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Wednesday, May 18, 2011

9th Chemistry Matter in Our SurroundingsTest Paper

Class IX, Chemistry Questions Paper: Chapter 1: Matter in Our Surroundings
Q1: Convert 570 K into Celsius scale. (1 mark)
Q2: What is humidity? (1 mark)
Q3: Give reasons:
a. The smell of hot sizzling food reaches you several meters away, but to get the smell from cold food you have to go close.
b. A diver is able to cut through water in a swimming pool. (2 mark)
Q4: Which phenomenon occurs during the following changes? (2 mark)
a. Size of naphthalene ball decreases             b. Drying of clothes
Q5: Define the following (3 mark)
a. Condensation                   b. Latent heat of fusion c. freezing
Q6: Explain why gases are easily compressible as compared to liquids and solids. (3 mark)
Q7: Why do plants require more leaves during summer? (3 mark)
Q8: List any four factors on which evaporation depends? Explain in short any three factors. (5 marks)
Solution:
Ans 1: Temperature in oC = Temperature in Kelvin -273 (1/2mark)
Therefore, Temperature in oC = 570 K -273= 297 oC (1/2 mark)
Ans 2: Presence of water vapour in air is called humidity. (1 mark)
Ans 3: 
a. The particles of hot sizzling food have more kinetic energy and thus diffuse rapidly in the air as compared to cold food which possesses less kinetic energy. (1 mark)
b. Particles of water contain spaces between them. Hence a diver is easily able to cut through water in a swimming pool (1 mark)
Ans 4: a. Sublimation (1 mark)           b. Evaporation (1 mark)
Ans 5: a. Condensation: Process in which a gas changes into liquid state by giving out heat at constant temperature is called Condensation. (1 mark)
b. Latent heat of fusion: It is the amount of heat energy required to change 1 kg of solid into liquid at its melting point. (1 mark)
c. Freezing: Process in which a liquid changes into solid by giving out heat at constant temperature is called Freezing. (1 mark)
Ans 6: Gases are easily compressible because they have weak forces of attraction between the molecules and have more intermolecular space. (1 mark)
In liquids there is a stronger force of attraction between the molecules and less intermolecular space as compared to gases. Hence, they are not as easily compressible as compared to gases. (1 mark)
In solids forces of attraction among molecules is strongest as compared to both liquids and gases. Further intermolecular space is least as compared to liquids and gases. Hence, they are least compressible as compared to gases and liquids. (1 mark)
Ans7: Evaporation of water from leaves of plants is called transpiration. Transpiration helps the plants to keep themselves cool. During summers as the temperature increases more transpiration takes place in order to keep themselves cool. Therefore, more leaves are required for transpiration. Hence, plants acquire more leaves during summer. (3 marks)
Ans8: The rate of evaporation depends on following factors:
1) Surface area exposed to atmosphere (1/2 mark)         2) Temperature (1/2 mark) 
3) Humidity (1/2 mark)                                                   4) Wind speed (1/2 mark)
1) Surface area exposed to atmosphere: Since evaporation is a surface phenomenon, therefore, it increases with an increase in surface area. (1 mark)
2) Humidity: The air around us cannot hold more than a definite amount of water vapour at a given temperature. If the amount of water in air is already high, the rate of evaporation decreases. So, evaporation decreases with increase in humidity. (1 mark)
3) Wind speed: With the increase in wind speed, the particles of water vapour move away with the wind, decreasing the amount of water vapour in the surroundings. This results in a faster rate of evaporation. So, evaporation increases with the increase in wind speed. (1 mark)

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