THESE NOTES ARE PREPARED ACCORDING TO JKBOSE SYLLABI IN SIMPLIFIED AND CONCISE PATTERN
Exercises
1. Classify the changes involved in the following processes as physical or chemical changes:
Ans:
A. Photosynthesis : Chemical change.
B. Dissolving sugar in water: Physical change.
C. Burning of coal: Chemical change
D. Melting of wax: Physical change
E. Beating aluminum to make aluminum foil: Physical change
F. Digestion of food: Chemical change
2. State whether the following statements are true or false. In case a statement is false, write the corrected statement in your notebook.
a. Cutting a log of wood into pieces is a chemical change. (True/False)
Ans: False
b. Formation of manure from leaves is a physical change. (True/False)
Ans: False
c. Iron pipes coated with zinc do not get rusted easily. (True/False)
Ans: True
d. Iron and rust are the same substances. (True/False)
.
Ans: False
e. Condensation of steam is not a chemical change. (True/False)
Ans: True
3. Fill in the blanks in the following statements
A. When carbon dioxide is passed through lime water, it turns milky due to the formation of Calcium Carbonate (CaCO3).
B. The chemical name of baking soda is Sodium Bicarbonate. Or Sodium Hydrogen Carbonate
C. Two methods by which rusting of iron can be prevented are Painting and Galvanization.
D. Changes in which only Physical properties of a substance change are called physical changes.
4. When baking soda is mixed with lemon juice, bubbles are formed with evolution of a gas. What type of change is it? Explain.
Ans: The mixing of baking soda with lemon juice is a chemical change.
It is because when baking soda reacts with lemon juice, new substances such as carbon dioxide are formed.
5. 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 the physical changes take place.
Ans: When a candle burns, its wax melts which is a physical change.
However the wax near the flame reacts with oxygen to form carbon dioxide, soot, heat and light which is a chemicak change.
Other examples: Burning of LPG, Weathering of rocks, Digestion of food etc.
6. How would you show that setting of curd is a chemical change?
Ans: During the setting of curd, a new chemical substance is formed, hence it is a chemical change.
The new chemical substance is lactic acid.
7. Explain why burning of wood and cutting it into small pieces are considered as two different types of changes.
Ans: Burning of wood is a chemical change as wood reacts with oxygen to form new substances such as carbon dioxide, Soot, heat and light.
Cutting wood into small pieces is a physical change as no new substance is formed.
8. Describe how crystals of copper sulphate are prepared?
Ans: Crystals of Copper sulphate (CuSO4) are formed by the process of crystallization.
Copper sulphate powder is added into boiling cup of water till it is saturated.
The solution is filtered and allowed to cool. After sometime copper sulphate crystals start forming.
9. Explain how painting of an iron gate prevents it from rusting?
Ans: Rusting occurs when iron reacts with air and mositure present in the atmosphere.
When we paint iron gate, it stops iron from reacting with air and moisture and thus stops rusting.
10. Explain why rusting of iron objects is faster in coastal areas than in deserts?
Ans: Rusting occurs when iron reacts with air and mositure present in the atmosphere.
In coastal areas, there is lot of moisture present in the air as compared to desert areas. Hence, rusting of iron is faster in coastal areas than in deserts.
11. The gas we use in the kitchen is called liquified petroleum gas(LPG). In the cylinder it exists 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.
Ans: ii. Process-B is a chemical change.
12. Anaerobic bacteria digest animal waste and produce biogas (change-A). The biogas is then burnt as fuel (changeB). 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.
Ans: iii. Both processes A and B are chemical changes.
Choose the correct one:
13. Rust is
(a) Carbon dioxide (b) Iron
Ans:
A. Photosynthesis : Chemical change.
B. Dissolving sugar in water: Physical change.
C. Burning of coal: Chemical change
D. Melting of wax: Physical change
E. Beating aluminum to make aluminum foil: Physical change
F. Digestion of food: Chemical change
2. State whether the following statements are true or false. In case a statement is false, write the corrected statement in your notebook.
a. Cutting a log of wood into pieces is a chemical change. (True/False)
Ans: False
b. Formation of manure from leaves is a physical change. (True/False)
Ans: False
c. Iron pipes coated with zinc do not get rusted easily. (True/False)
Ans: True
d. Iron and rust are the same substances. (True/False)
.
Ans: False
e. Condensation of steam is not a chemical change. (True/False)
Ans: True
3. Fill in the blanks in the following statements
A. When carbon dioxide is passed through lime water, it turns milky due to the formation of Calcium Carbonate (CaCO3).
B. The chemical name of baking soda is Sodium Bicarbonate. Or Sodium Hydrogen Carbonate
C. Two methods by which rusting of iron can be prevented are Painting and Galvanization.
D. Changes in which only Physical properties of a substance change are called physical changes.
4. When baking soda is mixed with lemon juice, bubbles are formed with evolution of a gas. What type of change is it? Explain.
Ans: The mixing of baking soda with lemon juice is a chemical change.
It is because when baking soda reacts with lemon juice, new substances such as carbon dioxide are formed.
5. 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 the physical changes take place.
Ans: When a candle burns, its wax melts which is a physical change.
However the wax near the flame reacts with oxygen to form carbon dioxide, soot, heat and light which is a chemicak change.
Other examples: Burning of LPG, Weathering of rocks, Digestion of food etc.
6. How would you show that setting of curd is a chemical change?
Ans: During the setting of curd, a new chemical substance is formed, hence it is a chemical change.
The new chemical substance is lactic acid.
7. Explain why burning of wood and cutting it into small pieces are considered as two different types of changes.
Ans: Burning of wood is a chemical change as wood reacts with oxygen to form new substances such as carbon dioxide, Soot, heat and light.
Cutting wood into small pieces is a physical change as no new substance is formed.
8. Describe how crystals of copper sulphate are prepared?
Ans: Crystals of Copper sulphate (CuSO4) are formed by the process of crystallization.
Copper sulphate powder is added into boiling cup of water till it is saturated.
The solution is filtered and allowed to cool. After sometime copper sulphate crystals start forming.
9. Explain how painting of an iron gate prevents it from rusting?
Ans: Rusting occurs when iron reacts with air and mositure present in the atmosphere.
When we paint iron gate, it stops iron from reacting with air and moisture and thus stops rusting.
10. Explain why rusting of iron objects is faster in coastal areas than in deserts?
Ans: Rusting occurs when iron reacts with air and mositure present in the atmosphere.
In coastal areas, there is lot of moisture present in the air as compared to desert areas. Hence, rusting of iron is faster in coastal areas than in deserts.
11. The gas we use in the kitchen is called liquified petroleum gas(LPG). In the cylinder it exists 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.
Ans: ii. Process-B is a chemical change.
12. Anaerobic bacteria digest animal waste and produce biogas (change-A). The biogas is then burnt as fuel (changeB). 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.
Ans: iii. Both processes A and B are chemical changes.
Choose the correct one:
13. Rust is
(a) Carbon dioxide (b) Iron
(c) Oxygen (d) Iron oxide.
Ans: d. Iron oxide.
14. Which of the following is not a physical change?
(a) Rusting of iron (b) Melting of ice
(c) Freezing of water (d) Dissolving sugar in water.
Ans: a. Rusting of iron.
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Ans: d. Iron oxide.
14. Which of the following is not a physical change?
(a) Rusting of iron (b) Melting of ice
(c) Freezing of water (d) Dissolving sugar in water.
Ans: a. Rusting of iron.
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