Matter in Our Surroundings Class 9 Science Notes

Please refer to Matter in Our Surroundings Class 9 Science Notes and important questions below. The Class 9 Science Chapter wise notes have been prepared based on the latest syllabus issued for the current academic year by CBSE. Students should revise these notes and go through important Class 9 Science examination questions given below to obtain better marks in exams

Matter in Our Surroundings Class 9 Science Notes and Questions

The below Class 9 Matter in Our Surroundings notes have been designed by expert Science teachers. These will help you a lot to understand all the important topics given in your NCERT Class 9 Science textbook.

Refer to Chapter 1 Matter in Our Surroundings Notes below which have been designed as per the latest syllabus issued by CBSE and will be very useful for upcoming examinations to help clear your concepts and get better marks in examinations.

Revision Notes for Class 9 Science Chapter 1 Matter in Our Surroundings

• Anything that occupies space and has mass and is felt by senses is called matter.
• According to indian ancient philosopher, matter is the form of five basic elements (the Panchtatva) – air , earth ,fire , sky and water.

Characteristics of particles of matter

Made of tiny particles.
Vacant spaces exist between particles.
Particles are in continuous motion.
Particles are held together by forces of attraction.

States of Matter
Basis of Classification of Types

Based upon particle arrangement
Based upon energy of particles
Based upon distance between particles

Five states of matter

Solid
Liquid
Gas
Plasma
Bose-Einstein condensate

(I) SOLID

Important Questions Class 9 Science Chapter 1 Matter in Our Surroundings

Fixed mass, volume and shape
Inter-particle are least.
Incompressible distances.
High density and do not diffuse
Inter particle forces of attraction are strongest.
Constituent particles are very closely packed.

(II) LIQUID

Not fixed shape but fixed volume and mass.
Inter particle distances are larger than solid.
Almost incompressible.
Density is lower than solids and can diffuse.
Inter particle forces of attraction are weaker than solids .
Constituent particles are less closely packed.

(III) GAS

Neither fixed shape nor fixed volume.
Inter particle distances are largest.
Highly compressible.
Density is least and diffuse.
Inter particle forces of attraction are weakest.
Constituent particles are free to move about.

(IV) PLASMA (NON-EVALUATIVE)

A plasma is an ionized gas.
A plasma is a very good conductor of electricity and is affected by magnetic fields.
Plasma, like gases have an indefinite shape and an indefinite volume. Ex. Ionized gas

(v) BOSE-EINSTEIN CONDENSATE (non –evaluative)

A BEC is a state of matter that can arise at very low temperatures.
The scientists who worked with the Bose-Einstein condensate received a Nobel Prize for their work in 1995.
The BEC is all about molecules that are really close to each other (even closer than atoms in a solid).

Microscopic Explanation for Properties of Solids

Solids have a definite shape and a definite volume because the particles are locked into place
Solids do not flow easily because the particles cannot move/slide past one another
Solids are not easily compressible because there is little free space between particles

Microscopic Explanation for Properties of Liquids

Liquids are not easily compressible and have a definite volume because there is little free space between particles.
Liquids flow easily because the particles can move/slide past one another.
Liquids flow easily because the particles can move/slide past one another.

Microscopic Explanation for Properties of Gases

Gases are easily compressible because there is a great deal of free space between particles
Gases flow very easily because the particles randomly move past one another.
Gases have an indefinite shape and an indefinite volume because the particles can move past one another (non –evaluative)

Microscopic Explanation for Properties of Plasmas

Plasmas have an indefinite shape and an indefinite volume because the particles can move past one another.
Plasmas are easily compressible because there is a great deal of free space between particles.
Plasmas are good conductors of electricity &are affected by magnetic fields because they are composed of lens.

Microscopic Explanation for Properties of BEC

Particles are less energetic than solids because Exist at very low temperature.
Particles are literally indistinguishable because they are locked into same space .
BEC shows super fluidity because Particles can flow without friction.

1. Interchange in states of matter

Water can exist in three states of matter –

Solid, as ice,
Liquid, as the familiar water, and
Gas, as water vapour.

Sublimation : The changing of solid directly into vapours on heating & vapours into solid on cooling. Ex. Ammonium chloride, camphor & iodine.

(a) Effect of change in temperature

The temperature effect on heating a solid varies depending on the nature of the solid & the conditions required in bringing the change.

On increasing the temperature of solids, the kinetic energy of the particles increases which overcomes the forces of attraction between the particles thereby solid melts and is converted to a liquid.
The temperature at which a solid melts to become a liquid at the atmospheric pressure is called its melting point.
The melting point of ice is 273.16 K.
The process of melting, that is, change of solid state into liquid state is also known as fusion.

(b) Effect of Change of Pressure

Increasing or decreasing the pressure can change the state of matter. Applying pressure and reducing temperature can liquefy gases.
Solid carbon dioxide (CO₂CO₂) is stored under high pressure. Solid CO₂CO₂ gets converted directly to gaseous state on decrease of pressure to 1 atmosphere without coming into liquid state. This is the reason that solid carbon dioxide is also known as dry ice.

Latent Heat :

The hidden heat which breaks the force of attraction between the molecules during change of state.
Fusion Heat energy required to change 1kg of solid into liquid.
Vaporisation Heat energy required to change 1kg of liquid to gas at atmospheric pressure at its boiling point
Thus, we can say that pressure and temperature determine the state of a substance, whether it will be solid, liquid or gas.

4. Evaporation & Boiling

Particles of matter are always moving and are never at rest.
At a given temperature in any gas, liquid or solid, there are particles with different amounts of kinetic energy.
In the case of liquids, a small fraction of particles at the surface, having higher kinetic energy, is able to break away from the forces of attraction of other particles and gets converted into vapour .
This phenomenon of change of a liquid into vapours at any temperature below its boiling point is called evaporation.

Factors Affecting Evaporation

The rate of evaporation increases with an increase of surface area.
With the increase of temperature, more number of particles get enough kinetic energy to go into the vapour state.
Humidity is the amount of water vapour present in air. The air around us cannot hold more than a definite amount of water vapour at a given temperature. If the amount of water in air is already high, the rate of evaporation decreases.
Wind speed : the higher the wind speed , the more evaporation.

Evaporation cause cooling.

The particles of liquid absorb energy from the surrounding to regain the energy lost during evaporation,

Evaporation Vs Boiling

Boiling is a bulk phenomenon. Particles from the bulk (whole) of the liquid change into vapour state.
Evaporation is a surface phenomenon. Particles from the surface gain enough energy to overcome the forces of attraction present in the liquid and change into the vapour state.

5. Kelvin & Celsius Scale

Kelvin is the SI unit of temperature, 0∘C0∘C = 273.16 K we take 0∘C0∘C = 273 K.
SI unit of temperature is Kelvin. T(K)=T(0C)+273T(K)=T(0C)+273
Kelvin scale of temperature has always positive sign , hence regarded as better scale than Celsius.
Atmosphere (atm) is a unit of measuring pressure exerted by a gas. The SI unit of pressure is Pascal (Pa):
1 atmosphere = 1.01 × (10 to the power 5) Pa. The pressure of air in atmosphere is called atmospheric pressure. The atmospheric pressure at sea level is 1 atmosphere, and is taken as the normal atmospheric pressure.

You are expected to know

Particle nature of matter.
All five states of matter & their behaviour
enter conversion of states of matter
Latent heat
Conversion between Kelvin scale & Celsius scale

Questions for Class 9 Science Chapter 1 Matter in Our Surroundings

Question What is humidity?
Ans : The air holds water vapour, this air with water is called humid air and the amount of water vapour present in the air is called humidity.

Question Name the state of water at 100 degree Celsius, zero degree Celsius and 4 degree Celsius.
Ans : The state of water at 100 degree Celsius is gas, at 0 degree Celsius it is solid and at 4 degree Celsius it is liquid.

Question Is it possible to turn a liquid into vapour without heating?
Ans : Yes, by the process of evaporation as evaporization of water occur below the boiling point under atmospheric pressure.

Question Why is water liquid at room temperature?
Ans : At room temperature, the molecules of water have some intermolecular force of attraction and the room temperature cannot provide sufficient heat for these molecules to overcome their force of attraction and therefore, remain in liquid phase.

Question Cotton is solid but it floats on water. Why?
Ans : Cotton has large number of pores where air is trapped. This process reduces cotton’s density and increase the volume. Therefore, cotton floats on water. But, when these pores get filled with water, it starts sinking.

Question What is normal atmospheric pressure?
Ans : The atmospheric pressure at sea level is 1 atmosphere and taken as the normal atmospheric pressure.

Question Give two examples of diffusion.
Ans : Milk drops dissolved in water and perfume sprayed in a room.

Question On a hot sunny day, why do people sprinkle water on the roof or open grounds?
Ans : During hot sunny day, the surface of roof or ground absorbs large amount of heat and remains hot. On sprinkling water on these surfaces, the water absorbs large amount of heat from the surface of roof and water evaporates thereby causing cooling effect.

Question Discuss the factors which affect evaporation.
Ans : There are four factors which affect evaporation.
(i) Surface area : Escaping of particles from liquid state to vapour state depends on surface area.
Therefore, the rate of evaporation increases with surface area.
(ii) Temperature : Rise in temperature, rise the kinetic energy of substance and therefore, chance of escaping of particles is great from liquid to vapour state.
(iii) Wind : The rate of evaporation increases with speed of wind.
(iv) Humidity : Humidity is the amount of vapour present in the air. At fixed temperature air can’t hold more than fixed amount of water vapour.
Therefore, the evaporation rate decreases if humidity increases in air.

Question. What is the significance of boiling point and melting point of a substance?
Ans : The significance of boiling point and melting point is that it shows the purity of the substance.

Question When we put CuSO4 in water, after some time we find the solution turns blue. Why? Also, on heating it, what change will occur?
Ans : The solution turns blue because of diffusion. On heating the solution, nothing will happen.

Question Give the temperature at which water exists in two different phases/states.
Ans : (i) At 0°C water can be in solid or in liquid state.
(ii) At 100°C water can be in liquid or in gaseous state.

Question The melting point of ice is 273.16 K. What does this mean? Explain in detail.
Ans : Ice is solid at 0°C, i.e. 273 K. The molecules of ice are tightly packed. These molecules have to overcome the force of attraction with which they are held and hence, they gain this heat from the surrounding but the temperature remains the same as their energy is used to overcome the force of attraction between the particles. The particles of ice start vibrating freely and a stage reaches when the solid ice melts and is converted to liquid state at the same temperature,
i.e. 273 K.

Question How can you justify that table is a solid?
Ans : When we apply force on the table it doesn’t change its shape because its inter- molecules are tightly packed, this shows that table is solid.

Question The boiling point of alcohol is 78°C. What is this temperature on Kelvin scale?
Ans : K = °C + 273 = 78 + 273 = 351 K

Question Why are light and sound not considered as matter?
Ans : Light and sound are not considered as matter because they have no mass and do not occupy space.

Question The Kelvin scale temperature is 0 K. What is the corresponding Celsius scale temperature?
Ans : –273°C

Question. How is the high compressibility property of gas useful to us?
Ans : The gases have high compressibility. This property is used in the following situation :
(i) LPG (Liquefied Petroleum Gas) is a fuel which is made up of petroleum gas. On compressing this petroleum gas it forms liquid.
(ii) Oxygen cylinders in the hospitals have compressed gas filled in it.
(iii) CNG (Compressed Natural Gas) is a natural gas i.e. methane, which is compressed and used as a fuel in vehicles and at home.

Question With the help of an example, explain how diffusion of gases in water is essential?
Ans : The gases from the atmosphere diffuse and dissolve in water. Diffused gases like oxygen and carbon dioxide 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.

Question Is it true to say that fluorescent tube contains plasma? Explain
Ans : It is right to say that fluorescent tube contains plasma. As fluorescent tube has helium or some other rare gas. The particles of the gas get ionized in the presence of high voltage applied. These charged particles are called plasma which glows.

Question A rubber band is a solid, but it can change its shape. Why?
Ans : A rubber band changes shape under force and regains the shape when the force is removed, this is due to less intermolecular force of attraction between the particles.

Question. We can get the smell of perfume sitting several metres away, why?
Ans : This is because perfumes diffuse very fast and can reach to people sitting several metres away.

Question When salt or sugar is poured into different kinds of vessels, why do they take the shape of vessel as they are solid?
Ans : Salt or sugar takes the shape of containing vessel, but does not change its individual shape. For example : Sugar crystal is cubical and they remain cubical in any vessel.

Question. What is dry ice?
Ans : Solid carbon dioxide obtained by cooling and applying pressure on carbon dioxide gas. It does not melt so it is called dry ice.

Question What are fluids?
Ans : The states of matter that can flow due to less intermolecular force of attraction are liquids and gases and are called fluids.

Question Sponge is a solid, yet we are able to compress it. Why?
Ans : Sponge has very small holes throughout its structure. These holes are filled with air. When it is compressed, the air in the holes is squeezed out. Thus, we are able to compress it.

Question What is the difference between a gas and plasma?
Ans : (i) Gas consist neutral particles which are associated with energies comparable with atmospheric temperature.
(ii) Plasma contains energetic particles in the form of ionized gases.

Question. Why do we see water droplets on the outer surface of a glass containing ice-cold water?
Ans : If we take some ice-cold water in a glass, after some time we will see small droplets of water deposited on the outer walls of the glass. Because water vapour present in air come into the contact of cold wall ofglass, lose energy and converted into liquid statehich can be seen in the form of small droplets.

Question 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. Why?
Ans : In air, the inter-particle attractive forces are negligible and hence, it is easy to separate the particles in air and we can easily move our hand in air. The interparticle forces are very strong in solids. So, it is not easy to separate the particles and it is not easy to move our hand through a solid block of wood.

Question. A piece of chalk can be broken into small pieces whenhammered but it is not possible in case of iron bar. Why?
Ans :The force that keeps the particles together is lesserin chalk; hence it could be easily broken down into pieces on hammering. Whereas, the magnitude of this intermolecular force is more in iron, hence it cannot be broken into small pieces on hammering.

Question. Explain, why solids have fixed shape but liquids and gases do not have fixed shape?
Ans : Solids have fixed shape due to strong intermolecular force of attraction between them. The liquids and gases have molecules with less intermolecular force of attraction, and hence they can flow and take shape of the container.

Question What is diffusion?
Ans : The intermingling of molecules of one substance with that of the other is called diffusion.

Question What happens to the rate of diffusion if the temperature is increased?
Ans : With increased temperature, the rate of diffusion also increases as the particles gain energy and vibrate more.

Question Liquids and gases can be compressed but it is difficult to compress solids. Why?
Ans : Liquids and gases have intermolecular space; on applying pressure externally on them the molecules can come closer thereby minimizing the space between them. But in case of solids, there is no intermolecular space to do so.

Question A balloon when kept in Sun, bursts after some time. Why?
Ans : The balloon has air filled in it. The balloon when kept in Sun gets heated and the air inside it also gets heated. The molecules of air get energy, and vibrate faster thereby exerting large force on the walls of the balloon. Due to this expansion of gases the balloon bursts.

Question Define melting point.
Ans : The temperature at which a solid melts to become liquid at the atmospheric pressure is called its melting point.

Question. Define matter.
Ans : Anything that occupies space and has mass and is felt by senses is called matter.

Question Why do people perspire a lot on a hot humid day?
Ans : On a hot humid day, due to the heat our body starts sweating and gives cooling effect by evaporation. But the air cannot hold any more water on a humid day and therefore, the sweat or perspiration is seen.

Question Why is it advisable to use pressure cooker at higher altitudes?
Ans : At higher altitudes, the atmosphere pressure is low and the water boils very fast and evaporates at faster rate, therefore, the pressure is required to increase the cooking process and this is done by using pressure cooker which increases the pressure inside the container and cooks food faster.

Question What happens if you put copper sulphate crystals in water?
Ans : Copper sulphate crystals mixed between the spaces of molecules of water and disappear.

Question Give state of a matter if this substance has neither a fixed shape nor a fixed volume.
Ans : Gas.

Question Why cannot you smell its perfume at a short distance when incense stick is not lighted?
Ans : The particles of the perfume (matter) do not have sufficient energy to drift through the air. Thus, we cannot smell it at a few steps away from incense stick.

Question Why a rubber band is considered as a solid?
Ans : We can regard rubber band as a solid, because it regains its shape when the stretching force is removed from it.

Question. Predict the physical state of melting point of a substance is below the room temperature.
Ans : Ice.

Question. What do you mean by vapour?
Ans : A substance that is found in gaseous state only at room temperature is called vapour.

Question Why is the smell of the perfume of incense stick filled the whole room in few minutes, when lighted?
Ans : When the incense stick is lighted, the heat energy makes the particles of the perfume to move rapidly.
Thus, they easily drift through the air in the room and hence, we can smell it anywhere in the room.

Question What do you observe when force is applied and then removed on the plunger of the syringe containing air? Give a reason for your answer.
Ans : The plunger moves downward on the application of force to a considerable length. The plunger move backward and takes its original position when the force is removed.
The gases have large intermolecular spaces. So, they easily get compressed on the application of force.
The compressed gases are under high pressure. When the force is removed, this high pressure forces the plunger back to its original position.

Question State the effect of pressure on boiling point.
Ans : Boiling point increases with increase in pressure.

Question. Name any two substances which sublime.
Ans : Camphor and naphthalene.

Question Define condensation.
Ans : The change of solid state from liquid state on cooling

Question Which is the slow process, evaporation or boiling?
Ans : Evaporation.

Question. What is the effect of surface area on rate of evaporation?
Ans : If the surface area is increased, the rate of evaporation increases.

Question A karate expert can easily move his hand through a solid block of wood but we cannot. Why?
Ans : In a solid block of wood, the inter-particle forces are very strong and hence, it is not easy to separate the particles. Therefore, it is not easy to move our hand through a solid block of wood, only a karate expert can do it as he has expertise in this.

Question What is latent heat of fusion?
Ans : The heat required to change 1 kg of a solid substance into liquid state at the melting point of the substance.
For example : Amount of heat required to melt ice at 0°C into water, at 0°C will be known as the latent heat of fusion of ice.

Question Write the SI unit of temperature?
Ans : Kelvin.

Question. Why is Kelvin scale of temperature regarded as better scale than Celsius?
Ans : As it has wide range of measurement and Kelvin scale of temperature has always positive sign, hence regarded as better scale than Celsius. Kelvin is an absolute thermodynamics scale, which uses its null point as the temperature at which all thermal motion ceases to exist.

Question. What is compressibility? How it is negligible in solids?
Ans : Compressibility is the ability of a substance to be reduced to its volume under pressure. Solids are incompressible as their particles are held together. So, we can tell that compressibility is negligible in solids.

Question. Two cubes of ice are pressed hard between two palms and after releasing the pressure, the cubes join together. Why?
Ans : Pressure is directly proportional to temperature when we apply pressure, temperature increases then the ice in contact melts and it turns into water. When pressure is removed, the temperature decreases again and melted ice again freezes. Hence, cubes join together.
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Question Convert 10°C into Kelvin scale.
Ans : 273 + 10 = 283 K

Question. Does solid ice and liquid water co-exist together? If yes, then at what temperature?
Ans : At 0°C, the three phases of water co-exist called triple point.

Question What is the reason that “Ice has lower density than water”?
Ans : The mass per unit volume of a substance is called density (density = mass/volume). The density of substance decreases as the volume of a substance increases. Space between particles increases when water changes into ice. These spaces are larger as compared to the spaces present between the particles of water. Thus, the volume of ice become greater
as compared to the water. Hence, the density of ice ecome lower than that of water. And, a substance with lower density than water can float on water. Thus, ice floats on water.

Question. Why does the temperature remain constant during the change of state, for any substance?
Ans : On increasing the temperature of solids, the kinetic energy of the particles increases which is used up in changing the state as it overcome the forces of attraction between the particles, therefore, the temperature remains constant during the change of state.

Question What is common among the three states of matter?
Ans : They all contain molecules.

Question. Which property of gas is used in supplying oxygen cylinders to hospitals?
Ans : Compressibility.

Question. Both the process of evaporation and boiling involves he change of state from liquid to gas but still they are different from each other. Justify.
Ans : Evaporation is different from boiling as evaporation is a natural phenomenon, occurs on the surface of the water and also it is a slow process, whereas boiling is an artificial phenomenon, it occurs in the bulk of the liquid and is a fast process.

Question. How can you show that evaporation causes cooling?
Ans : When we put some acetone on our hand, after some time we will feel coolness on our hand because the acetone absorbs kinetic energy from our hand and evaporates and evaporation causes cooling.

Question A substance x is highly compressible and could easilybe liquefied. It can also take the shape of the container.
Guess the nature of the substance.
Ans : Gas.

Question What is plasma?
Ans : Plasma is a state of matter consisting of super excited particles of very high energy level.

Question. Express the boiling point of water in Celsius as well as Kelvin scale.
Ans : 100°C and 373 K.

Question. What do you mean by latent heat of vaporization?
Ans : The latent heat of vaporization of a liquid is the quantity of heat in joules required to convert 1 kilogram of the liquid to vapour or gas at its boiling point, without any change in temperature.

Question. What property of gas is used when natural gas is supplied for vehicles?
Ans : A gas is highly compressible and a large quantity of it can be compressed to a small, manageable volume. Thus, natural gas is compressed and is supplied for use by vehicles in the name of CNG (compressed natural gas).

Question. How is pressure developed in a container full of a gas?
Ans : The gaseous particles are free to move in the container. These move at high speed and collide with other particles of the container. The bombardment of the particles on the walls of the container produces a steady force that depends on the temperature. This force per unit area is called as pressure of the gas.

Question. Why evaporation is called surface phenomenon?
Ans : Evaporation is called surface phenomenon as evaporation occur on the surface of liquid.

Question Name two processes from which it may be concluded that the particles of a gas move continuously.
Ans : Compressibility and Brownian movement.

Question Is it not proper to regard the gaseous state of ammonia as vapours? Explain.
Ans :The gaseous state of a substance can be regarded as vapours only in case it is a liquid at room temperature.
Since ammonia is a gas at room temperature, its gaseous state cannot be regarded as vapours. Naphthalene is volatile solid and has a tendency to sublime. So, it changes into vapours completely, thus disappear into the air and no solid is left.

Question. State characteristics of matter demonstrated by :
(i) Diffusion.
(ii) Brownian motion.
Ans : (i) Diffusion involves movement of different particles so that they become intermixed uniformly.
(ii) Brownian motion : It is the zig-zag movement of the small particles suspended in a liquid or a gas.