Science - Class 7 (C ...

Q45. Classify the changes involved in 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 - _______________________

(g) Condensation of steam – ____________________

(h) Spoiling of food – __________________

(i) Burning of coal – _____________________

 

Q46. When a candle burns, both physical and chemical changes take place.

Identify these changes. Give another example of a familiar process in which both the chemical and physical changes take place.

 

Q47. Explain why burning of wood and cutting it into small pieces are considered as two different types of changes.

 

Q48. What happens when an iron nail is dipped in copper sulphate solution?

 

Q49. The gas we use in the kitchen is called liquified petroleum gas (LPG). In the cylinder it exist as a liquid. When it comes out from the cylinder it becomes a gas (Change – A) then it burns (Change – B). The following statements pertain to these changes. Choose the correct one.

(i) Process – A is a chemical change.

(ii) Process – B is a chemical change.

(iii) Both processes A and B are chemical changes.

(iv) None of these processes is a chemical change.

 

Q50. Anaerobic bacteria digest animal waste and produce biogas (Change – A). The biogas is then burnt as fuel (Change – B). The following statements pertain to these changes. Choose the correct one.

(i) Process – A is a chemical change.

(ii) Process – B is a chemical change.

(iii) Both processes A and B are chemical changes.

(iv) None of these processes is a chemical change.

 

Q51. Differentiate between physical and chemical change.

 

Q52. Describe how crystals of copper sulphate are prepared.