain sulphur/magnesium in it. Hence, there is no chemical reaction with air to form rust on the iron.

Question 15. From the below statements, mention the incorrect statement for a chemical reaction.

(a) Sound may be produced.

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

(c) A gas may be evolved.

(d) A colour change may take place.

Answer 15. (b) Heat may be given out but never absorbed.

Explanation: During a chemical reaction, heat may be given out or absorbed

Question 16. When the candle burns, both physical and chemical changes occur. Point out these changes. Mention another example of a familiar process in which chemical and physical changes occur.

Answer 16. The physical and chemical changes of the candle when it burns are explained below.

Physical change: when a candle burns, the wax melts down to form a liquid state, and upon cooling, the melted wax solidifies. The physical property (shape) of the candle is changed.

Chemical change: Burning a candle releases heat, light(vapours), and carbon dioxide, a chemical reaction.

Another example involving both physical and chemical changes is,

Digestion of food :

Physical change: The large food particles are broken down into smaller particles to absorb nutrients.

Chemical change: The complex molecules of proteins, fats, and carbohydrates are processed into smaller molecules that can be absorbed by the cells through chemical digestion called hydrolysis using water and digestive enzymes.Benefits of Solving Important Questions Class 7 Science Chapter 6

To be well prepared for the examinations, students should have a deep understanding of all the topics included in the curriculum. One of the suggested ways to revise the topics is by practising many of the questions from the chapter.

Students can rely on our question bank and its solutions for this. By referring to and practising from our Important Questions Class 7 Science Chapter 6, students will get a complete understanding of all the complex concepts and get familiarised with the exam question patterns.

Let us explore some benefits of studying from our question bank of Important Questions Class 7 Science Chapter 6:

• The question bank of important questions consists of various types of questions, including MCQs, short and medium-format-questions and answers, CBSE extra questions, and long answer questions, which our experienced science professors carefully prepare as per the CBSE syllabus and NCERT guidelines and by referring to various trusted sources, including NCERT textbooks, NCERT exemplar books, past years’ question papers and other sources.
• The chapter-wise questions and detailed solutions provided by Extramarks help students be confident in the concepts and prepare well for examinations. By rigorously practising these advanced level questions from the Important Questions Class 7 Science Chapter 6, students can thoroughly brush up on the concepts, analyse their shortcomings, and overcome them before facing their final examinations.
• All the Important Questions Class 7 Science Chapter 6 has detailed solutions to all the questions in the textbook. Also, the tricky questions between chapters make students think laterally and apply the concepts learned in the chapter. Multiple choice questions have a significant weightage in board examinations and require a lot of critical thinking to solve. Extramarks provides the complete list of chapter-wise multiple-choice questions to help students prepare effectively for examinations.
• By solving CBSE sample papers, you can not only have a clear idea of the question paper pattern, but you will also be able to track your weak and strong areas and work on improving them. You will also be able to improve your time management skills.

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