NCERT Class 6 Science Chapter 6 Changes Around Us

NCERT Class 6 Science Chapter 6 Changes Around Us Solutions to each chapter is provided in the list so that you can easily browse through different chapters NCERT Class 6 Science Chapter 6 Changes Around Us and select need one. NCERT Class 6 Science Chapter 6 Changes Around Us Question Answers Download PDF. NCERT Class 6 Science Solutions.

NCERT Class 6 Science Chapter 6 Changes Around Us

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Also, you can read the NCERT book online in these sections Solutions by Expert Teachers as per Central Board of Secondary Education (CBSE) Book guidelines. CBSE Class 6 Science Solutions are part of All Subject Solutions. Here we have given NCERT Class 6 Science Chapter 6 Changes Around Us and Textbook for All Chapters, You can practice these here.

Separation of Substances

Chapter: 6

NCERT TEXT BOOK EXERCISES

Q.1. To walk through a waterlogged area, you usually shorten the length of your by folding it. Can this change be reversed?

Ans: Yes, this change can be reversed.

Q. 2. You accidently dropped your Favorite toy and broke This is a change, you did not want. Can this change reversed? 

Ans: No, this change cannot be reversed.

Q.3. Something are listed in the following table. For each change write in blank column whether the change can be reversed or not.

Ans: 

Q. 4. A drawing sheet changes when you draw a picture on it. Can you reverse this change?

Ans: No, we cannot reverse this change. 

Q. 5. Give examples to explain the difference between changes that can or cannot be reversed.

Ans: A change that can be reversed is called a reversed change. For example, blowing of a balloon, making aeroplane from a of paper by folding it and making ball from a dough etc., changes can be reversed.

A change that cannot be reversed is called irreversible change.

For example: Ripening of fruits, burning paper and cooking of food, etc., cannot of be reversed.

Q. 6. A thick coating of a paste of plaster of paris (POP) is applied over the bandage on a fractured bone. It becomes hard on drying to keep the fractured bone immobilized. Can the change in POP be reversed?

Ans: No, the change cannot be reversed. 

Q. 7. A bag of cement lying in the open gets wet due to rain during the night. The next day the sunshine brightly. Do you think the changes, which have occurred in the cement could be reversed?

Ans: No, the change cannot be reversed.

SOME OTHER IMPORTANT QUESTIONS FOR EXAMINATION

VERY SHORT ANSWER QUESTIONS

Q. 1. “Ice melts to form water”. What is the cause of this change?

Ans: Heat.

Q. 2. Ice can be changed into water and water can be changed back into ice. What is the general name of such changes?

Ans: Reversible changes.

Q. 3. Milk can be changed into curd but curd cannot be changed back into milk. What is the general name of such changes?

Ans: Irreversible changes.

Q. 4. State whether burning of paper is a reversible change or an irreversible change.

Ans: Irreversible change. 

Q. 5. Can you get back the match stick from the ash left over by a burning match stick?

Ans: We cannot get back the match stick from the ash left over by a burning match stick.

Q. 6. Write two changes happening in our body. 

Ans: (i) Our nails grow. 

(ii) We Growtaller.

Q. 7. Why melting of wax is a reversible change?

Ans: Melting of wax is a reversible change because solid wax melts on heating and melting wax becomes solid on cooling.

Q. 8. What is a physical change?

Ans: A change in which no new substance is formed is called a physical change. 

Q. 9. What is a chemical change?

Ans: A change in which a new substance is formed is called a chemical change.

Q. 10. State whether glowing of an electric bulb is a reversible change or an irreversible change.

Ans: Reversible change.

Q. 11. Why growth of plants is an irreversible change?

Ans: A tree cannot be reversed back into a plant or seed. Therefore, growth of a plant is an irreversible change.

Q. 12. Give one use of the expansion of an object on heating.

Ans: Fixing of iron rim to the wooden wheel of a cart.

Q. 13. Give an example to show that force changes the shape of a material.

Ans: When a spring is pulled, its shape and size change.

Q. 14. Give an example to show that pressure changes the shape of material.

Ans: When an inflated balloon is pressed between two hands, its shape and size change.

Q. 15. Which property of moulding clay can be changed on heating?

Ans: It becomes hard.

SHORT ANSWER QUESTIONS

Q. 1. Formation of clouds is a physical change. Explain.

Ans: Clouds are formed by condensation of water vapors present in the atmosphere. When rain water gets back on the earth, no new product is formed. Therefore, it is a physical change.

Q. 2. Distinguish between reversible and irreversible changes.

Ans: 

Q. 3. A metal bar when heated, expands. What type of a change is there? Why?

Ans: The expansion of metal bar on heating is a reversible change. The metal bar is changed into its original size when it is cooled. Thus the change occurred, is not of permanent nature and thus it is a reversible change.

Q. 4. An iron rim is made slightly smaller than the wooden wheel around which it is to be fitted. This iron rim is heated uniformly due to which it under- goes a change P and can be easily put around the wooden wheel. When cold water is poured over this hot iron rim, it undergoes change Q and fits tightly over the wheel. After a considerable time, a change R takes place in the iron rim due to which a red-brown coating is formed on it. 

(a) What are the changes (i) P. (i) Q and (i) R?

Ans: (i) Expansion.

(ii) Contraction.

(iii) Rusting.

(b) Out of P. Q and R, which change/ changes is/are reversible?

Ans: P and Q are reversible changes.

Q. 5. Name the cause of change which takes place during the:

(a) Conversion of ice into water. 

Ans: Heat.

(b) Conversion of water into hydrogen and oxygen.

Ans: Electricity.

(c) Formation of image of a person on a photographic film 

Ans: Light.

(d) Bending of iron rods to make an iron grille.

Ans: Force.

Q. 6. between a physical change and chemical change.

Ans:

Q. 7. Write two characteristics of physical changes.

Ans: (i) A physical change affects only the physical properties such as size, shape and state of a substance.

(ii) No new substance is formed during a physical change. 

Q.8. Classify the following into physical and chemical changes. 

(a) Melting of wax. 

(b) Burning of agarbatti. 

(c) Tearing of cloth. 

(d) Cooking of food. 

Ans: (a) Melting of wax ___________ physical change.

(b) Burning of agarbatti __________chemical change.

(c) of cloth ____________ physical change.

(d) Cooking of food ___________ chemical change.

Q.9. What is the difference between the following changes?

(a) Rolling of roti from dough. 

Ans: Rolling of roti from dough is a reversible change. We can convert the rolled roti back into the dough.

(b) Baking of roti.

Ans: Backing of roti is an irreversible change because baked roti cannot be changed back into the original dough.

Q.10. How do the following changes differ from one another?

(a) Melting of wax.

Ans: Melting of wax is a reversible change because solid wax melts on heating and melted wax becomes solid on cooling.

(b) Burning of war. 

Ans: Burning of wax is an irreversible change. we light the candle then the wax present in it starts burning to produce heat and light. The burning of wax also produces carbon dioxide gas, water vapour and soot which all go into the air. We cannot combine all the of burning of wax to get back the original candle.

Q. 11 Why the dissolution of common salt in water is a physical change?

Ans: Dissolution of common salt in water is a physical change on account of the following reasons:

(i) There is no change in the composition of common salt.

(ii) The change is temporary and easily reversible.

SHORT ANSWER QUESTIONS

Q. 1. Explain how a metal rim slightly smaller than a wooden wheel can be fixed on it.

Ans: The metal rim is always made slightly smaller than the wooden wheel. The metal rim is heated. On heating, the rim expands and fits on to the wheel. Cold water is then poured over the rim. Due to cooling the metal rim contracts and fits tightly on to the wheel.

Q. 2. A white powdery substance X immediately sets into a hard mass on adding a liquid Y to it. In hospitals, a thick coat of the paste of substance X is applied over the bandage on the fractured bone of a patient to keep up fractured bone in place to get joined properly. 

(a) What could the substance X be?

Ans: Plaster of Paris (POP).

(b) Name the liquid Y.

Ans: Water. 

(c) What type of change occurs in X on adding Y? 

Ans: Irreversible.

Q. 3. When a liquid X is added to a grey powdery substance Y, the substance Y slowly sets into a hard mass. A thick paste of substance Y and sand made in liquid X is used for plastering the walls of houses.

(a) What could the liquid X be?

Ans: Water.

(b) Name the substance Y. 

Ans: Cement.

(c) What type of change occurs on adding X to Y? 

Ans: Irreversible change.

Q. 4. Write three characteristics of a chemical change.

Ans: Characteristics of a chemical change:

(i) In a chemical change, the chemical composition and chemical properties of the heating substance are completely changed. 

(ii) Whenever a chemical change takes place, one or more, new substances are formed. 

(iii) A chemical change cannot be reversed easily.

Q. 5. Define a physical and a chemical change. Give an example of each.

Ans: Physical change: A change in which only the physical properties of a substance get changed and no new substance is formed is called a physical change.

Example: Dissolution of sugar in water. 

Chemical change: An irreversible change in which the composition and chemical properties of the reacting substances get changed and which cannot be reversed by reversing the conditions, is called a chemical change.

Example: Burning of coal/wood 

Q. 6. Heat is necessary for some chemical changes to take place. Explain with an example.

Ans: When iron and sulphur are mixed, they do not react. On heating a mixture of iron and sulphur in a test tube, a black substance of iron sulphide is formed. The iron in iron sulphide cannot be separated physically with a magnet. This indicates that an irreversible change has taken place because of heating. Hence heat is necessary for some chemical changes to take place

Q.7. Classify the following as chemical or physical changes, giving reasons. 

(a) Melting of butter in a pan.

Ans: Melting of butter in a pan is a physical change since there is no change in the chemical composition of butter, only the physical state changes from solid to liquid.

(b) Passing of electric current through water and water breaking down into hydrogen and oxygen gases and 

Ans: Passing of electric current through water to form hydrogen and oxygen is a chemical change, since the properties of. hydrogen (combustible gas) and oxygen (supporter of combustion) are altogether different from those of water which is neither combustible nor a supporter of combustion but it actually extinguishes fire.

(c) Making a fruit salad with raw fruits.

Ans: Making a fruit salad with raw fruits is a physical change since there is no change in the chemical properties of the fruits but only the physical appearance has changed.

Q. 8. Identify the physical and chemical changes from the following giving reasons:

(i) Tarnishing of silver.

Ans: Silver combines with hydrogen sulphide gas present in the air to form silver sulphide which tarnishes the silver. Since silver sulphide is a new compound having properties different from those of silver and hydrogen sulphide gas. Tarnishing of silver is a chemical change.

(ii) Ripening of fruits.

Ans:  During ripening of fruits, chemical changes occur, due to which sourness decreases and sweetness increases. Therefore, ripening of fruits is a chemical change.

(iii) Dissolution of sulphur in carbon.

Ans: Dissolution of sulphur in carbon disulphide is a physical change because sulphur can be obtained by evaporating carbon disulphide.

Q. 9. Can physical and chemical. changes occur together? Illustrate your answer.

Ans: In some cases, physical and chemical changes occur together. One such example is burning of candle. The solid wax in the candle first changes into liquid state and then into the vapour state. Both these changes are physical changes. The wax vapours then combine with oxygen of the air to form a mixture of carbon dioxide and water. This involves a chemical change. The unburnt wax vapours again change first to the liquid state and finally to the solid state. interconversion of states is a physical change. Thus, burning of candle involves both physical and chemical changes.

Q. 10. Identify the type of change and state whether energy is evolved or absorbed in each one of the following:

Burning of a candle, lighting of a bulb, preparation of food by green plants

Ans: (i) Burning of a candle: Chemical change, energy evolved.

(i) Lighting of a bulb: Physical change, energy evolved.

(iii) Preparation of food by green plants: Chemical change, energy absorbed.

LONG ANSWER QUESTIONS 

Q. 1. When is a change said to have taken place in a material? Explain with the help of an example.

Ans: We have many things around us.All these things have certain properties such as state (solid, liquid or gas), position, shape, size, colour, temperature, composition and structure, etc. When one or more properties of a thing become different, we say that it has changed or a change has taken place. Changes involve different kinds of alternations in the things around us. When a change takes place, there may be a change in the state, position, shape, size, colour, temperature, composition or structure of the material of the object.

When ice melts, it forms water. Ice is a solid, whereas water is a liquid. So, the melting of ice involves a change in state (form solid to liquid state). 

Q. 2. What is meant by reversible changes and irreversible changes? Explain with examples. 

Ans: Reversible change: A change which can be reversed to form the original substance is called a reversible change. 

Example: When we heat ice, it melts to form liquid water. A change from solid to liquid takes place during the melting of ice. Now, if we cool the water by keeping in the freezer of a refrigerator, it again changes into solid ice. the change from ice to water. by heating, has been reversed by cooling. Thus, the melting of ice to form water is reversible change.

Irreversible change: A change which cannot be reversed to from the original substance or substances is called irreversible change.

Example: If we burn a piece of paper, it changes into ash and smoke. Now, we cannot combine the ash and smoke to form the original piece of paper. So, the burning of paper is a change which cannot be reversed. Therefore, the burning of paper is an irreversible change.

Q. 3. Explain why, the burning of paper is said to be an irreversible change whereas the boiling of water is known as reversible change.

Ans: If we burn a piece of paper, it changes into ash and smoke. Now, we cannot combine the ash and smoke to form the original piece of paper. So, the burning of paper is a change which cannot be reversed. Hence, the burning of paper is an irreversible change. When we boil water by heating then it changes into steam. Now, if we cool the steam, then water is formed again. So, the changing of water into steam has been reversed by cooling. Thus, the boiling of water is a reversible change.

HIGHER ORDER THINKING SKILL QUESTIONS 

Q.1. Spot the location on a burning candle where

(a) A chemical change occurs.

(b) A physical change occurs.

Ans: 

Q. 2. When electricity is passed through water, then two gases, hydrogen and oxygen are produced. On the other hand, when heat is supplied to water, then another gas, steam is produced. What type of change takes place.

(a) In the first case? 

Ans: Irreversible change. 

(b) In the second case?

Ans: Reversible change.

Q.3. Why boiling of water to form steam is a reversible change? 

Ans: When we boil water by heating, then it changes into steam. Now, if we cool the steam, then is formed again. So, the changing of water into steam can be reversed by cooling. Thus, boiling of water to form steam is a reversible change.

Q. 4. Why is the burning a piece of paper is a chemical change?

Ans: When a piece of paper is burnt, some ash is left behind while carbon dioxide and water vapour are given out. The molecules of paper, ash, carbon dioxide and water are different from each other. Since new substances are formed, burning of paper is a chemical change.

Q. 5. Give reasons for the following:

(a) Ice cream melts when kept outside the refrigerator for a while.

Ans: Ice cream melts when kept outside the refrigerator for a while because it absorbs heat from the surroundings.

(b) Molten butter changes to solid when kept in the refrigerator due to cooling.

Ans: Molten butter changes to solid when kept in the refrigerator due to cooling.

(c) Balloon grows bigger in size when air is blown into it.

Ans: Balloon grows bigger in size when air is blown into it because the balloon gets inflated.

SKILL BASED QUESTIONS

Q.1. Write the change shown in this figure.

Ans: (a) The flour changes into dough (physical change).

(b) The dough changes into circular roti (physical change).

Q.2. Can this change be reversed?

Ans: Yes, on heating wax changes into liquid. On cooling, it again become solid. So, this change is Reversible.

FORMATIVE ASSESSMENT 

Q.1. Fill in the following blank with a suitable word:

(i) When one or more properties of a material become different, we say that a ________ has taken place in it.

Ans: Change.

(ii) Glowing of an electric bulb is a ________ change.

Ans: Physical.

(iii) Formation of steam from water is a ________ change.

Ans: Physical. 

(iv) Dissolution of carbon dioxide in water is a ________ change.

Ans: Physical. 

(v) Melting of wax is a ________ change.

Ans: Physical.

(vi) A change that cannot be reversed is called ________ change.

Ans: Irreversible.

(vii) Change in which one or more new substances are formed is called ________ change.

Ans: Chemical.

(viii) A change that can be reversed is called _________change.

Ans: Reversible.

(ix) A change in which no new substance is formed is called ________ change.

Ans: Physical.

(x) The composition of the substance remains unchanged during a ________ change. 

Ans: Physical. 

Q. 2. Match the items in column A with the items in column B:

Ans: 

Q.3. Give one word for the following:

(i) The change which can be reversed by reversing the conditions.

Ans: Reversible change.

(ii) The change which goes only in one direction.

Ans: Irreversible.

(iii) The change in which no new substance is formed.

Ans: Physical change.

(iv) The change in which the composition and chemical properties of the reacting substances get changed.

Ans: Chemical change.

(v) Conversion of a liquid into vapours.

Ans: Evaporation.

MULTIPLE CHOICE QUESTIONS

(i) Which one of the following is a reversible change?

(a) Water changing into ice.

(b) Nails becoming rusty.

(c) Bread turning moldy.

(d) Paper burning into ash.

Ans: (a) Water changing into ice.

(ii) When ice melts to form water, then a change occurs in its:

(a) Position.

(b) Temperature.

(c) State. 

(d) Composition.

Ans: (c) State.

(iii) Which one of the following is a beneficial change?

(a) Rusting of an iron object.

(b) Spoilage of food.

(c) Ripening of fruit.

(d) Souring of milk.

Ans: (c) Ripening of fruit.

(iv) When ice-cream melts: 

(A) Heat is lost from the ice Cream. 

(B) Heat is gained by the ice-cream.

(C) Heat is lost from an air.

(D) Heat is gained by the air.

(a) A B

(b) A and C  

(c) B and C

(d) B and D

Ans: (c) B and C.

(v) Which of the following is not reversible change?

(a) Boiling of water. 

(b) Boiling of an egg.

(c) Melting of wax.

(d) Boiling of alcohol.

Ans: (b) Boiling of an egg.

VALUE BASED QUESTIONS

Teacher fold in the class, all substances expand on heating and contract on cooling This property is used by blacksmiths to fix metal rims on wooden wheels. The metal rim is made slightly smaller than the wooden wheel and heated. The rim expands and becomes bigger in size. This hot metal rim is fixed on the wooden wheel and cold water is used to cool it. The metal rim contracts and holds the wooden wheel in a tight grip. 

Questions

(i) Name one application of expansion on heating and contraction on coding.

Ans: Fixing iron rim on the bullock-cart wheel.

(ii) How a metal rim slightly smaller than a usoden wheel can be fixed on it? 

Ans: The metal rim is always made slightly smaller than the wooden wheel. The metal rim is heated. On heating, the rim expands and fit onto the wheel Cold water is then poured over the rim. Due to cooling the metal rim contracts and fits tightly onto the wheel.

(iii) What value of teacher is reflected in the above act?

Ans: Teacher showed the value of helping, caring and responsible behaviour.