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Revision Question Bank
Matter in Our Surrounding
1.
Why does the smell of hot cooked food reach you several meters away within second?
Solution:
It is because the vapours of hot food diffuse in air readily and reach us several metres
away within second.
2.
How does spreading of wet clothes quicken their drying? Explain.
Solution:
It increases exposed surface area due to which water gets evaporated at faster rate.
3.
Write one important characteristic property of particles of matter.
Solution:
Particles of matter attract each other.
4.
Why do people in villages use earthen pots in summer to cool water?
Solution:
It is because evaporation takes place at surface of earthen pot, which causes cooling.
5.
What is the physical state of water at the following temperatures?
(a)25°C
(b)0°C
(0100°C
Solution:
(a) H2O is in liquid state at 25°C.
(b) It is in solid state at 0oC.
(c) It is in vapour (gas) state at 100oC.
6.
(a) Arrange the following substances in the increasing order of force of attraction
between the particles water, hydrogen and sand.
(a) Why does the temperature remain constant at the melting point?
(b) Which property of gases makes it possible to fill large volume of gases in small
cylinders?
(c) 'Water as ice has a cooling effect whereas water as steam may cause severe burns'.
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Explain these observations.
Solution:
(a) Hydrogen < water < sand
(b) It is because latent heat of fusion overcomes inter particle force of attraction.
(c) Gases can be compressed easily.
(d) Ice takes latent heat effusion from the body and causes cooling effect whereas;
steam has very high energy because it has latent heat of vaporization. Therefore, it causes
severe burns.
7.
Comment on the following statements
(a) Evaporation produces cooling.
(b) Rate of evaporation of an aqueous solution decreases with increase in humidity.
(c) Sponge though compressible is a solid.
Solution:
(a) In evaporation, surface molecules take heat from surrounding and cause cooling
effect.
(b) If humidity is high, then air already has lot of water vapours. It will not take more
water vapours easily. Therefore, the rate of evaporation will be slow.
(c) Sponge has small holes in which air is filled. The material is also not so rigid. Air
escapes when we press it, that is why it can be compressed but it is solid.
8.
Explain the factors on which rate of evaporation depends?
Solution:
Factors on which rate of evaporation depends:
(i) Surface area (ii) Temperature (iii) Humidity (iv) Wind speed.
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Chapter Test {Matter in Our Surrounding}
M: Marks: 30
1.
M:Time: 40Min.
Give reasons for the following:
[2]
(a) A sponge is a solid but can be easily compressed.
(b) Clothes dry faster on a windy day.
Solution:
(a) Sponge contains pores in which air is trapped. On pressing, the air which is trapped,
moves out and when we release the pressure, the air re-enters giving the original shape.
(b) The kinetic energy of the wind removes the water molecules on the surface of the
clothes, that helps in drying of clothes.
2.
Answer the following questions:
[3]
(a) For any physical state of a substance, the temperature remains constant
during its change of state.
(b) Water kept in an earthen pot becomes cool in summer.
(c) We are able to sip hot tea from a saucer rather than from a cup.
Solution:
(a) During a change in physical state of a substance, the temperature remains constant.
For example, when water changes into steam at 100°C; the temperature remains constant
at 100°C until the whole of water has been converted into steam, after which the
temperature starts rising.
(b) The earthen pot is porous, water taken inside the pot comes out on the outer surface.
Evaporation of water takes place.
Evaporation is always accompanied by cooling. This makes the water cool inside the pot.
(c) Saucer has a bigger surface area than the cup. The tea taken out into the saucer has a
lower temperature as compared to that in the cup. Therefore, we are able to sip hot tea
from the saucer and not from the cup.
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3.
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(a) Differentiate between three states of matter on the basis of the following
properties.
[3]
(i) Intermolecular forces. (ii) Arrangement of molecules.
(b) Liquid generally has lower density as compared to solids. But you must
have observed that ice floats on water. Give reason.
Solution:
Solid State There are strong intermolecular forces between the particles of a solid, which
keep the particles close to one another. The particles of the solid are arranged in a closed
packing manner. They have a fixed shape.
Liquid State The intermolecular force of attraction between the particles is smaller as
compared to those in solids. The particles of a liquid are able to move around. They take
the shape of the vessel in which they are placed. However, liquids have a fixed volume.
Gaseous State The particles of a gaseous substance are free to move about because there
is minimum intermolecular force of attraction between them. They have no fixed shape
and no fixed volume. They fill the whole of the vessel in which they are taken.
(b) Because of lower intermolecular force of attraction, particles of liquid move about
freely. There is a space between different particles. Therefore, they possess lower density.
However in the case of ice, which is the solid form of water, there are vacant spaces due
to a particular structure. Therefore, ice is lighter than water. Hence, ice floats on water.
4.
Answer the following questions:
[3]
(a) Differentiate between three states of matter on the basis of the following
properties.
(i) Intermolecular forces. (ii) Arrangement of molecules.
(b) Liquid generally has lower density as compared to solids. But you must have
observed that ice floats on water. Give reason.
Solution:
Solid State There are strong intermolecular forces between the particles of a solid, which
keep the particles close to one another. The particles of the solid are arranged in a closed
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packing manner. They have a fixed shape.
Liquid State The intermolecular force of attraction between the particles is smaller as
compared to those in solids. The particles of a liquid are able to move around. They take
the shape of the vessel in which they are placed. However, liquids have a fixed volume.
Gaseous State The particles of a gaseous substance are free to move about because there
is minimum intermolecular force of attraction between them. They have no fixed shape
and no fixed volume. They fill the whole of the vessel in which they are taken.
(b) Because of lower intermolecular force of attraction, particles of liquid move about
freely. There is a space between different particles. Therefore, they possess lower density.
However in the case of ice, which is the solid form of water, there are vacant spaces due
to a particular structure. Therefore, ice is lighter than water. Hence, ice floats on water.
5.
Answer the following questions
[3]
(a) Solids and liquids are collectively known as condensed phases. Explain.
(b) At what temperature solid ice and liquid water exist together?
(c) Why are gases compressible but not the liquids?
Solution:
(a) Insecticide - DDT or Malathion.
(b) Fungicide –Aluminium phosphids or methyl bromide.
(c) Weedicide –2, 4–D or atrazine.
6.
Explain the following
(a) Fusion
(b) Kelvin
(c) Latent heat
(d) Latent heat of fusion
[5]
(e) Atmospheric pressure
Solution:
(a) Fusion The process of melting, i.e., conversation of solid into liquid state is called
fusion.
(b) Kelvin Kelvin is the SI unit of temperature. 0oC = 273.16 K. For the sake of
convenience 0°C is taken equal to 273 K. Thus temperature in Kelvin
(K) = Temperature in Celsius (°C)+273.
(c) Latent heat On converting a solid to liquid (fusion) or liquid to gas (evaporation), the
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heat energy is used up to overcome the force of
attraction between the particles without showing any change in temperature. Since, this
heat energy is hidden in the bulk of the matter, it is called latent heat. The world latent
means hidden.
(d) Latent heat of fusion The amount of heat energy needed to convert 1 kg (1000 g) of a
solid into liquid at the atmospheric pressure at its melting point is called latent heat of
fusion.
(e) Atmospheric pressure The pressure of air in atmosphere is known as atmospheric
pressure.
At sea level, the atmospheric pressure is 1 atmosphere, which is called normal
atmospheric pressure. 1 atmosphere = 1.01 ×105 pascal.
7.
(a) What happens to sugar when it is dissolved in water? Where does the sugar go? What
information do you get about the nature of matter from the
[5]
dissolution of sugar in water?
(b) Which type of compounds can be purified by sublimation?
Solution:
(a) When sugar is dissolved in water, its crystals break off to give its tiny particles. The
sugar particles go into the spaces between the particles of water and mix with them to
form sugar solution.
From the dissolution of sugar in water we infer that
(i) The matter consisting of sugar and water is made up of small particles.
(ii) The particles of matter (water) have spaces between them.
(b) The compounds, which sublime themselves but contain impurities, which
cannot be sublimed, can be purified by the process of sublimation.
8.
Answer the following questions
[3]
(a) Liquids generally have lower density as compared to solids. But you must have
observed that ice floats on water. Find out why?
(b) What is the physical state of water at
(i) 250°C
(ii) 100°C
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(c) For any substance, why does the temperature remain constant during the change of
state?
Solution:
(a) The mass per unit volume of a substance is called density (density = mass/volume).
As the volume of a substance increases, its density decreases.
Though ice is a solid, it has large number of empty spaces between its particles. These
spaces are larger as compared to the spaces present between the particles of water. Thus,
the volume of ice is greater than that of water. Hence, the density of ice is less than that of
water. A substance with lower density than water can float on water. Therefore, ice floats
on water.
(b)(i) Water at 250°C exists in gaseous state.
(ii) At 100°C, water can exist in both liquid and gaseous form. At this temperature, after
getting the heat equal to the latent heat of vaporisation, water starts changing from liquid
state to gaseous state.
(c) During a change of state, the temperature remains constant. This is because all the
heat supplied to increase the temperature is utilized in changing the state by overcoming
the forces of attraction between the particles. Therefore, this heat does not contribute in
increasing the temperature of the substance.
9.
State some factors that affect rate of evaporation of water. Discuss how each one of these
factors affects the rate of evaporation.
[3]
Solution:
(a) Surface Area Greater the surface area, more will be the rate of evaporation, as it is
surface phenomenon. There will be more number of molecules, on the surface which will
change into vapours easily.
(b) Temperature With the increase in temperature, the rate of evaporation increases. It
is because, more number of particles gain enough kinetic energy to go to vapour state.
(c) Wind Speed More the wind speed, more will be the rate of evaporation, as more
molecules
will go in vapour state easily.
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(d) Humidity The air around us cannot hold more than a limited amount of water vapours
at a given temperature. When the amount of water in air is already high, the rate of
evaporation decreases, i.e., decrease in humidity leads to increase in the rate of
evaporation.
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