When 50 gram of sugar is dissolved in 100ml of water there is no increase in volume why Class 9?

• Answer:

                 This observation indicates that particles of water have spaces between them into which sugar particles fit.        
  

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Page 2

• Answer:

                                                  Oxygen < water < sugar                           
  

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Page 3

• Answer:

                                The physical state of water at:                                           (a) 25°C is liquid       (b) Solid and liquid forms     are in equilibrium (c) Liquid and vapour forms are in equilibrium.
  

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Page 4

• Answer:

                 The water vapour present in the air comes in contact with cold surface of the glass, loses its energy and gets converted into droplets of water.
  

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Page 5

• Answer:

                 Density of a substance is defined as the mass per unit volume. Its SI unit is kgm-3.
  

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Page 6

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Page 7

• Answer:

                 In gases, the particles move randomly at high speed and they collide with the walls of the container
  

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Page 8

• Answer:

                 The temperature remains constant during the change of state because the heat supplied to the substance is used up in overcoming the intermolecular forces between the particles.
  

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Page 9

• Answer:

                 Atmospheric gases can be liquefied by applying pressure and reducing temperature.
  

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Page 10

• Answer:

                 On a dry day, humidity decreases and the rate of evaporation increases. Thus, it results in more cooling.
  

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Page 11

• Answer:

                 Glycerol < water < ethyl alcohol < diethyl ether  
  

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Page 12

• Answer:

                  When water is converted into ice, its volume expands about 10% in comparison to the volume of water. Thus, ice occupies more space. As a result, its density decreases and it floats on water.
  

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Page 13

• Answer:

                 (a) (i) Water at room temperature is a liquid because the intermolecular forces are strong enough to keep its particles bound to each other. (ii) It has fixed volume but not fixed shape. (b} (i) It has fixed shape and volume. (ii) It cannot flow.
  

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Page 14

• Answer:

           

  
  (i) Take   crystals   of ammonium chloride in a china dish.                      (ii) Put the china dish on a tripod stand               chloride with wire gauze.                    (iii) Put an inverted funnel on the china   Ammonium dish and insert a cotton plug in the stem of the funnel.           (iv] Heat the china dish on a low flame.      (v] In the inside of the funnel white deposits of ammonium chloride is seen which directly converts into gaseous state and then solidifies
  

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Page 15

• Answer:

                 The ice at 273 K is more effective in cooling than water because particles in ice at 273K have less energy as compared to particles in water at the same temperature.
  

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Page 16

• Answer:

                 A : Fusion or melting                             B : Vaporization or boiling  C : Condensation                      D : Solidification or freezing          E : Sublimation                         F : Sublimation                                             
  

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Page 17

• Answer:

                 When we place few crystals of potassium permanganate in a beaker containing water, we get two distinct layers?colourless water at the top and pink colours the bottom. After few minutes, pink colour spreads and whole solution turns pink due to diffusion. Since potassium permanganate is a solid substance, does not possess so much space. Water molecules due to liquid state, collide with solid particles and intermix due to sufficient space between molecules.
  

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Page 18

• Answer:

                 The temperature remains constant during the melting of ice because the heat supplied or absorbed at the melting point is used up in overcoming the intermolecular forces of attraction. Thus, heat is absorbed by ice without showing any increase in temperature.            
  

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Page 19

• Answer:

                                     (i) Rate of evaporation increases with rise in temperature. (ii) Evaporation is more when exposed surface area is more. (iii) Less evaporation if moisture content is high in the air. (iv) Rate of evaporation increases if wind speed increases.
  

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Page 20

• Answer:

                 Steam at 100°C is better for heating purposes than water at 100°C because the energy of 1 kg of steam at 100°C is 22.6 X 105joule which is more than that of 1 kg of water at the same temperature.
  

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Page 21

• Answer:

                 Conditions that can increase the rate of evaporation of water are: (a) An increase in the surface area by spreading the shirt. (b) An increase in the temperature by putting the shirt under the sun. (c) Increase in the wind speed by spreading it under the fan.
  

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Page 22

• Answer:

                 We should wear pure cotton clothes and preferably of white colour, because cotton fibres absorb perspiration which causes the cooling effect. Secondly, white colour clothes are poor absorbers of heat.
  

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Page 23

• Answer:

                 (a) 293K = (293 - 273) °C = 20°C              (b) 470k = (470-273) °C  = 197 °C
  

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Page 24

• Answer:

                 (a) 25°C = 25 + 273 = 298 K (b)373°C = 373 + 273 = 646 K
  

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Page 25

• Answer:

                 When a person has fever, his body temperature becomes more than the normal body temperature. If we put strips of wet cloth on the forehead of a person suffering from high fever, the water evaporates taking heat from the body. Thus, moist strips will lower his body temperature.
  

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Page 26

• Answer:

                 The particles of every matter has a force attracting them. This force keeps the particles together in a matter. In case of water, the force of attraction between particles is less in comparison to solids. Thus, water molecules flow easily giving way to a diver.
  

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