Class 9 Science

Matter

Exemplar Problem

Part 2

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

1. Swelling up of a raisin on keeping in water.
2. Spreading of virus on sneezing.
3. Earthworm dying on coming in contact with common salt.
4. Shrinking of grapes kept in thick sugar syrup.
5. Preserving pickles in salt.
6. Spreading of smell of cake being baked throughout the house.
7. 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.

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.