ADDITIONAL QUESTIONS AND ANSWERS:
1. Define matter.
Ans: Anything that occupies space and has mass is called matter.
2. State different states of matter with an example.
Ans: Matter has 3 different states Solid liquid gas Ice water steam
3. What is diffusion.
Ans: The intermingling of molecules of one substance with that of the other is called diffusion.
4. What happens to the rate of diffusion if the temperature is increased.
Ans: With increased temperature, the rate of diffusion also increases as the particles gain kinetic energy and vibrate more.
5. Define melting point.
Ans: The temperature at which a solid melts to become liquid at the atmospheric pressure is called its melting point.
6. Define boiling point.
Ans: The temperature at which a liquid starts boiling at the atmospheric pressure is known as it’s boiling point.
7. Define latent heat of vaporization.
Ans: Latent heat of vaporization is the heat energy required to change 1 kg of a liquid to gas atmospheric pressure at its boiling point.
8. Define latent heat of fusion.
Ans: Latent heat of fusion is the amount of heat energy required to change 1 kg of solid into liquid at its melting point.
9. Define sublimation.
Ans: Sublimation is the change of gaseous state directly to solid state without going through liquid state and vice-versa.
10. What is dry ice.
Ans: Solid carbon dioxide is obtained by cooling and applying pressure on carbon dioxide gas. It does not melt so it is called dry ice.
11. What is humidity.
Ans: The air holds water vapour, this air with water is called humid air and the phenomenon is called humidity.
12. Give two properties of solid.
Ans: (1) Solids have fixed shape and are rigid.
(2) Solids cannot be compressed .
13. What will happen if the pressure is reduced on solid carbon dioxide (dry ice)
Ans. If the pressure is reduced on solid carbon dioxide it will directly change into gaseous state without melting.
14. Name any three substances that show sublimation.
Ans: Ammonium chloride, camphor and naphthalene balls are three substances that show sublimation
15. Sponge is solid, but we can still compress it. Why.
Ans: Sponge is a solid with minute pores in it. When we press the sponge the air present in these pores is released out and hence we are able to compress it. 16. What is atmospheric pressure.
Ans: The pressure of air in atmosphere is called atmospheric pressure. 17. What is Kelvin.
Ans: Kelvin is the SI unit of temperature (0°C = 273 K).
18. Give two examples of diffusion.
Ans: Milk drops dissolved in water and perfume sprayed in a room.
19. Give the temperature at which water exists in two different states.
Ans: At 0°C water can be in solid or in liquid state. At 100°C water can be in liquid or in gaseous state.
20. Why do we see water droplets collected on the outer surface of a glass container, containing ice.
Ans: The water vapour present in air, comes in contact with the cold outer surface of the container thereby condensing it to form water droplets.
21. Explain why solids have fixed shape but liquids and gases do not have fixed shape
Ans: Solids have fixed shape due to strong intermolecular force of attraction between them. The liquids and gases have molecules with less intermolecular force of attraction and hence they can flow and take shape of the container.
22.Liquids and gases can be compressed but it is difficult to compress solids. Why
Ans: Liquids and gases have inter molecular space, on applying pressure externally on them the molecules can come closer thereby minimizing the space between them. But in case of solids there is no inter molecular space in between then to do so.
23. A balloon when kept in sun, bursts after some time. Why.
Ans: The balloon has air filled in it. The balloon when kept in sun gets heated and the air inside it also gets heated. The molecules of air get energy, and vibrate faster thereby exerting large force on the walls of the balloon. Due to this expansion of gases the balloon bursts.
24. Why do people perspire a lot on a hot humid day.
Ans: On a hot, humid day, due to the heat our body starts sweating for the cooling mechanism i.e., by evaporation to get a cooling effect. But the air cannot hold any more water on a humid day and therefore the sweat or perspiration is seen.
25. Distinguish between evaporation and boiling.
Ans:
| Evaporation | Boiling |
| 1. Evaporation is a surface phenomenon. 2. It is a slow process. 3. It takes place at all temperatures. |
i) Boiling is a bulk phenomenon. ii) It is a fast process. iii) It takes place at a definite temperature. |
26. Why is it advisable to use pressure cooker at higher altitudes.
Ans: At higher altitudes, the atmospheric pressure is low and the water boils very fast and evaporates at faster rate so pressure is required to increase the cooking process and this is done by using pressure cooker which increases the pressure inside the container and cooks the food faster.
27. What are fluids.
Ans: The states of matter that can flow due to less inter molecular force of attraction, are liquids and gases and are called as fluids.
28. One kg cotton and one kg sand, which is denser. Why.
Ans: One kg sand is denser than 1 kg cotton because density = mass/volume. The volume required by cotton is more than the sand and density and volume are inversely proportional.
29. Why is water liquid at room temperature.
Ans: At room temperature, the molecules of water have some inter molecular force of attraction and the room temperature cannot provide sufficient heat for these molecules to overcome their force of attraction and therefore remain in liquid phase.
30. Cotton is a solid but it floats on water. Why.
Ans: Cotton has large number of pores, in which air is trapped. Hence reducing its density and increasing the volume. Therefore cotton floats on water. But when these pores get filled with water it starts sinking.
31. Why arc solids generally denser than liquids and gases.
Ans: Density of a substance is given by a formula= Mass/Volume In case of solids the molecules are tightly packed and hence large mass is concentrated in very small volume. Hence their density is more. But in case of liquids and gases, their molecules have inter molecular space and hence they don’t have large mass concentrated in small volume. So the density of solids is generally more than that of the liquids and gases.
32. On a hot sunny day, why do people sprinkle water on the roof or on open grounds
Ans: During hot sunny day, the surface of roof or ground absorbs large amount of heat and remains hot. On sprinkling water on these surfaces, the water absorbs large amount of heat from the surface due to its large latent heat of vaporization thereby allowing the hot surface to cool.
33. On a hot sunny day why do we feel pleasant sitting under a tree.
Ans: Tree has lot of leaves which constantly show transpiration. Transpiration is loss of water through small tiny pores of leaves called stomata. When this water comes on the surface of leaf the water evaporates thereby causing cooling effect. Therefore we feel pleasant sitting under the tree on a hot sunny day.
34. Name the factors that affect evaporation.
Ans: The rate of evaporation will increase with
(1) An increase of surface area,
(2) An increase of temperature,
(3) A decrease in humidity,
(4) An increase in wind speed.
35. The melting point of ice is 273.16 K. What does this mean. Explain in detail.
Ans: Ice is solid at 0°C i.e. 273° K. The molecules of ice are tightly packed. These molecules have to overcome the force of attraction with which they are held and hence they gain this heat from the surrounding. But the temperature remains the same as their energy is used to overcome the force of attraction between the particles. The particles starts vibrating freely and reaches a stage when the solid ice melts and is converted to liquid state at the same temperature i.e. 273 K.
36. How is the high compressibility property of gas useful to us.
Ans: The gases have high compressibility. This property is used in the following situation:
(1) LPG (Liquefied Petroleum Gas) is a fuel which is made up of petroleum gas. On compressing this petroleum gas it forms liquid.
(2) Oxygen cylinders in the hospitals have compressed gas filled in it.
(3) CNG (Compressed Natural Gas) is a natural gas, methane, which is compressed and used as a fuel in vehicles and at home.
37. With the help of an example, explain how diffusion of gases in water is essential.
Ans: The gases from the atmosphere diffuse and dissolve in water. Gases like oxygen and carbon dioxide diffuse in water , are essential for the survival of aquatic animals and plants. Animals breathe in this oxygen dissolved in water for their survival and plants can use carbon dioxide dissolved in water for photosynthesis.
38. Name the property of gases due to which it is possible to fill CNG in cylinders for using as fuels in cars .
Ans : Gases can be easily compressed and it is possible to fill CNG in cylinders for using as fuels in cars .
39. Does evaporation cause a physical change or a chemical change ?
Ans : Evaporation causes a physical change .
40. How does spreading of wet clothes quicken their drying ? Explain .
Ans : It increases exposed surface area due to which water gets evaporated at a faster rate .
41. List any two properties of particles of matter .
Ans : i) They attract each other .
ii) The particles of matter are extremely small in size which cannot be seen even with a powerful microscope .
42. Gases exert pressure on the walls of the container . Why ?
Ans : The molecules of gases collide with themselves as well as with the walls of container and so they exert pressure on the walls of the container.
43. What is tincture of iodine ?
Ans : A solution of iodine in alcohol is known as ‘tincture of iodine’ .
44. Evaporation causes cooling . Why ?
Ans : Evaporation needs heat energy which it takes from surroundings and leads to decrease in temperature , i.e. cooling takes place .
45. We feel cold when we touch a piece of ice . Why ?
Ans : It is because ice takes heat from our body and therefore , we fell cold .
46. Define the following terms .
a) Latent heat of fusion .
b) Melting point .
c) Fusion.
Ans : a) Latent heat of fusion : The amount of energy that is required to change 1 kg of a solid into liquid at atmospheric pressure without any change of temperature at its melting point is called latent heat of fusion .
b) Melting point : The temperature at which solid changes into liquid completely is called melting point . Melting point of solids gives indication of the strength of intermolecular forces of attraction . Higher the melting point , more will be intermolecular forces of attraction .
c) Fusion (Melting) : The process in which solid changes into liquid is called melting . It is also called fusion .
47. What is full form of CNG ? Mention its one property which makes it so important
Ans : Compressed Natural Gas (CNG) . It does not create pollution on combustion and it is clean fuel which makes it so important .
48. Why mixture does not have a fixed melting or a fixed boiling point ? Give two reasons .
Ans : i) It does not have fixed composition .
ii) It does not have uniform ordered arrangement of particles .