Page 2 - CBW

e) If Assertion and Reason both are incorrect.

6. Assertion (A): Change in the colour of copper vessels due to reaction with moist air is a
chemical change.
Reason (R): It forms a green-coloured layer of copper carbonate.
7. Assertion (A): Phenolphthalein remains colorless in acidic solution.
Reason (R): Phenolphthalein turns pink in basic solution.
8. Give reason for the following:

a) Burning of magnesium ribbon is a chemical change.
b) Formation of gas bubbles take place when vinegar and baking soda react together.

9. A candle is lit. The wax melts and the wick burns.

a) Which part of this process is a chemical change?
b) Why is melting of wax not considered as a chemical

change.

10. A farmer leaves iron tools outside in the rain. After a few days, they turn reddish-brown in
colour.

a) What is the name of the process that has taken place?
b) Is this process a physical or a chemical change? Explain.

11. Priya cut an apple and wanted to eat it for
lunch. But then she started doing her
homework and forgot about the apple.
Later she found that the apple had turned
brown.

Explain this observation.

12. Fill in the blanks with suitable words:
a) A change in state like boiling, melting, or freezing is considered a __________ change as
no __________ is formed.
b) When vinegar is mixed with baking soda, bubbles of __________ gas is formed, indicating
a __________ change.