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Class 9 Science Ncert, Study notes of Chemistry

Chemistry

Ch-1 class 9 NCERT matter in our surroundings notes

Typology: Study notes

2023/2024

Available from 05/12/2025

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Std.-IX / Science / Ch- 1/ Notes / 2024-25 Page 1 of 6
ANANDA GLOBAL SCHOOL
Std. IX – Science (2024-25)
Ch- 1 Matter in our Surroundings Notes
Name: ____________________ Std / Sec: ____ Roll No. _____ Date________
In-text questions Page no. 3
1. Which of the following are matter?
Chair, air, love, smell, hate, almonds, thought, cold, cold-drink, smell of perfume.
A: Chair, air, smell, almonds, and cold-drink, smell of perfume
(Sense of smell is not matter but smell of any substance is matter)
2. Give reasons for the following observation: The smell of hot sizzling food reaches
you several metres away, but to get the smell from cold food you have to go close.
A. Kinetic energy of the particles of matter increases with increase in temperature. Rate of
diffusion in gases is very high. Hot sizzling food gives out vapours which diffuse faster in air
and thus we can smell it easily from a distance. Whereas cold food particles due to the low
kinetic energy would take a very long time to diffuse and we have to go closer to smell it.
3. A diver is able to cut through water in a swimming pool. Which property of matter does
this observation show?
A. Because of –
a) State of water in a pool is liquid
b) Presence of intermolecular space in water.
c) Intermolecular force of attraction in water or any liquid is weak hence the diver's force is
enough to overcome these forces.
4. What are the characteristics of the particles of matter?
A. a) They have intermolecular space between the constituent particles.
b) They are moving continuously and possess kinetic energy.
c) They have intermolecular force of attraction between the particles.
In-text questions Page no. 6
1. The mass per unit volume of a substance is called density.
(density = mass/volume).
Arrange the following in order of increasing density: air, exhaust from chimneys, honey,
water, chalk, cotton and iron.
A: Increasing density:
air < exhaust from chimneys < cotton < water < honey < chalk < iron.
2. (a) Tabulate the differences in the characteristics of states of matter.
(b) Comment upon the following: rigidity, compressibility, fluidity, filling a gas container,
shape, kinetic energy and density.
A: (a) Difference in the characteristics of 3 states of matter.
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ANANDA GLOBAL SCHOOL

Std. IX – Science (202 4 - 25 )

Ch- 1 Matter in our Surroundings Notes

Name: ____________________ Std / Sec: ____ Roll No. _____ Date________

In-text questions Page no. 3

1. Which of the following are matter? Chair, air, love, smell, hate, almonds, thought, cold, cold-drink, smell of perfume. A: Chair, air, smell, almonds, and cold-drink, smell of perfume (Sense of smell is not matter but smell of any substance is matter) 2. Give reasons for the following observation: The smell of hot sizzling food reaches you several metres away, but to get the smell from cold food you have to go close. A. Kinetic energy of the particles of matter increases with increase in temperature. Rate of diffusion in gases is very high. Hot sizzling food gives out vapours which diffuse faster in air and thus we can smell it easily from a distance. Whereas cold food particles due to the low kinetic energy would take a very long time to diffuse and we have to go closer to smell it. 3. A diver is able to cut through water in a swimming pool. Which property of matter does this observation show? A. Because of – a) State of water in a pool is liquid b) Presence of intermolecular space in water. c) Intermolecular force of attraction in water or any liquid is weak hence the diver's force is enough to overcome these forces. 4. What are the characteristics of the particles of matter? A. a) They have intermolecular space between the constituent particles. b) They are moving continuously and possess kinetic energy. c) They have intermolecular force of attraction between the particles. **In-text questions Page no. 6

  1. The mass per unit volume of a substance is called density. (density = mass/volume). Arrange the following in order of increasing density: air, exhaust from chimneys, honey, water, chalk, cotton and iron. A:** Increasing density: air < exhaust from chimneys < cotton < water < honey < chalk < iron. 2. (a) Tabulate the differences in the characteristics of states of matter. (b) Comment upon the following: rigidity, compressibility, fluidity, filling a gas container, shape, kinetic energy and density. A: (a) Difference in the characteristics of 3 states of matter.

A2 (b). Rigidity- It is the property of matter to resist the change in its shape. Compressibility - It is the property of matter in which its volume is decreased by applying force. Fluidity- It is the ability of matter to flow. Filling a gas container - On filling a gas, it takes the shape of the container and the individual particles being far away fill up the entire container. Shape- Having definite boundaries Kinetic energy- It is the energy possessed by the particles of matter due to its motion. Density- It is the ratio of mass per unit volume.

3. 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 air but to do the same through a solid block of wood we need a karate expert. A. a) Gases have the least/negligible intermolecular force of attraction and very high kinetic energy. As a result these particles move / flow randomly in all directions, so they fill up the vessel completely in which they are kept. b) Gases have very high kinetic energy. Hence gases have random motion in all directions. So, freely moving particles of gas hit the walls of the container continuously and this exerts pressure on the walls of the container.

CHARACTERISTICS SOLIDS LIQUIDS GASES

Arrangement of Molecules Particles are tightly/ closely packed Particles are loosely packed Particles are far apart/ separated from each other by wide spaces Inter molecular force of attraction Very high/ Maximum Less as compared to solids Very less/ Least/ Minimum Intermolecular space Very less/ Least/ Minimum More than solids, less than gases Very high/ Maximum Vibration of particles Particles vibrate at their mean position Particles can move within their boundary Particles can move randomly Shape Have a definite shape Do not have definite shape. They take the shape of the container No definite shape Volume Have definite volume Have definite volume No definite volume Boundaries Have distinct boundaries Have distinct boundaries No distinct boundaries Hardness/ Rigidity Very hard and rigid Not hard and rigid Not hard and rigid Fluidity Do not flow Flow in a particular direction (high to low) Flow randomly in all directions Compressibility Not compressible Not compressible Highly compressible Density Generally high density Generally low density Generally very low density Rate of Diffusion Very low More than solids, less than gases Very high Storage Can be stored without a vessel Cannot be stored without a vessel Can be stored in a closed vessel only Kinetic energy Least Intermediate Very large/very high Expansion on Heating Very low/ less Intermediate High capacity to expand on heating

In-text questions Page no. 12

1. Convert the following temperatures to the Celsius scale. (a) 293 K (b) 470 K. A: (a) 293 K into °C 293 – 273 = 20°C (b) 470 K into °C 470 – 273 = 197°C 2. Convert the following temperatures to the Kelvin scale. (a) 25°C (b) 373°C. A: (a) 25°C into K 25 + 273 = 298 K (b) 373°C into K 373 + 273 = 646 K 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 sitting several metres away. A. (a) Naphthalene balls undergo sublimation at room temperature due to which it converts directly into vapour state (gas) from solid state without leaving any residue. (b) When sprayed, vapours from the perfume diffuse in air very fast at room temperature. So we can smell them, sitting several metres away. The diffusion of perfume is possible due to the presence of large empty spaces between air particles. 4. Arrange the following substances in increasing order of forces of attraction between the particles—water, sugar, oxygen. A. Oxygen —> water —> sugar 5. What is the physical state of water at— (a) 25°C (b) 0°C (c) 100°C A. (a) 25°C is liquid (b) 0°C is solid or liquid (c) 100°C is liquid and gas 6. Give two reasons to justify: (a) water at room temperature is a liquid. (b) an iron almirah is a solid at room temperature. A. (a) Water at room temperature is a liquid because its freezing point is 0°C and boiling point is 100°C. (b) An iron almirah is a solid at room temperature because melting point of iron is higher than room temperature. At this temperature, iron has a definite shape and volume. It is hard and rigid. 7.Why is ice at 273 K more effective in cooling than water at the same temperature? A. Water at 273K or 0OC has absorbed heat energy equal to the latent heat of fusion from the surroundings. Whereas ice at the same temperature has not absorbed heat. Hence, ice is more effective in cooling than water at the same temperature. 8. What produces more severe bums, boiling water or steam? A. Steam at 373K or 100OC has absorbed heat energy equal to the latent heat of vapourization. Whereas water at the same temperature has not absorbed heat. Hence, steam produces more severe burns than boiling water. 9. Name A, B, C, D, E and F in the following diagram showing change in its state A. A —> Liquefication/melting B —> Vapourisation /evaporation C—>Condensation D—> Solidification E —> Sublimation F —> Deposition/Desublimation

Note book work: LATENT HEAT (Why does temperature remain constant while melting/boiling?) Latent heat is the heat supplied to overcome the forces of attraction between the particles of the substance during the change of state. Energy must be supplied to a substance to melt it or to boil it, i.e. to change its state. This energy does not increase the temperature of the substance. It does not increase the kinetic energy of the particles of the substance so the temperature does not rise. This heat utilized in changing the state of the substance is called latent heat. Latent heat of fusion- The amount of heat required to convert 1 kg of a substance from the solid state to liquid state at 1 atmosphere pressure and at its melting point without any change in temperature. The latent heat of fusion of ice is 336 joules/gram. Latent heat of vapourization- The amount of heat required to convert 1 kg of a substance from the liquid state to gaseous state at 1 atmosphere pressure and at its boiling point without any change in temperature. The latent heat of vapourization of water is 2260 joules/gram. 1 calorie = 4.186 joules. MELTING- The process of change from solid state to liquid state at a particular temperature. BOILING- The process of change from liquid state to gaseous state at a particular temperature. MELTING POINT- The temperature at which a solid melts to become a liquid at 1 atmosphere pressure. BOILING POINT- The temperature at which a liquid starts changing into gas at 1 atmosphere pressure. SUBLIMATION- The process in which a substance changes directly from solid state to gaseous state, without passing through the intermediate liquid state. E.g. Dry ice (solid CO 2 ), Iodine, naphthalene, camphor etc. DESUBLIMATION- Desublimation is the reverse process of sublimation. The process in which a substance changes directly from the gas to the solid state, with no intermediate liquid state. When these solids are heated their particles move so quickly that they separate completely to form vapour. When these vapours are cooled, these particles slow down so quickly that they become fixed and form a solid. EFFECT OF CHANGE OF PRESSURE ON STATES OF MATTER When a gas is compressed, the particles will come closer to each other and inter molecular force of attraction increases. As a result the gas changes into liquid state. E.g. Butane gas (a component of petroleum) is compressed so as to change into liquid state and filled in cooking gas cylinders as L.P.G. (Liquefied Petroleum Gas) E.g. Gaseous CO 2 changes into solid CO 2 when temperature is reduced to about - 78.4OC and pressure is 1 atmosphere. Solid CO 2 is called dry ice as it resembles ice and used for cooling but does not turn into liquid state and wet the surface. Dry ice (solid CO 2 ) undergoes sublimation and changes into gaseous state above −78.4 °C and at 1 atmosphere pressure. ANOMALOUS EXPANSION OF WATER Density of water changes with temperature in a unique way. Normally in other liquids, volume of liquid decreases on cooling (volume decreases as temperature decreases), so density of the liquid increases. But when water is cooled it first contracts upto 4OC i.e. its volume decreases with decrease in temperature. And when we further reduce the temperature from 4 OC to 0 OC, it starts expanding instead of contracting and continues to expand till it reaches 0 OC, where it freezes into