NCERT Class 6 Science Chapter 6 Changes Around us

Chapter 6 Changes Around us

Question 1: To walk through a waterlogged area, you usually shorten the length of your dress by folding it. Can this change be reversed?
Answer: Yes, this change can be reversed.

Question 2: You accidentally dropped your favourite toy and broke it. This is a change you did not want. Can this change be reversed?
Answer: No, this change can’t be reversed.

Question 3: Some changes are listed in the following table. For each change, write in the blank column, whether the change can be reversed or not.

Answer:
a) The sawing of a piece of wood - No
b) The melting of ice candy - Yes
c) Dissolving sugar in water - Yes
d) The cooking of food - No
e) The ripening of a mango - No
f) Souring of milk - No

Question 4: A drawing sheet changes when you draw a picture on it. Can you reverse this change?
Answer:
• If the drawing is made with a pencil then it can be erased and we will get the original sheet back. So, we can reverse the change.
• But if a pen, paint, oil /water colors are used to draw the picture, change cannot be reversed.

Question 5: Give examples to explain the difference between changes that can or cannot be reversed.
Answer:
• Changes that can be reversed:
→ Writing with a pencil.
→ Making ice from water.
→ Inflating a balloon

• Changes that can’t be reversed:
→ Making curd from milk.
→ Burning of paper.
→ Ripening of fruit

Question 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 immobilised. Can the change in POP be reversed?
Answer: No, the change in plaster of Paris cannot be reversed. When water is added to POP, it undergoes a chemical change.  Its composition changes and is converted into another substance. Since it is a chemical change, so it cannot be reversed.

Question 7: 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: No, these are irreversible chemical changes.