Short Answer Questions
Question 16: Osmosis is a special kind of diffusion. Comment.
Answer: The movement of particles from low concentration to high concentration is responsible for the diffusion in liquids and gases. In the case of osmosis the particles move from the low concentration to high concentration through the semi permeable membrane, this happens because of diffusion. Hence, osmosis is called a special kind of diffusion.
Question 17: Classify the following into osmosis/diffusion
- Swelling up of a raisin on keeping in water.
- Spreading of virus on sneezing.
- Earthworm dying on coming in contact with common salt.
- Shrinking of grapes kept in thick sugar syrup.
- Preserving pickles in salt.
- Spreading of smell of cake being baked throughout the house.
- Aquatic animals using oxygen dissolved in water during respiration.
Answer: (a) Osmosis, (b) Diffusion, (c) Osmosis, (d) Osmosis, (e) Osmosis, (f) Diffusion, (g) Diffusion
Question 18: Water as ice has a cooling effect, whereas water as steam may cause severe burns. Explain these observations.
Answer: Water turns into ice when temperature decreases to 00C. Water turns into steam at 1000C when heat is supplied to water. Water as steam has more latent heat while water as liquid does not. Hence water as steam may cause severe burns while water as ice has a cooling effect.
Question 19: Alka was making tea in a kettle. Suddenly she felt intense heat from the puff of steam gushing out of the spout of the kettle. She wondered whether the temperature of the steam was higher than that of the water boiling in the kettle. Comment.
Answer: The boiling point of water is 1000C. The temperature of boiling water does not rise instead of continuous supply of heat, as the extra heat is supplied to the water is used to turn water into steam. Hence, steam has a lot of latent heat which can cause severe burn. That’s why Alka felt intense heat from the puff of steam gushing out of the spout of the kettle.
Question 20: A glass tumbler containing hot water is kept in the freezer compartment of a refrigerator (temperature < 0°C). If you could measure the temperature of the content of the tumbler, which of the following graphs (Fig.1.2) would correctly represent the change in its temperature as a function of time.
Answer: Figure (a)
The temperature of water falls to 00C first. Then it will be constant till all water turn into ice, then it will decrease.
Question 21: Look at Fig. 1.3 and suggest in which of the vessels A, B, C or D the rate of evaporation will be the highest? Explain.
Answer: Figure (c)
The rate of evaporation increases with the increase in surface area and wind speed. The surface areas of vessel C, A and D are similar but the wind speed is greater above the vessel C because of fan, hence the rate of evaporation will be highest in the vessel C.
Question 22: (a) Conversion of solid to vapour is called sublimation. Name the term used to denote the conversion of vapour to solid.
(b) Conversion of solid state to liquid state is called fusion; what is meant by latent heat of fusion?
Answer: (a) The conversion of vapour to solid without changing into liquid is known as ‘sublimation’. This process is also known as ‘deposition’.
(b) Latent heat of fusion is the heat required to melt the solid state to liquid state without increase in temperature.