Class 9 Science Notes Ch 1- Matter in Our Surroundings || Matter in Our Surroundings notes || Class 9 Chemistry Notes Matter in Our Surroundings ||

In this article we will provide you with NCERT Chapter Notes For Class 9 Science Chapter 1 Matter in Our Surroundings? to help students in their CBSE exam preparation.

These notes are according to the latest NCERT syllabus and cover points, definitions, and diagrams that are helpful for the exam.

Students can use these notes for quick revision and strengthen their board exam preparation. Written in easy language, these notes are also available for download in PDF format.

Subject	Science (Chemistry)
Class	9
Chapter No.	1
Chapter Name	Matter in Our Surroundings
Type	Notes

Science Revision Notes for CBSE Class 9 :- 

Chapter 1 :- Matter in Our Surroundings

* Matter is anything that has mass and occupies space.

--- In other words they have both mass* and volume**.

* The SI unit of mass is kilogram (kg).

** The SI unit of volume is cubic metre (m³).

--- The common unit of measuring volume is litre (L).

 

Example :        

* Consider as matter :- 

(* have mass   * occupy space)

--- All living things like plants, animals, human beings .

-- All non-living things like Solid (Table ), Liquid (water , Oil), gas (oxygen, hydrogen) .

* Not consider as matter :-

--- Abstract things like love , hatred, Respect , friendship, happiness etc. cannot be called matter. This is because they do not have mass and do not occupy space.

* As per Ancient philosophy of matter :-

-- Every living and non-living thing is made of five basic elements called the Panchtatva :- Air, Water, Earth, Sky, and Fire.

* As per Modem philosophy of Matter :-

Matter is classified on the basis of :-

o Physical Properties of Matter       

o Chemical Properties of Matter

-- Which of these is matter :- happiness, air, sandwich, thoughts, juice, and eraser?

--- Air, sandwich, juice, and eraser as they have mass, occupy space and can be broken into further particles. 

1.1 :- Physical Nature of Matter :-

1.1.1 :- Matter Is Made Up Of Particles :-

--- Is matter continuous or particulate ?

 

-- Matter is particulate in nature. This means that matter consists of particles as we can see in the microscopic image of a cube above. 

--- For Example If we put a drop of red colour in water the colour of the water turns red.

--- This happens because the particles of red colour mix with the particles of water.

Fig. 1.1 :- When we dissolve salt in water the particle of salt get into the spaces between particles of water.

-- Some of these particles mix with each other or dissolve with each other But particles in some objects cannot mix like wood and salt won't mix. 

1.1.2 What is the size of these particles ?

--- The size of the particles of matter is very small.

Activity 1.2 to show particles of matter are very small :-

Fig. 1.2 :- Estimating how small are the particles of matter. With every dilution though the colour becomes light it is still visible.

Activity 1.2 :-

--- Take 2-3 Crystals of Potassium Permanganate solution.

--- Mix it in 100 ml of water.

--- We notice water turns purple in color

--- Now, we take out 10 ml of this 100 ml and we put into 90 ml of clear water in new beaker.

--- We notice water turns purple in color

--- We again repeat this process and take out of 10 ml from this new solution and put it in another 90 ml of clear water

--- We notice that water again turns purple

--- We keep on repeating the process and water continues to turn purple

--- This experiment shows that just a few crystals of potassium permanganate can colour a large volume of water (about 1000 L). So we conclude that there must be millions of tiny particles in just one crystal of potassium permanganate, which keep on dividing themselves into smaller and smaller Particles.

1.2 Characteristics of Particles of Matter :-

1.2.1 Particles Of Matter Have Space Between Them :-

--- when we make tea, coffee or lemonade (nimbupaani ) particles of one type of matter get into the spaces between particles of the other. This shows that there is enough space between particles of matter.

Example 1 :- 

--- When we dissolve salt in water :-

Salt particles get into spaces between water particles and we are not able to see them atter they dissolve.

Example 2 :-

--- When we make tea :-

Different particles like Tea, Sugar, Milk fit into spaces between each other.

1.2.2 Particles Of Matter Are Continuously Moving-

--- From the above three activities (1.3, 1.4 and 1.5) we can conclude the following :-

--- Particles of matter are continuously moving all the time. so they possess kinetic energy.

--- As the temperature rises particles move faster. So with increase in temperature the kinetic energy of the particles also increases.

Kinetic Energy :- Energy due to motion.

--- In the above three activities we observe that particles of matter intermix on their own with each other. They do so by getting into the spaces between the particles.

--- Diffusion :- The process of mixing two different types of particles together is called diffusion.

• Diffusion becomes faster on heating.​

• In solids the particles are packed tightly, hence they vibrate about their own position.

• In liquids the particles have space to move around each other

• In gases the particles are spaced wide apart and are in constant random motion all through the space.

This movement is thus fast in gases, slower is liquids and slowest in solids.

1.2.3 Particles of Matter Attract Each Other :-

Activity 1.6 , 1.7 and 1.8

--- The above three activities (1.6, 1.7 and 1.8) suggest that particles of matter have force acting between them. This force keeps the particles together.

The strength of this force of attraction varies from one kind of matter to another.

--- The particles of matter are always held together because of a force of attraction between them.

--- The amount of this force between the particles varies in different forms of matter.

--- We can arrange the force of attraction between different types of matter (solids, liquids and gases) in increasing order as:

Gas < Liquid < Solids

Characteristics of Particles of Matter :-

--- Matter is made up of particles.

--- The particles are very small in size.

--- These particles have spaces between them.

--- These particles are constantly moving.

--- Particles attract each other.

1.3 States of Matter :-

 -- Matter is present in three different states :-

Solid state, Liquid state and Gaseous state.

1.3.1 :-  The Solid State :-

--- have a definite shape , --- Fixed volumes , --- distinct boundaries ,

--- have negligible compressibility,  --- Highly Rigid.

--- Solids may break under force but it is difficult to change their shape, so they are rigid.

---  Solid have a fixed shape and cannot be compressed. As Solids have maximum force of attraction among the particles and have no space between them.

Consider the following :-

(a) What about a rubber band can it change its shape on stretching ?Is it a solid?

--- A rubber band changes shape under force and regains the same shape when the force is removed. If excessive force is applied, it breaks.

(b) What about sugar and salt? When kept in different jars these take the shape of the jar. Are they solid?

--- The shape of each individual sugar or salt crystal remains fixed, whether we take it in our hand, put it in a plate or in a jar.

(c) What about a sponge? It is a solid yet we are able to compress it. Why?

--- A sponge has minute holes in which air is trapped when we press it the air is expelled out and we are able to compress it.

1.3.2 :- THE LIQUID STATE :-

Properties of Liquids :-

--- Fixed volumes,

--- no fixed shape,

--- compressibility,

--- Particles of Liquids are closely to each other (but not as close as solids).

--- They take up the shape of the container in which they are kept. This is because the particles of liquids have high kinetic energy they always keep on moving.

--- Liquid does not fill container completely like gases. This is because particles of liquids have higher density than gases and are close to each Other.

--- Liquids flow and change shape so they are not rigid but can be called fluid.

1.3.3 :- The Gaseous State :-

Properties of Liquids :-

--- They do not have a fixed volume. --- They do not have a fixed shape.

--- The particles of gases have the least or almost no force of attraction between them. so the particles have a large number of spaces between them.

--- Since there is a lot of space between the particles, different gases can diffuse into each other easily.

--- The kinetic energy between the particles is the maximum . Therefore the particles move around freely at high speed and there is no fixed shape of gases.

--- Due to its high compressibility, large volumes of a gas can be compressed into a small cylinder and transported easily. 

Example :- liquefied petroleum gas (LPG) , Compressed natural gas (CNG) .

* We come to know of what is being cooked in the kitchen without even entering there by the smell that reaches our nostrils. How does this smell reach us?

--- The particles of the aroma of food mix with the particles of air spread from the kitchen reach us and even farther away.

--- Due to high speed of particles and large space between them, gases show the property of diffusing very fast into other gases.

 

* Diffusion :- The process of mixing two different types of particles together is called diffusion.

--- It happens in all forms of matter - Solids, Liquids and Gases

• It is fastest in gases and slowest in solids.

• Diffusion becomes faster on heating.​

--- Diffusing solids into liquids :- Mixing sugar in tea 

--- Diffusing liquids into liquids: Mixing ink in water.

--- Diffusing gases into liquids: The presence of oxygen and carbon dioxide in Water :-

-- Aquatic Animals used dissolved oxygen in the water to breathe.

-- Aquatic plants use dissolved carbon dioxide in water for photosynthesis.

-- This is due to the diffusion of oxygen and carbon dioxide particles in water.

Examples of Diffusion in Gases :-

Eg 1 :- We take 2 gas jars, one contains brown coloured bromine gas and other containing air (which is colourless).

• Now we invert gas jar containing bromine gas over gas jar containing air.

• After some time we observe both gas jar become brown in color.

• This is because of diffusion (spreading out or mixing) bromine gas in air.

Eg 2 :- The smell of cooked food reaches our nose because of the diffusion of food gas in the air.

Eg 3 :-The smell of perfume / incense stick (agarbatti) reaches us because of diffusion of perfume gas in the air.

Examples of Diffusion of Liquids :-

Eg 1 :-  If a drop of ink is put in a jar of water, the colour soon spreads to the whole of the jar. This is due to the diffusion of ink particles in water.

Eg 2 :- If a crystal of Potassium Permanganate is put in a jar of water then whole water soon turns into a purple colour .This is due to the diffusion of potassium permanganate in water .

Examples of Diffusion in Solids :-

Diffusion in solids is slowest and takes a lot of time.

Eg 1 :- If we write something on the blackboard and do not erase it for a long period of time. The chalk panicles get diffused with particles of blackboard Hence we find it difficult to erase.

1.4 Can Matter Change its State ?

* Water exists in three states: -

Ice – solid  , 

Water – liquid  ,   

Water Vapour – Gas

--- This is an indication that matter can change its states.

Effect of Change of Temperature: -

Temperature: - Temperature is the degree of hotness or coldness of a body.

--- It refers to the degree of heat present in a matter.

--- When we add heat (thermal energy) to a substance the temperature increases.

• The kinetic energy of the particles increases and the particles vibrate faster.

• The particles thus overcome the force of attraction between each other.

• Solids ----> Liquids ----> Gas (with increase in temperature)

--- The reverse happens when a substance in cooled

• The particles come closer to each other.

• Gas ----> Liquid ----> Solid (with decrease in temperature)

What happens if we heat a solid substance ?

--- When we heat a solid substance, its temperature increases. This causes solid to melt (Convert into liquid).

Example :-

• If we take out ice from refrigerator and we keep it at room temperature.

• It melts to water (due to an increase in temperature).

--- What causes this melting of solid?

• In solids particles are closely bound together (due to high force of attraction between particles) but when we increase the temperature, the kinetic energy of particles increases.

• This causes particles to move freely and overcome the force of attraction of particles . Hence solid melts into liquid.

--- What is the Melting Point of Solids?

• The minimum temperature at which solid melts into liquids is called Melting Point of Solids.

• It indicates the strength of the force of attraction of different particles. 

Example :-

Melting Point of Ice is 273.15 K (Kelvin) or 0 ⁰ Celsius.

* How to Convert ?

0°C = 273K

Kelvin ----> Celsius ---> -273

Celsius  ----> Kelvin ---> +273

* How does Temperature of Solid Change on Applying heat?

• When we apply heat on solid.

• First its temperature keeps on increasing.

• When it reaches Melting Point, it starts convening into Liquid.

• During this period, the temperature of solid does not change.

• The temperature remains constant till the time all the solid melts into liquid due to latent heat of solid .

• After the solid melts, its temperature begins to increase again.

* What is Latent Heat?

-- Heat Energy applied to change the state of a substance (Example from solid to liquid) is called Latent Heat.

Explanation :-Normally, when we apply heat on a substance, its temperature increases .However when we apply it during its change of state (example melting of solid to liquid).

--- Its temperature does not increase during a period when the whole of solid melts .it is because heat is utilized in overcoming the force of attraction of particles of a substance. Hence it does not cause any heat .

* The word latent means hidden.

Hence latent heat means heat which is hidden in beaker and does not cause any increase in temperature.

* What are Different Types of Latent Heat ? 

--- It is of 2 types

(a) Latent Heat of Fusion   

(b) Latent Heat of Vapourization

(a) Latent Heat of Fusion :-

--- It is the amount of heat energy required to convert 1 kg of solid into a liquid state at the melting point .

Example :-

Latent heat of fusion of ice is 3.34 x 10⁵ J/kg at 0⁰ Celsius.

• It means that 3.34 x 10 ⁵ Joules of Heat is used to convert 1 kg of ice into the water at 0⁰ Celsius.

(b) Latent Heat of Vapourization :-

--- It is the amount of neat energy required to convert 1 kg of liquid into vapour at boiling point .

Example :-

--- Latent heat of Vapourization of water is 22.5 x 10 ⁵ J/kg at 100 ⁰ Celsius.

• It means that 22.5 x 10 ⁵ Joules of Heat is used to convert 1 kg of ice into water at100 ⁰ Celsius.

* What are Sublimation and Deposition?

--- Sublimation :-It means the conversion of Solids into Gas without conversion into Liquid State.

Example :- Dry ice (Solid Carbon dioxide) converts into Gas(Carbon dioxide) at room temperature.

--- Naphthalene balls disappear( change into the gaseous state) without leaving any solids.

Deposition :- It means Conversion of Gas to Solid without conversion into liquid is called Deposition.

Example :-  In Winters, Ice accumulates on Window panes (This is because Water vapour-Gas converts into ice-Solid).

Effect of Pressure to Change State of Matter :-

Pressure :-Pressure may be defined as the physical force applied on an object.

--- The particles of matter come closer to each other when pressure is applied.

--- When pressure is applied on gas enclosed in a cylinder, it is converted to liquid (as the particles come closer).

• However it is difficult to apply pressure on liquid and solids.

--- The space between the particles in solids and liquids is already very less

--- Applying pressure will not bring the particles closer and so will not bring a change in state of matter.

--- Thus, by applying pressure and cooling , gases can be converted to liquids.

--- Matter can change state because of Increase or Decrease in Pressure.

* Increase in Pressure :-

--- When pressure is applied on gas , it convert into liquid.

Example :- If we put some gas in a test tube and compress it with help of test tube it compresses (converts into liquid).

* Decrease in Pressure :-

---  Due to decrease in pressure, solid can turn into gas.

Example :-Solid Carbon dioxide (also called dry ice) gets converted into gas at room temperature .

• This is due to the decrease of pressure to 1 atm (atmosphere).

* What is 1 atmosphere?

--- The pressure of air in the atmosphere is called atmospheric pressure .The atmospheric pressure of air at sea level is taken to be 1 atmosphere

1 atmosphere = 1.01 x 10 ⁵ pascal .

* What is Evaporation :-

--- It is the  phenomenon of change of liquid into water vapours at any temperature below its boiling point is called evaporation.

Eg 1 :- When we put wet clothes on the terrace it gets dried up .This is because the water in clothes gets evaporated due to the heat rays of the sun

Eg 2 :- If we boil water, its quantity decreases after some time .This is because water in the bowl gets evaporated due to heat of flame.

* What causes Evaporation?

--- We know that liquids like water are made up of a number of molecules. All these molecules have a different level of kinetic energy in them.

• Those molecules at surface have higher level of kinetic energy move away from other molecules and. This energy is more than force of attraction binding different molecules .This causes water to get converted into water vapour and cause evaporation.

* Different Factors Affecting Evaporation

• Temperature :- As the temperature increases, the rate of evaporation also increases.

--- Clothes dry up Faster in summers rather than winters due to high temperature.

--- It is because due to higher temperature, molecules of water achieve higher kinetic energy .This makes them move away and get converted into water vapour.

• Surface area :- As the surface area increases, the rate of evaporation increases.

--- When we dry our clothes, we spread them instead of folding them .This is to increase the surface area so that more heat from the sun can reach the clothes and clothes dry faster.

• wind speed :- As the wind speed increases the rate of evaporation increases.

--- This is because due to higher winds, molecules of water obtain more kinetic energy .This makes them move away from other water molecules and evaporate faster.

• Humidity :- The rate of evaporation decreases with an increase in humidity.

--- When the level of humidity is high evaporation is low .This is because air already has such a high amount of water vapour. It is not able to hold more water vapour due to evaporation .

* Humidity is the amount of water vapour present in air.

How does Evaporation Cause Cooling? 

 

--- We know that evaporation is a process in which Liquid gets convened into gas In this process, liquid absorbs energy from surroundings .This makes surroundings cool.

Eg 1 :- On a hot day, people sprinkle water on roof .This causes the roof to cool.This is because water sprinkled gets converted into water vapour .During its process energy is used from surroundings (roof in this case) causing roof to become cool.

Eg 2 :- When we pour some acetone (nail polish remover) on our palm. We feel cool This is because when acetone evaporates (convert into vapour) .It uses heat from surroundings (palm in our case) .This causes our palm to feel cool.

Eg 3 :- Sweating help us to cool. Sweating helps to maintain our body temperature and cool us down .In summers, men we feel heat. Liquid from our body comes out as sweat .It gets evaporated (convened into water vapour).

--- Latent Heat of our body is consumed in this process of evaporation. Since heat is consumed from our body. This causes our body to cool and our body temperature is maintained.

* Why we should wear cotton clothes in summer?

--- In summers we perspire more (more sweat comes from our body). Cotton clothes are good absorber of water .They absorb water from our sweat better compared to nylon clothes .Hence they leave our body cool.

* Why do we see water droplets on outer of glass containing ice cold water.

--- Water vapour present in the air gets in contact with ice-cold water

--- It loses energy and gets convened from gaseous state to liquid state ,Thus, we see them as water droplets .