1. TOGETHER
WITH
ANSWERS: -
ASSESS YOURSELF
Q1. Why are gases compressible but not
liquids?
Answer:
Gases are compressible because the
intermolecular space is very large in gases,
whereas liquids are not compressible because,
in liquids, the intermolecular space is less.
Q2. How is matter classified on the basis of
physical state?
Answer:
2. On the basis of physical properties, matter is
classified into three states of matter namely
solids, liquids, gases.
Q3. What do you think matter is made up of
small particles or not?
Answer:
Yes, Matter is made up of small particles and
these small particles are called Atoms. These
atoms are basic building blocks of all types of
matter.
Q4. Why does the level of water not change
when salt is dissolved in water?
Answer:
this happens because water molecules are not
tightly packed and have space between them
hence when we dissolve the salt in it the salt
particles occupy the space between the
3. molecules of the water. thus the water level
doesn't rise up.
Q5. What about a rubber band, can it change its
shape? Is it solid?
Answer:
Yes, a rubber band can change its shape when a
force is applied to it and can regain its shape
when the force is removed. It is solid in nature
but upon the application of force, the shape can
change due to the elastic nature of the rubber
band.
Q6. Sugar and salt kept in different jars gain the
shape of their respective jars. Are they solids?
Answer:
Sugar and salt are both solids. They take the
shape of their respective jars as the individual
crystals of each are small and many of these
4. small sugar or salt crystals can fill up the empty
spaces of a container.
Q7. What is CGS unit of volume?
Answer:
The CGS unit of volume is the litre.
How many centimetre cube are there in 1 litre?
1 litre = 1000 cubic centi meter.
Q8. What is density?
Answer:
Density of a substance is defined as the mass per
unit volume.
Q9. Why is the density of solids mostly higher
than that of liquids?
Answer:
5. The density of solids is higher than that of liquids
because the particles are more compactly
arranged in a solid with very less intermolecular
spaces between them. In liquids, these
intermolecular spaces are more and hence they
are less dense.
Q10. A sponge can be pressed easily; still it is
called a solid. Why?
Answer:
Sponge is compressible because it is having
minute pores in which air is trapped. on pressing
the air is expelled. it is still considered as a solid
because it has a definite volume and shape does
not change unless compressed.
Q11. What is kinetic energy?
Answer:
Kinetic energy is a form of energy that an object
or a particle has by reason of its motion.
6. Q12. Why do liquids flow?
Answer:
Liquids flow because the particles in a liquid are
not very tightly bound to each other and they
have high intermolecular spaces between them,
which allows the particles to be displaced or
move causing the liquids to flow.
Q13. Why do people in villages use earthen
pots in summer to cool water?
Answer:
The temperature during summer is high which
increases the rate of evaporation. Earthen pots
are made of clay that have many minute pores
in them. The pores increase the rate of
evaporation of water as the water can move via
the pores through capillary action. With the
increase in the rate of evaporation, the heat
7. energy leaves the pots in the form of kinetic
energy of the evaporated water.
This, in turn, keeps the inside of the pot cool and
the remaining water cooler. Hence, people in
villages use earthen pots in summer to cool the
water.
Q14. steam produces more severe burns as
compared to boiling water. why?
Answer:
Steam will produce more severe burns than
boiling water because steam has more heat
energy than water due to its latent heat of
vaporisation.
Q15. Temperature of a liquid does not change
when it boils. Why?
Answer:
The temperature remains constant during
boiling of water even though heat is supplied
8. constantly because all the heat energy provided
is used up in changing the state of water from
liquid to gaseous water vapour. Therefore, all
the heat energy provided to the liquid increases
the kinetic energy of the particles and
temperature doesn't increase. So supplied heat
energy is used to increase kinetic energy of
molecules.
Q16. Cotton being a solid floats on water. Why?
Answer:
Cotton is a porous solid with tiny (porous) pores
in it. Cotton's pores tend to trap air, resulting in
a lower density than water. Cotton floats on
water because cotton is lighter than water.
Cotton will begin to sink when the pores of
cotton are filled with water.
Q17. Diffusion of gases is essential in water.
Explain the term with suitable example?
9. Answer:
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.
Q18. Why people sprinkle water on the roof
after a hot sunny day?
Answer:
Evaporation causes cooling!
When water is sprinkled on the roof top or
ground it evaporates because of the latent heat
of vaporisation leaving behind a cooling effect.
in case of ground, this evaporation causes
cooling of the surrounding area after some time;
whereas in case of roof top the room beneath is
cooled.
10. Q19. Why do people perspire on a hot summer
day?
Answer:
When body temperature rises on a hot summer
day, the sweat gland starts its secretion to keep
our body temperature stable. Sweat contains
water when this water evaporates due to high
temperature it helps to cool our body.
Q20. Why a balloon kept in the sun will burst
after some time?
Answer:
The kinetic energy of gases increases with the
increase in the temperature. When the balloon
is kept in the sun, due to Sun's heat, the kinetic
energy of gaseous particles inside the balloons
also gets increased and the balloon expands.
This will increase the pressure on the walls of the
balloon. It continues to expand and comes to a
stage when the balloon bursts.
11. Q21. Why is ice at 273 K more effective in
cooling than water at the same temperature?
Answer:
Ice at 273 K will absorb heat energy or latent
heat from the medium to overcome the fusion
to become water. Hence the cooling effect of ice
is more than the water at same temperature
because water does not absorb this extra heat
from the medium.
Q22. Explain why temperature remain constant
during the change of state of any substance?
Answer:
During the change of state of any substance, the
average kinetic energy of its particles remain
constant and thus the temperature also remains
constant since it is directly proportional to the
kinetic energy of those particles.
12. Q23. Which will diffuse faster honey or ink and
why?
Answer:
The ink diffuses faster than honey because the
ink has very small particles in it and it occupies
space in between the molecules of water but
honey is more denser than water and its
Viscosity is more than water.
Q24. Convert 100 degree C to Kelvin.
Answer:
K=100+273
=373K
Q25. What are some things that sublime?
Answer:
Examples: Camphor, Iodine, Ammonium
Chloride, Naphthalene, etc.
13. Q26. Name two factors which increase the rate
of evaporation.
Answer:
Evaporation is defined as the process through
which a liquid is converted into a gas or vapor
without being heated to its boiling point. The
two main factors that affect the rate of
evaporation of a liquid are:
Temperature: The greater the
temperature of a liquid and its surroundings,
the faster the rate of evaporation.
Humidity: The greater the humidity of
the atmosphere surrounding the water, the
slower the rate of evaporation.
Q27. Why does water have higher boiling point
than alcohol? At what temperature in kelvin, it
can be change into solid state and into
vapours?
14. Answer:
Water has higher boiling point than alcohol
because the extent of hydrogen bonding is
stronger in water than in alcohol.
Moreover, we know that water freezes into ice
at 273 k and changes into vapour states at 373
K.
Q28. Among solid, liquid, and gases which one
has: -
A] maximum force of attraction between
particles.
Answer:
The force of attraction between particles of a
solid is maximum because they are closely
packed.
B] minimum force of attraction between
particles.
15. Answer:
Whereas between particles of a gas the force of
attraction is minimum due to the random
motion of the gaseous particles.
Q29. Give two reasons to justify that Water is a
liquid at room temperature.
Answer:
Water is a liquid at room temperature because
Water has a fixed volume but no fixed shape.
Water flows freely.
Q30. Evaporation is a surface phenomenon.
Explain.
Answer:
Evaporation is a surface phenomenon because it
occurs in the surface.
Example- When to put clothes for drying we
spread them out, therefore, the surface area
gets increased. When the surface area increases
16. the water will get enough space to get into
vapour stage and thus evaporation happens
easily.
Q31. Which characteristic of a gas is used in
supplying oxygen cylinders to hospitals?
Answer:
A gas is highly compressible in nature this means
that it can be compressed on applying pressure
and large volumes of gas can be stored in
cylinders and transported conveniently.
Q32. Show experimentally that matter is made
up of small particles.
Answer:
i) Take a 100ml beaker and fill it with 50ml
water. Mark the level of water in the beaker.
ii) Add 1 tablespoon of salt to it.
17. iii) Stir the water until the salt crystals can no
longer be seen and are completely dissolved.
Note the level of water.
iv) The level of water does not increase.
Explanation: The level of water does not
increase after the addition of salt. This
observation supports the assumption that
matter is made up of particles as a tablespoon of
salt contains many salt crystals which are made
up of salt crystals. These particles were able to
dissociate in water and get evenly distributed in
the intermolecular spaces present in water due
to which the level of water did not change.
18. Q33. Describe by experiment the relationship
between the rate of diffusion of liquid and
density of the liquid.
Answer:
1. Take two beakers filled with water.
2. Put a drop of blue ink slowly along the sides of
the first beaker and honey in the same way in
another beaker.
3. Leave it undisturbed.
We observe that honey diffuses slowly as
compared to ink.
rate of diffusion of liquids decreases with
increase in density of the liquid.
This experiment shows that lesser the density,
faster the rate of diffusion.
Q34. Show by an experiment that by increasing
the temperature, the substance can be
changed into liquid and then into vapours.
19. Answer:
Experiment:
i) Take a few ice cubes in a beaker and heat it
using a burner. Suspend a laboratory
thermometer into the beaker with the bulb in
contact with the ice cubes to monitor the
increase in temperature.
ii) As the temperature increases, the ice cubes
start to melt and get converted into liquid water.
iii) Upon further increase in temperature, the
water starts to boil and gets converted into
gaseous water vapour.
Explanation:
Increase in temperature causes an increase in
the kinetic energy possessed by the particles.
The increased kinetic energy starts breaking the
intermolecular forces of attraction in solid ice
and converts it into liquid water with more
intermolecular space. Further, increase in the
temperature results in a greater increase in the
kinetic energy of liquid water particles which in
20. turn get converted into their gaseous state and
evaporate.
Q35. Draw a cyclic figure to show
interconversion of states and explain fusion,
vaporisation, condensation, solidification and
sublimation.
Answer:
Fusion: The transition of a substance
from its solid state to its liquid state is known
as fusion.
Vaporisation: The transition of a liquid
into its gaseous state is known as
vaporization.
Condensation: The conversion of a gas
into its liquid state when the temperature is
lowered is known as condensation.
21. Solidification: The transition of a
substance from its liquid to its solid state is
known as solidification.
Sublimation: The direct vaporization of a
solid into its liquid state is known as
sublimation.
22. Q36. Water can be made to boil even at a
temperature below its normal boiling point.
Explain.
Answer:
The boiling of water does not only depend on
temperature. Pressure also plays a role in the
boiling of any liquid. When the pressure goes
down below the atmospheric pressure of 1 atm,
water starts to boil at a temperature lower than
its boiling temperature.
Q37. How will you determine the melting point
of ice experimentally with the help of a neat
and labelled diagram?
Answer:
Experiment:
i) Take around 10-15 ice cubes in a glass beaker
and arrange it on a tripod stand with the burner
below it.
23. ii) Suspend a thermometer in the beaker in such
a way that the bulb is in contact with the ice
cubes. A clamp stand could be used to hold the
thermometer and shown in the diagram.
iii) Switch on the flame of the burner and keep
checking the readings on the thermometer.
iv) Record the initial temperature when the ice
has just started to melt.
v) Constantly keep stirring the melting ice cubes
and record the temperature when the ice has
completely melted into liquid water.
24. Q38. How does water diffuse through their root
hair cell in plant?
Answer:
The water is transported to the other cells in the
root region by osmosis. The movements of
water is through the root hairs to the cortical
cells and then to the layer of endodermis is
through the process of osmosis down the
concentration gradient.
Q39. Why does Particles of water at 0°c have
more energy as compared to particles of ice at
the same temperature?
Answer:
This is because particles of water have the
additional latent heat which particles of ice
don’t have. So though the temperature is same
the hidden heat called as latent heat (of fusion)
25. is there in water for which the ice has got
converted into liquid. But particles of ice don’t
have this energy.
Q40. Why diffusion takes place in liquids?
Answer:
Diffusion occurs in gases like air and liquids like
water because their particles can move around
and collide with each other randomly. For
example, if you mix two drinks, the liquids
diffuse into each other.
Q41. Why does an ice cube melt when put out
of refrigerator?
Answer:
The ice cube which was solid has turned into the
liquid water because the air temperature is
warmer than the freezers. Which means the ice
particles gather heat energy from the warmer
air. Therefore, the ice particles have enough
26. energy to break apart (melt)into smaller particle
arrangements.
Q42.Shweta came back home after playing
basketball. She felt hot and sweaty. She stood
under the fan, and noticed that she started
feeling cool and dry. Explain This observation.
Answer:
Sweating is a cooling mechanism naturally
present in our body.
When our body is hot, it tries to cool itself by
releasing sweat through the pores of our skin.
The sweat thus released absorbs the excess heat
from our body and evaporates. The purpose of
the fan is to increase the rate of this
evaporation.
The fan sets the air in motion, thereby increasing
the evaporation of sweat.
Thus, the cooling sensation felt by people when
they sit under a moving fan after sweating is due
to evaporation.
27. Q43.How is melting point related to
intermolecular force of attraction? Why is the
latent heat of vaporization higher than fusion?
Answer:
On increasing the temperature of solids, the
kinetic energy of the particle increases. Due to
the increase in kinetic energy, the particles start
vibrating with greater speed and the energy
supplied by heat overcomes the forces of
attraction between the particles. The particles
leave their fixed positions and start moving
more freely. A stage is reached when the solid
melts and is converted into liquid.
Thus on increasing intermolecular force of
attraction, melting point also increases.
Because gas molecules have the biggest
intermolecular space, and the force of attraction
between them is nearly non-existent, the latent
28. heat of vaporization is larger than the latent
heat of fusion.
As a result, converting liquid to gas requires
more energy.
Hence, the latent heat of vaporization is higher
than fusion.
Q44.How will you determine the boiling point
of water experimentally? Draw a neat and
labelled diagram.
Answer:
Experiment:
i) Take around 100 ml of water in a glass beaker
and arrange bit on a tripod stand with the
burner below it.
ii) Suspend a thermometer in the beaker in such
a way that the bulb is in contact with the water.
A clamp could be used to hold the thermometer
and shown in the diagram.
iii) Switch on the flame of the burner and keep
checking the readings on the thermometer.
29. iv) Record the initial temperature when the
water is just beginning to heat up.
v) Keep monitoring the temperature change in
the thermometer while the water is heating up
further.
vi) After a while, notice the vapours coming out
of the boiling water. Record the temperature till
half of the water has evaporated.
vii) Notice that the temperature in the
thermometer will not rise above 100degree C.
Explanation:
The boiling point of water is the temperature at
which the liquid water gets converted into its
gaseous form of water vapour. The energy for
this conversion is proved in the form of heat and
is known as the latent heat of vaporisation.
As the temperature increases gradually, the
water starts heating as the kinetic energy is
increasing along with rise in the temperature.
This rise in kinetic energy keeps on increasing
the intermolecular space between the water
30. molecules and they start to move about freely.
At a certain temperature, the intermolecular
space increases up to such an extent that the
water molecules break free from each other and
vaporise. This temperature is called the boiling
point of water.
the temperature at which the water in the
beaker was seen to evaporate is 100 Degree C.
