Question

1. Cotton is solid but it floats on water. Why?

2. Why are solids generally denser than liquids and gases?

3. Name the factors that affect evaporation.

4. How is the high compressibility property of gas useful to us?

5. With the help of an example, explain how diffusion of gases in water is essential?

6. On a hot sunny day, why do people sprinkle water on the roof or open ground?

7. Why to people perspire a lot on a hot humid day?

8. A balloon when kept in sun, bursts after some time. Why?

9. Pressure and temperature determine the state of a substance. Explain this in detail.

10. Explain giving examples the various factors on which rate of evaporation depends.

Answer 1

1. Because Cotton is less denser than water.
2. Because molecules of solids are closely packed than solids and liquids.
3. Surface area, temperature, humidity.
4. It helps us store a lot of gas in small container.
5. Diffusion of gases in water enables the fishes to breathe in water.
6. To make the surroundings cool by evaporation process. Since Evaporation is a cooling process, it makes the surroundings cool.
7. The sweat on our body could not escape in to the atmosphere through Evaporation. Humidity is a factor that effects Evaporation.
8. Sun light heats up the air in the balloon, and this pierces the surface of balloon and so it bursts.
9. Yes it is true. As pressure and temperature increases, ice melts.
10. Surface area, temperature, humidity.

Answer 2

heya..

here are your answers..

1)

=cotton is solid but floats on water because
1) the upthrust applied by water is more than cotton's weight
2) water is more dense than cotton

........
2)

=solids are generally denser than liquids and gases because they have less intermolecular space and more force of attraction between the particles..thus more is collected in less volume...do it is more dense
..../
3)

=
factors affecting evaporation are-

1) surface area

2) temperature

3) humidity

4) wind speed
....

4)

=for ex.. gas are highly compressible as they have large intermolecular space between them..
for example.. we can compress gas and fill in the cylinders.. (LPG)
......
5)

= 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.
.....
6)

= because when water us sprinkled over the roof, because of the warmed surface the evaporation occurs faster ..which results in fast cooling
.....
7)
= On a hot, humid day, due to the heat our body starts sweating for the cooling mechanism i.e., by evaporation and gets cooling effect. But the air cannot hold any more water on a humid day and therefore the sweat or perspiration is seen.
.....

8)

= balloon when kept in sun bursts after some time because outside the temperature is high and due to that the kinetic energy increases and the molecules of gas particles inside exerts a pressure on the walls of theballoon so it will continue to expand and there a stage will come that the balloon will burst.
.....


9)
(1) Any matter i.e., solid, liquid or gas when experiences an increase in temperature then they change state

Take ice cubes in a beaker or heat them slowly, the temperature increases and the ice melts to form liquid. Heat this liquid further it will become steam.
(2) On lowering down the temperature of any matter, show change in their state.

Take the steam that is coming out of a boiling water and allow it to cool down, it condenses to form water and on further cooling of this water we get ice.
(3) On applying pressure and reducing temperature we can liquefy gases or change them into solid.
Example: Take carbon-dioxide gas, reduce its temperature and apply lot of pressure on it so that it changes into solid carbon dioxide, called dry ice, which is used as refrigerant for cooling.
If the pressure on it is decreased it directly changes into gas.
In LPG cylinders, the petroleum gas is cooled and with lot of pressure changes it into liquid state.
While using this LPG, we release the pressure exerted on it and hence it comes out in the form of gas.
=
......
10)

= factors affecting evaporation are-

1) surface area

if the surface area increases.rate of .evaporation also increases...ex. when we increase the surface area of clothes..

2) temperature
ex..on hot dry day ..when we sprinkle water over the roof it evaporates fastly

3) humidity
if humidity increases the rate of evaporation decreases...
for ex.. in eainy seasons..the clothes are hardly dried..

4) wind speed
....with increase in windspeed rate of evaporation increases..
ex.. while eating, hot food kept under fan cools fastly..

hope helped..