Changes Around Us | Science 6th | Chapter 6 | Questions and Answers

JANDKNCERT | Science 6^th |

Changes Around Us | Science 6th | Chapter 6 | Questions and Answers

 

Chapter 6: Changes Around Us

 

Introduction

In Chapter 5, we learnt about the Separation of Substances in which we learnt about the different methods used to separate impurities, non-useful components from the mixtures, such as, handpicking, threshing, winnowing, sieving, sedimentation, decantation, filtration, and evaporation. These methods of separation are helpful in our day to day activities. Solutions are saturated and unsaturated.

 

In this chapter, you will learn about the Changes Around Us. The following points will help you to understand this chapter easily.

•     Microbes are responsible for the decaying of organic matter.

•     Many changes are taking place around us on their own.

•     Some changes can be reversed and some cannot be reversed.

•     A change may occur by heating a substance or by mixing it with some other.

 

Let us try to answer some questions taken from the NCERT Book of Science Class 6th. This Exercise is taken from the same book.

 

Exercises

Q1. To walk through a waterlogged area, you usually shorten the length of your dress by folding it. Can this change be reversed?

 

Answer.

Yes, shorten the length of the dress by folding it, is a reversible change. We can unfold the length of the dress again.

 

Q2. You accidentally dropped your favourite toy and broke it. This is a change you did not want. Can this change be reversed?

 

Answer.

The broken toy can be fixed. This change can be reversed, in some cases, based on the material it is made of. Otherwise, this change cannot be reversed if the toy is completely broken.

 

Q3. Some changes are listed in the following table. For each change, write in the blank column, whether the change can be reversed or not.

 

S. No	Change	Can be reversed (Yes/No)
1.	The sawing of a piece of wood
2.	The melting of ice candy
3.	Dissolving sugar in water
4.	The cooking of food
5.	The ripening of mango/tomato
6.	Souring of milk

 

Answer.

 

S. No	Change	Can be reversed (Yes/No)
1.	The sawing of a piece of wood	No
2.	The melting of ice candy	Yes
3.	Dissolving sugar in water	Yes
4.	The cooking of food	No
5.	The ripening of mango/tomato	No
6.	Souring of milk	No

 

 

Q4. A drawing sheet changes when you draw a picture on it. Can you reverse this change?

 

Answer.

We can reverse the change if we use a pencil for drawing on the sheet. This change can be reversed by erasing the picture using an eraser.

 

Q5. Give examples to explain the difference between changes that can or cannot be reversed.

 

Answer.

There are a lot of changes that take place around us. Some of these changes can be reversed and some cannot be reversed. Examples of these changes are given in the below table.

 

Change	Can/cannot be reversed
Raw egg to boiled egg	Cannot be reversed
Flour to bread	Cannot be reversed
Wet clothes to dry clothes	Can be reversed
Woollen yarn to a knitted sweater	Can be reversed
Grain to its flour	Cannot be reversed
Cold milk to hot milk	Can be reversed
Milk to paneer	Cannot be reversed
Stretched rubber band to its normal size	Can be reversed
Ice cream to molten ice cream	Can be reversed

 

 

Q6. 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 immobilised. Can the change in POP be reversed?

 

Answer.

No, we cannot reverse this change because the change in POP is a chemical change.

 

Q7. A bag of cement lying in the open gets wet due to rain during the night. The next day the sun shines brightly. Do you think the changes, which have occurred in the cement, could be reversed?

 

Answer.

When a cement bag gets wet it forms a new substance after it is dried. This is a chemical change; hence this change cannot be reversed.

 

Q8. The formation of snow is a physical change. Explain.

 

Answer.

A change, in which a substance undergoes, a change in its physical properties, that is, shape, size, colour or state, is called a physical change. In this change now new substance is formed. Water exists in three states, that is, solid, liquid and gas. Since snow is the solid state of water, and no new substance is formed therefore the formation of snow is a physical change.

 

Q9. The burning of an incense stick is a chemical change. Explain?

 

Answer.

 

A chemical change is a change in which one or more substances are formed. The burning of any substance is a chemical change. The burning of an incense stick forms ash as a new substance therefore it is a chemical change.