CBSE Class 9 Science Chapter-1 Matter in our surroundings

Matter in Our Surroundings
By
N.Aarthi
B.E, M.Tech
SASTRA UNIVERSITY

Contents
• What is matter?
• Physical nature of matter.
• Characteristics of particles of matter.
• States of matter.
• Can matter change its state?
• Evaporation.
• Multiple choice questions.

What is Matter
• Air we breathe
• Food we eat
• Clouds
• Stars
• Plants and animals
• Drop of water
• Particle of sand

Physical nature of Matter
Matter is made up of particles.
Example: You mix salt/sugar in water. It spreads
throughout water.
Observation: Particles of salt/sugar fills gaps
between particles of water.

How small are these particles of
Matter?
Activity:
Step 1: Add crystals of potassium permanganate in
100ml water.
Step 2: Take 10ml of above and mix it in 90ml clear
water.
Step 3: Repeat above steps.(Dilution)
Is the water still colored?

Observation:
Few crystals can color large volumes of water.
One crystal contains millions of particles.
They keep dividing themselves into smaller
particles.

Characteristics of Particles of Matter
• Particles have space between them.
• Particles are continuously moving.
• Particles attract each other.

Particles Of Matter have space between them.
Particles of salt,sugar,dettol,potassium
permanganate got evenly distributed in water.
Conclusion: There is enough space between
particles of matter.

Particles Of Matter are continuously
moving
Activity 1:
• Put an unlit incense stick in a corner of your
class.
• How close do you have to go near it so as to
get its smell?
• Now light the incense stick. What happens?
• Do you get the smell sitting at a distance?
• Record your observations.

Solution
• One has to go very close to get the smell of the
unlit incense stick.
• After lighting the incense stick, smoke started to
coming out of it.
• Yes now, we can get smell of incense stick sitting
at a distance.
• This shows that, Matters consist of small particles
which are moving continuously. This means that
particles of matter possess kinetic energy.
• Smell of lighted incense stick diffuse with air
present in air and reaches to us sitting at a
distance.

Activity 2
• Take two glasses/beakers filled with water.
• Put a drop of blue or red ink slowly and carefully
along the sides of the first beaker and honey in
the same way in the second beaker.
• Leave them undisturbed in your house or in a
corner of the class.
• Record your observations.
• What do you observe immediately after adding
the ink drop?
• What do you observe immediately after adding a
drop of honey?
• How many hours or days does it take for the color
of ink to spread evenly throughout the water?

Solution
• Ink started mixing with water immediately after adding
which is visible in the form of many thread like
structures.
• Honey slowly directed towards bottom of water.
• It takes about one hour to spread color of ink
throughout the water.
• This happens because Ink has about equal or slightly
higher density than that of water, so ink started
immediately mixing with water, because particles of
matters are moving continuously.
• Density of honey is very high than that of water, so
honey started to direct towards bottom.
• Because particles of matters are continuously moving,
thus after some time particles of ink and water get
mixed with each other.

Activity 3
Drop a crystal of copper sulphate or potassium permanganate into a
glass of hot water and another containing cold water. Do not stir the
solution. Allow the crystals to settle at the bottom.
• What do you observe just above the solid crystal in the glass?
Solid crystals starts mixing in the water in the form of thread like
structures.
• What happens as time passes?
Coming of thread like structures in cold water is slower than that of in
the hot water.
• What does this suggest about the particles of solid and liquid?
As time passes, crystal getting dissolved in water both hot and cold.
But it takes more time to get crystal dissolved in cold water than that
of hot water.

Results-Particles are in motion.

This suggest that, matters are made up of tiny
particles and these particles are in motion
continuously.
• Does the rate of mixing change with
temperature? Why and how?
Rate of mixing increases with increase in
temperature. This is because of heat particles of
matter gets more kinetic energy and they starts
moving faster.

Particles Of Matter attract each other.
Activity 1
• Play this game in the field? make four groups and
form human chains as suggested:
• The first group should hold each other from the
back and lock arms .The second group should
hold hands to form a human chain.
• The third group should form a chain by touching
each other with only their finger tips.
• Now, the fourth group of students should run
around and try to break the three human chains
one by one into as many small groups as possible.
• Which group was the easiest to break? Why?

Solution :
The fourth group of students was the easiest to
break.
This is because students are not holding hands
or bounded even with their finger tips.
This means that there was no bonding force
present in forth group. And could be broken
easily.

Particles Of Matter attract each other.

Activity 2
• Take an iron nail, a piece of chalk and a rubber
band.
• Try breaking them by hammering, cutting or
stretching.
• In which of the above three substances do you
think the particles are held together with
greater force?
Solution
Iron nail did not break, thus its particles of iron
are held together with greater force.

Activity 3
• Open a water tap, try breaking the stream of
water with your fingers.
• Were you able to cut the stream of water?
• What could be the reason behind the stream of
water remaining together?
Solution :
• Now, we did not be able to cut the stream of
water.
• The reason behind the stream of water remaining
together is that the particles of water are held
together with force of attraction.

State of Matter
• Solid
• Liquid
• Gas

Solid state
Activity:
• Collect the following articles? a pen, a book, a
needle and a piece of wooden stick.
• Sketch the shape of the above articles in your
notebook by moving a pencil around them.
• Do all these have a definite shape, distinct
boundaries and a fixed volume?
• What happens if they are hammered, pulled or
dropped?
• Are these capable of diffusing into each other?
• Try compressing them by applying force. Are you
able to compress them?

Solution
• Yes all these have a definite shape, distinct
boundaries and a fixed volume.
• Book is torn when pulled strongly.
• Pen and piece of wooden stick are broken
when hammered.
• None is capable of diffusing into each other.
• None is compressible.

Liquid state- Activity
Collect the following:
(a) water, cooking oil, milk, juice, a cold drink.
(b) containers of different shapes. Put a 50 mL mark on these
containers using a measuring cylinder from the laboratory.
What will happen if these liquids are spilt on the floor?
Ans: All the liquids flow after spilt on the floor.
Measure 50 mL of any one liquid and transfer it into different
containers one by one. Does the volume remain the same?
Ans: Yes, volume remains same after transferring the liquid into
different containers.

Liquid gets the shape of container

Does the shape of the liquid remain the same ?
Ans: Liquid gets the shape of container.
When you pour the liquid from one container
into another, does it flow easily?
Ans: Yes all liquids flow easily.
Conclusion: Liquids have no fixed shape but has
fixed volume. It takes shape of container in
which they are kept.

Liquids are incompressible yet in industrial applications
water can be tremendously compressed and used to do
things like cut through metal.

Aquatic animals breathe under water. How?
They can breathe due to presence of dissolved
oxygen in water.
Conclusion: solids, liquids and gases can diffuse
into liquids.
Property: Rate of diffusion of liquids is higher
than that of solids. Because in liquid state,
particles move freely and have greater space
between them compared with solid state.

Gaseous state
Activity
• Take three 100 mL syringes and close their nozzles by
rubber corks.
• Remove the pistons from all the syringes.
• Leaving one syringe untouched, fill water in the second and
pieces of chalk in the third.
• Insert the pistons back into the syringes. You may apply
some Vaseline on the pistons before inserting them into the
syringes for their smooth movement.
• Now, try to compress the content by pushing the piston in
each syringe.

• What do you observe? In which case was the piston
easily pushed in?
Syringe that left untouched is pushed easily.
• What do you infer from your observations?
This shows that, there was air in syringe left untouched,
which is a gas and is compressible.
Gas is easily compressible while water (liquid) and solid
(chalk) cannot be compressed, i.e. incompressible.

Can matter change its state?
Activity: Effect of change of temperature
• Take about 150 g of ice in a beaker and suspend a laboratory thermometer so that
its bulb is in contact with the ice.
• Start heating the beaker on a low flame.
• Note the temperature when the ice starts melting.
• Note the temperature when all the ice has converted into water.
• Record your observations for this conversion of solid to liquid state.
• Now, put a glass rod in the beaker and heat while stirring till the water starts
boiling.
• Keep a careful eye on the thermometer reading till most of the water has
vaporized.
• Record your observations for the conversion of water in the liquid state to the
gaseous state.

(a) Conversion of ice to water
(b) conversion of water to water vapour

Solution
• Temperature was 0 degree Celsius when ice
starts melting.
• Temperature remained 0 degree Celsius till all
ice melted.
• Temperature starts rising after melting of ice.
• Temperature stopped rising after reaching
at 100 degree Celsius.
• Again temperature started rising after
vaporization of all water.
• This shows that supply of continuous heat while
melting of ice is used in change of phase i.e.
from solid to liquid.

• And supply of continuous heat while vaporization of
water is used in change of phase, i.e. from liquid to
vapour of water.
• Heat used in melting of ice is called Latent heat of
Fusion.
• The temperature at which a liquid starts boiling at
atmospheric pressure is known as its boiling point.
• And heat used in vaporization of water is called Latent
heat of Vaporization.

Activity
• Take some camphor or ammonium chloride. Crush it and
put it in a china dish.
• Put an inverted funnel over the china dish.
• Put a cotton plug on the stem of the funnel, as shown in
Fig. 1.7.
• Now, heat slowly and observe.
• What do you infer from the above activity?

Solution:
• After some time camphor or ammonium gets
deposited on the inner surface of funnel.
• This shows that camphor or ammonium chloride
converted directly from solid to gas and from gas
to solid.
• This process is called sublimation.
• A change of state directly from solid to gas on
heating is called sublimation.
• Direct change of gas to solid on cooling is called
deposition.

Effect of change of pressure
• Applying pressure and reducing temperature
can liquefy gases.
What is solid Co2?
It is stored under high pressure. Solid co2 gets
converted directly to gaseous state on decrease
of pressure. Solid co2 is also known as dry ice.

Evaporation
Liquid changes to vapour without reaching
boiling point
Example: water left uncovered, wet clothes dry
up.
Liquids have high kinetic energy .
So it is able to break away from forces of
attraction of other particles.
Evaporation: Phenomenon of change of liquid
into vapours at any temperature below boiling
point is called Evaporation.

Factors affecting evaporation.
• Surface area
• Temperature
• Humidity
• Wind speed.

Activity
• Take 5 mL of water in a test tube and keep it near a window or under a fan.
• Take 5 mL of water in an open china dish and keep it near a window or under a
fan.
• Take 5 mL of water in an open china dish and keep it inside a cupboard or on a
shelf in your class.
• Record the room temperature.
• Record the time or days taken for the evaporation process in the above cases.
• Repeat the above three steps of activity on a rainy day and record your
observations.
• What do you infer about the effect of temperature, surface area and wind velocity
(speed) on evaporation?

Solution
• Water kept in china dish near window evaporated
in about half an hour.
• While water kept in test tube took about one
hour to get evaporated.
• Water kept in china dish inside cupboard took
more than one hour to get evaporated.
• In rainy days, double time was taken to get water
evaporated.
• This activity shows that Rate of evaporation
increases with increase in surface area and wind
speed and decreases with increase in humidity.

How does evaporation cause cooling?
• Particles of liquid absorb energy from
surrounding to regain energy lost during
evaporation.
• This absorption of energy from surroundings
make the surrounding cold.
• Example: Nail polish remover
• It gains energy from your palm and evaporates
causing palm to feel cool.

Why should we wear cotton in
summer?
• Cotton , good absorber of water helps in
absorbing sweat and exposing it to
atmosphere for easy evaporation.

Why we notice water droplets in glass
containing ice cold water?
• Water vapour present in air on coming in
contact with cold glass of water loses energy
and gets converted to liquid state, which we
see as water droplets

Extra Questions
1. Which of the following are matter?
Chair, air, love, smell, hate, almonds, thought,
cold, lemon water, smell of perfume.
Solution: The following substances are matter:
Chair, Air, Almonds, Lemon water.

2. Give reasons for the following observation:
The smell of hot sizzling food reaches you
several meters away, but to get the smell from
cold food you have to go close.
Solution: Particles in the air, if fueled with
higher temperatures, acquire high kinetic energy
which aids them to move fast over a stretch.
Hence the smell of hot sizzling food reaches a
person even at a distance of several meters.

3. A diver is able to cut through water in a
swimming pool. Which property of matter does
this observation show?
Solution: The diver is able to easily cut through
the water in the swimming pool because of the
weak forces of attraction between water
molecules. It is this property of water that
attributes to easy diving.

4. What are the characteristics of the particles of
matter?
Solution: The characteristics of particles of
matter are:
(a) Presence of intermolecular spaces between
particles
(b) Particles are in constant motion
(c) They attract each other

5. The mass per unit volume of a substance is called
density. (density=mass/volume). Arrange the
following in the order of increasing density - air,
exhaust from the chimneys, honey, water, chalk,
cotton and iron.
Solution: The following substances are arranged in
the increasing density:
Air
Exhaust from chimney
Cotton
Water
Honey
Chalk
Iron

7. Give reasons
a) A gas fills completely the vessel in which it is
kept.
b) A gas exerts pressure on the walls of the
container.
c) A wooden table should be called a solid.
d) We can easily move our hand in the air but to
do the same through a solid block of wood we
need a karate expert

Solution:
a) Kinetic energy possessed by gas particles is very high
which allows them to randomly move across all directions
when contained, hence the particles fills the gas vessel
entirely.
b) Gas molecules possess high kinetic energy, due to
which they are under constant motion inside the
container in random directions which causes them to hit
the walls of the container and hence create vibrations.
These collisions with the walls of the container generate
pressure.
c) A wooden table should be called a solid as it possesses
all the properties of a solid such as: • Definite size and
shape • Intermolecular attraction between closely packed
particles. • It is rigid and cannot be compressed

d) Molecules in gases are loosely packed as
compared to solid molecules which are densely
packed. Hence we are easily able to break the
force of attraction when we move our hand
through air but find it difficult to break through
a solid (because of greater forces of attraction
between molecules) which a karate expert is
able to smash with the application of a lot of
force.

8. Liquids generally have a lower density than
solids. But you must have observed that ice
floats on water. Find out why?
Solution: Density of ice is less than the density
of water. The low density of ice can be
attributed to the small pores it has which allows
it to trap air hence ice floats on water.

9. Convert the following temperature to Celsius
scale:
a. 300K
b. 573K
Solution:
a. 0°C=273K
300K= (300-273)°C = 27°C
b. 573K= (573-273)°C = 300°C

10. What is the physical state of water at:
a. 250°C
b. b. 100°C ?
Solution:
(a) At 250°C - Gaseous state since it is beyond its
boiling point.
(b) (b) At 100°C - It is at the transition state as
the water is at its boiling point. Hence it
would be present in both liquid and gaseous
state

11. For any substance, why does the
temperature remain constant during the change
of state?
Solution:
It is due to the latent heat as the heat supplied
to increase the temperature of the substance is
used up to transform the state of matter of the
substance hence the temperature stays
constant.

12. Suggest a method to liquefy atmospheric
gases.
Solution: It can be achieved by either increasing
the pressure or decreasing the temperature
which ultimately leads to the reduction of
spaces between molecules.

13. Why does a desert cooler cool better on a
hot dry day?
Solution: It is because the temperature is high
and it is less humid on a hot dry day which
enables better evaporation. High levels of this
evaporation provide better cooling effects.

14. How does the water kept in an earthen pot
(matka) become cool during summer?
Solution: An earthen pot is porous in nature.
These tiny pores facilitate penetration of water
and hence their evaporation from the pot
surface. The process of evaporation requires
energy which is contributed by water in the pot
as a result of which water turns cooler.

15. Why does our palm feel cold when we put
on some acetone or petrol or perfume on it?
Solution: Acetone, petrol, and perfume are
volatile substances that get evaporated when
they come in contact with air. Evaporation is
facilitated as it uses energy from palm hence
leaving a cooling effect on our palms.

16. Why are we able to sip hot tea or milk faster
from a saucer rather than a cup?
Solution: A saucer has a larger surface area than
a cup which promotes quicker evaporation
hence the tea or milk in a saucer cools down
faster.

17. What type of clothes should we wear in
summer?
Solution: In summer, it is preferred to wear light-
colored cotton clothes because light color
reflects heat and cotton materials have pores
that absorb sweat, facilitating their evaporation
hence causing a cooling effect in the skin

Exercise
1. Convert the following temperature to Celsius
scale.
(a) 293K
(b) 470K
Solution: 0°C=273K
(a) 293K= (293 - 273)°C = 20°C
(b) 470K= (470 - 273)°C = 197°C

2. Convert the following temperatures to the
Kelvin scale.
(a) 25°C
(b) 373°C
Solution: 0°C = 273K
(a) 25°C = (25+273)K = 298K
(b) 373°C = (373+273)K = 646K

3. Give reason for the following observations:
(a) Naphthalene balls disappear with time without leaving
any solid.
(b) We can get the smell of perfume while sitting several
metres away.
Solution:
(a) At room temperature, naphthalene balls undergo
sublimation wherein they directly get converted from a solid
to a gaseous state without having to undergo the
intermediate state, i.e., the liquid state.
(b) Molecules of air move at a higher speed and have large
intermolecular spaces. Perfumes comprise of flavoured
substances that are volatile which scatters quickly in air,
becoming less concentrated over a distance. Hence we are
able to smell perfume sitting several metres away.

4. Arrange the following in increasing order of
forces of attraction between the particles -
water, sugar, oxygen.
Solution:
Oxygen (gas) < water (liquid) < sugar
(solid)

5. Give two reasons to justify -
(a) Water at room temperature is a liquid.
(b) An iron almirah is a solid at room temperature.
Solution:
(a) Transition in the states of matter of water occurs at 0°C
and 100°C. At room temperature, water is in the liquid
state, thereby exhibiting all the properties of a liquid such
as
• Water flows at this temperature
• It has a fixed volume and it takes the shape of its container
(b) The melting and boiling points of iron are as high as
1538°C and 2862°C respectively. The room temperature is
about 20-25 °C. Hence iron almirah is a solid at room
temperature.

6. Why is ice at 273K more effective in cooling
than water at the same temperature?
Solution: Water at this temperature(273K) is
less effective than ice as ice can readily form
water through absorption of ambient heat
energy as opposed to water which does not
exhibit this property as it already possesses
additional latent heat of fusion so does not
require extra heat. Hence ice cools rapidly
compared to water at the same temperature.

7. What produces more severe burns, boiling
water or steam?
Solution: Steam produces severe burns. It is
because it is an exothermic reaction that
releases high amount of heat which it had
consumed during vaporization.

Thank you
If any queries contact me
aarthisam2003@yahoo.co.in

CBSE Class 9 Science Chapter-1 Matter in our surroundings

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