Class 9 NCERT Important Questions and Answers
Science Chapter 1 - Matter in our surroundings

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NCERT Class 9 Science - Important Questions and Answers
Chapter 1- Matter in our surroundings

Introduction

1. What is everything in the universe made up of?
   Answer: Everything in the universe is made up of material which scientists have named "matter".
   
   
2. What are the five basic elements of matter according to early Indian philosophers?
   Answer: The five basic elements of matter according to early Indian philosophers are air, earth, fire, sky, and water.
   
   
3. What are the two types of classification of matter done by modern-day scientists?
   Answer: The two types of classification of matter done by modern-day scientists are based on their physical properties and chemical nature.
   
   
4. What is the purpose of the activity described in 1.1.1?
   Answer: The purpose of the activity is to decide about the nature of matter — whether it is continuous or particulate.
   
   
5. What happens to the level of water in the beaker after dissolving salt/sugar in it?
   Answer: The level of water remains unchanged.
   
   
6. What do we conclude from the experiment in activity 1.1.2 with potassium permanganate?
   Answer: The experiment shows that just a few crystals of potassium permanganate can color a large volume of water, indicating the presence of millions of tiny particles in just one crystal of potassium permanganate.
   
   

Short Answer type questions

1. What is the universe made up of?
   Answer: The universe is made up of material called "matter." Matter includes everything we see around us, such as the air we breathe, the food we eat, stones, clouds, stars, plants, animals, water droplets, and particles of sand.
   
   
2. What are the characteristics of matter in the universe?
   Answer: All things in the universe, living or non-living, have mass and volume. They occupy space and have a certain amount of material or substance in them.
   
   
3. How did early Indian philosophers classify matter?
   Answer: Early Indian philosophers classified matter into five basic elements known as the "Panch Tatva." These elements were air, earth, fire, sky, and water, and they believed that everything in the universe was made up of these elements.
   
   
4. What did ancient Greek philosophers believe about matter?
   Answer: Ancient Greek philosophers had a similar classification of matter as the early Indian philosophers. They also believed that matter was composed of different elements.
   
   
5. How have modern-day scientists classified matter?
   Answer: Modern-day scientists have evolved two types of classification of matter based on their physical properties and chemical nature. However, in this chapter, we will focus on matter's classification based on its physical properties, and the chemical aspects of matter will be discussed in later chapters.
   
   
6. Describe the activity "1.1" briefly.
   Answer: In the activity, a 100 mL beaker is taken, half-filled with water, and the water level is marked. Then, some salt or sugar is dissolved in the water using a glass rod. Observations are made regarding any change in the water level, what happens to the salt/sugar, and whether the level of water changes.
   
   
7. What conclusion can be drawn from activity "1.1"?
   Answer: The conclusion from activity "1.1" is that matter is made up of particles. When salt or sugar is dissolved in water, it spreads throughout the water, indicating the particulate nature of matter.
   
   
8. Describe the activity "1.2" briefly.
   Answer: In activity "1.2," 2–3 crystals of potassium permanganate are dissolved in 100 mL of water. A small portion of this solution is taken and diluted several times. The observation is made to see if the water is still colored after multiple dilutions.
   
   
9. What does the experiment in activity "1.2" show?
   Answer: The experiment in activity "1.2" shows that just a few crystals of potassium permanganate can color a large volume of water (about 1000 L). This suggests that there are millions of tiny particles in one crystal of potassium permanganate, which continue to divide into smaller particles.
   
   
10. How can the same activity be done using Dettol?
    Answer: Instead of potassium permanganate, 2 ml of Dettol can be used in the same activity. Even on repeated dilution, the smell of Dettol can be detected, indicating the presence of tiny particles that retain their properties even after dilution.
    
    
11. What can be said about the size of particles of matter?
    Answer: The particles of matter are extremely small, beyond our imagination.
    
    
12. Explain the activity "1.1" to determine the nature of matter as continuous or particulate.
    To determine the nature of matter, the activity involves taking a 100 mL beaker and filling it halfway with water. Then, some salt or sugar is dissolved using a glass rod. Observations are made on any changes in the water level, where the salt or sugar disappears, and whether the water level changes. The conclusion is reached using the concept that matter is made up of particles, as the dissolved substance spreads throughout the water, indicating the particulate nature of matter.
    
    
13. In Activity "1.2," how is the small size of particles of matter demonstrated?
    In Activity "1.2," a few crystals of potassium permanganate are dissolved in 100 mL of water. Then, small amounts of this solution are taken out and added to larger volumes of clear water several times. Despite the dilution, the water remains colored, showing that just a few crystals of potassium permanganate can color a large volume of water. This indicates that there are millions of tiny particles in one crystal of potassium permanganate that keep dividing into smaller particles. The same activity can be done using 2 mL of Dettol instead of potassium permanganate, and the smell can still be detected even on repeated dilution.
    

    
    Fill in the blanks questions:
    
    

1. As we look at our surroundings, we see a large variety of things with different shapes, sizes, and textures. Everything in this universe is made up of material which scientists have named ____________.
2. The air we breathe, the food we eat, stones, clouds, stars, plants, and animals, even a small drop of water or a particle of sand, every thing is ____________.
3. All the things mentioned above occupy space and have ____________.
4. Early Indian philosophers classified matter in the form of five basic elements - the "Panch Tatva" - air, earth, fire, sky, and ____________.
5. Modern-day scientists have evolved two types of classification of matter based on their physical properties and ____________ nature.
6. In this chapter, we shall learn about matter based on its ____________ properties. Chemical aspects of matter will be taken up in subsequent chapters.
7. For a long time, two schools of thought prevailed regarding the nature of matter. One school believed matter to be continuous like a block of wood, whereas the other thought that matter was made up of ____________ like sand.
8. Let us perform an activity to decide about the nature of matter - is it continuous or ____________?
9. In order to answer these questions, we need to use the idea that matter is made up of ____________.
10. Activity 1.2 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 ____________.

Answers:

1. Matter
2. Matter
3. Mass
4. Water
5. Chemical
6. Physical
7. Particles
8. Particulate
9. Particles
10. Particles

CHARACTERISTICS OF PARTICLES OF MATTER

1. What do the activities involving sugar, salt, Dettol, or potassium permanganate in water demonstrate about particles of matter?
   The activities demonstrate that particles of matter get evenly distributed in water, indicating the presence of enough space between particles.


2. How can you observe the continuous movement of particles of matter?
   You can observe the continuous movement of particles of matter by performing an activity with an unlit incense stick. First, place the incense stick in a corner of your class and note how close you have to go to get its smell. Then, light the incense stick and see if you can still smell it sitting at a distance.


3. What is diffusion, and how does temperature affect it?
   Diffusion is the intermixing of particles of two different types of matter on their own. As temperature rises, the speed of diffusion increases, meaning that particles move faster and intermix more quickly.


4. What does activity 1.6, involving human chains, tell us about the force between particles of matter?
   Activity 1.6 suggests that particles of matter exert force on each other to keep them together. The difficulty of breaking the human chains in different formations indicates variations in the force of attraction between particles.


5. How can you compare the forces holding particles together in substances like an iron nail, a piece of chalk, and a rubber band?
   To compare the forces, you can perform activity 1.7, which involves trying to break the substances by hammering, cutting, or stretching. Observe which substance requires more effort to break, indicating a stronger force of attraction between its particles.


6. Why does the surface of water remain together even when cut with fingers in activity 1.8?
   The surface tension of water is the reason behind its ability to remain together when cut with fingers. It is due to the force of attraction between water molecules at the surface, which creates a "skin" or cohesive layer on the water's surface.


7. What conclusions can be drawn from the observations in activities 1.3, 1.4, and 1.5 regarding the behavior of particles of matter?
   From activities 1.3, 1.4, and 1.5, it can be concluded that particles of matter are in constant motion, their speed increases with temperature, and they spontaneously intermix through diffusion.


8. Explain the variation in the strength of force of attraction between particles of matter as observed in activity 1.6.
   In activity 1.6, the human chains formed with different levels of contact demonstrate that some particles are held together with stronger forces, while others are held with weaker forces. The variations depend on the type of matter and the level of contact between particles.


9. What role does kinetic energy play in the movement of particles of matter?
   Kinetic energy is responsible for the continuous movement of particles of matter. As temperature increases, the kinetic energy of particles also increases, leading to faster movement and increased intermixing through diffusion.


10. In activities 1.1 and 1.2, what did we observe when particles of sugar, salt, Dettol, or potassium permanganate were mixed in water? Explain the significance of this observation in terms of particles of matter.
    We observed that particles of sugar, salt, Dettol, or potassium permanganate got evenly distributed in water, and similarly, when we make tea, coffee, or lemonade, particles of one type of matter get into the spaces between particles of the other. This observation indicates that there is enough space between particles of matter, allowing them to intermix and disperse within a medium.
    
    
11. Describe Activity 1.3 and its outcomes. What can be inferred from the results of this activity?
    Activity 1.3 involves placing an unlit incense stick in a corner and determining how close one needs to be to smell it. Then, the incense stick is lit, and the observations are recorded. The results show that the smell of the incense stick can be detected from a distance even without lighting it. However, after lighting it, the smell becomes more apparent and can be detected from a farther distance. From this activity, it can be inferred that particles of matter are continuously moving, possessing kinetic energy, and when the incense stick is lit, the particles carrying its fragrance move around more actively, spreading the smell farther.
    
    
12. Based on the activities 1.6, 1.7, and 1.8, explain the concept of the force of attraction between particles of matter.
    In Activity 1.6, four groups formed human chains, and one group tried to break the chains. The group holding each other from the back with locked arms was the most difficult to break, indicating that the particles (students) in this group held each other with the maximum force.
    In Activity 1.7, substances like an iron nail, a piece of chalk, and a rubber band were tested for their resistance to breaking. The substance with the greatest force of attraction between its particles was the most difficult to break.
    Finally, in Activity 1.8, cutting the surface of water with fingers was attempted, but it remained intact, suggesting that the particles of water have a force of attraction between them. These activities collectively demonstrate that particles of matter have a force acting between them, which keeps them together. The strength of this force varies among different types of matter, leading to differences in their properties.
    

STATES OF MATTER

CAN MATTER CHANGE ITS STATE?

1. Can matter change its state?
   Yes, matter can change its state. It can exist in three states: solid, liquid, and gas.


2. What happens inside the matter during the change of state?
   During a change of state, such as from solid to liquid or liquid to gas, the internal energy of the particles is affected. The energy supplied by heat causes the particles to gain kinetic energy, leading them to overcome the forces of attraction and change their positions.


3. What happens to the particles of matter during the change of states?
   During the change of states:
   - When transitioning from a solid to a liquid (melting), the particles gain energy, start vibrating more, and break away from their fixed positions.
   - When transitioning from a liquid to a gas (boiling), the particles gain even more energy, move more freely, and overcome the forces of attraction to become gas.


4. How does this change of state take place?
   The change of state takes place by adding or removing heat energy to/from the matter. Increasing the temperature can cause a transition from solid to liquid and from liquid to gas. Decreasing pressure can also lead to the change of state, like in the sublimation of solid directly into gas.


5. What is the latent heat of fusion?
   The latent heat of fusion is the amount of heat energy required to change 1 kg of a solid into a liquid at atmospheric pressure at its melting point. It is the heat energy absorbed during the process of melting without any change in temperature.


6. Can you define the latent heat of vaporisation?
   The latent heat of vaporisation is the amount of heat energy required to change 1 kg of a liquid into a gas at atmospheric pressure at its boiling point. Similar to the latent heat of fusion, it is the heat energy absorbed during the process of vaporization without any change in temperature.


7. What is sublimation and deposition?
   Sublimation is the change of state directly from a solid to a gas without going through the liquid state. Deposition is the reverse process, where a gas directly changes into a solid without becoming a liquid first.


8. Can increasing or decreasing pressure change the state of matter?
   Yes, increasing or decreasing pressure can change the state of matter. Applying pressure and reducing temperature can liquefy gases, and decreasing pressure can cause solids to undergo sublimation and directly become gas.


9. How is solid carbon dioxide (dry ice) related to changes in pressure?
   Solid carbon dioxide (dry ice) is stored under high pressure. When the pressure is decreased to 1 atmosphere, dry ice directly changes from solid to gaseous state without becoming a liquid. This demonstrates how pressure can influence the state of matter.
   
   
10. What is the effect of change of temperature on matter's state?
    Increasing the temperature of solids results in an increase in the kinetic energy of the particles. This causes the particles to vibrate at higher speeds and eventually overcome the forces of attraction between them. Consequently, the solid melts and changes into a liquid state. 
    
    
11. What is the melting point, and why is it significant?
    The minimum temperature at which a solid melts to become a liquid at atmospheric pressure is called its melting point. The melting point is an indication of the strength of the force of attraction between the particles of a solid.
    
    
12. What happens to the heat energy during the melting process?
    During the process of melting, the heat energy supplied does not cause a rise in temperature. Instead, it gets used up in changing the state by overcoming the forces of attraction between the particles. This heat energy is absorbed by the substance without showing any temperature change and is known as latent heat.
    
    
13. What is the boiling point, and why is it important?
    The temperature at which a liquid starts boiling at atmospheric pressure is known as its boiling point. This temperature marks the transition from the liquid state to the gaseous state for the substance.
    What happens when we apply pressure to a gas enclosed in a cylinder?
    
    
14. When pressure is applied to a gas enclosed in a cylinder, the particles of the gas come closer together.
    This reduction in volume increases the density of the gas.
    
    
15. Can changing pressure affect the state of matter?
    Yes, changing pressure can affect the state of matter. By applying pressure and reducing temperature, gases can be liquefied.
    
    
16. What is dry ice, and how is it related to pressure changes?
    Dry ice is solid carbon dioxide (CO2) that is stored under high pressure. On decreasing the pressure to 1 atmosphere, solid CO2 directly converts into a gaseous state without going through the liquid state. This phenomenon is called sublimation.
    
    
17. What is sublimation and deposition?
    Sublimation is the change of state directly from a solid to a gas without going through the liquid state. Deposition is the reverse process, where a gas changes directly to a solid without going through the liquid state.
    
    In conclusion, the state of matter can be changed through the application of heat, pressure, or a combination of both. The rearrangement of particles and the absorption or release of energy lead to the various changes in states of matter, from solid to liquid, liquid to gas, sublimation, and deposition. These processes are essential in understanding the behavior of different substances and their transformations under specific conditions.

Fill in the blanks

1. What are the three states of matter that water can exist in? __________, __________, and __________.
2. During the change of state, what happens to the particles of matter as the temperature increases? The kinetic energy of the particles __________, causing them to __________ with greater speed.
3. The minimum temperature at which a solid melts and becomes a liquid at atmospheric pressure is called its __________ __________.
4. The melting point of ice is __________ K.
5. The process of changing from a solid state to a liquid state is known as __________.
6. What happens to the temperature of a system when a solid is melting, and heat is continuously supplied? The temperature __________ change, as the heat energy is __________ into the contents of the beaker, known as __________ __________.
7. The amount of heat energy required to change 1 kg of a solid into a liquid at atmospheric pressure at its melting point is known as the __________ __________ of __________.
8. The temperature at which a liquid starts boiling at atmospheric pressure is known as its __________ __________.
9. The process of changing directly from a solid state to a gaseous state without becoming a liquid is called __________.
10. The process of changing directly from a gaseous state to a solid state without becoming a liquid is called __________.
11. What happens to gases when pressure is applied and temperature is reduced? __________ and __________ can liquefy gases.
12. What is another name for solid carbon dioxide (CO2) due to its direct conversion into the gaseous state on decrease of pressure? __________ __________.
    
    

Answers:

1. • Solid
   • Liquid
   • Gas
2. increases, vibrate
3. melting point
4. 273.15 K
5. fusion
6. does not, absorbed, latent heat
7. latent heat of fusion
8. boiling point
9. sublimation
10. deposition
11. Applying pressure, reducing temperature
12. Dry ice

EVAPORATION

1. Do we always need to heat or change pressure for changing the state of matter? Can you quote some examples from everyday life where change of state from liquid to vapor takes place without the liquid reaching the boiling point?
   No, changing the state of matter does not always require heating or changing pressure. Evaporation is an example of a change of state from liquid to vapor that occurs below the boiling point. Examples include:Water left uncovered slowly changes into vapor. Wet clothes dry up.
   
   
2. What is evaporation, and how does it occur at any temperature below the boiling point of a liquid? Explain the process of evaporation.
   Evaporation is the process of a liquid turning into vapor at a temperature below its boiling point. The process involves:
   At any given temperature, particles of matter are in constant motion and have different kinetic energies.Some particles at the liquid's surface, with higher kinetic energy, break away from the forces of attraction and become vapor.


3. Describe the activity mentioned in the text to study the factors affecting evaporation. What were the different conditions tested, and how did you record the observations?
   The activity involved three setups with 5 mL of water each:Test tube near a window/fan.Open china dish near a window/fan.Open china dish inside a cupboard/on a shelf.Observations recorded were:Room temperature.Time/days taken for evaporation in each case.Observations on a rainy day.


4. What are the factors that affect the rate of evaporation? Explain how each of the following factors influences the rate of evaporation: surface area, temperature, humidity, and wind speed.
   The rate of evaporation is affected by the following factors:
   Surface area: Increasing surface area increases the rate of evaporation. Temperature: Higher temperature leads to more particles gaining enough kinetic energy to vaporize.
   Humidity: Decreasing humidity increases the rate of evaporation, as air with high water vapor content hinders evaporation.
   Wind speed: Higher wind speed carries away water vapor, decreasing its concentration and promoting evaporation.


5. How does the increase in surface area affect the rate of evaporation? Provide an everyday example to illustrate this concept.
   Increasing the surface area increases the rate of evaporation. For example: When clothes are spread out while drying, more surface area is exposed to air, leading to faster evaporation.


6. How does temperature influence the rate of evaporation? Explain why an increase in temperature leads to a higher rate of evaporation.
   Temperature affects the rate of evaporation by providing more kinetic energy to the liquid particles. With higher temperature:More particles gain sufficient energy to break free from the liquid's surface and become vapor, increasing the evaporation rate.


7. What role does humidity play in the process of evaporation? How does the amount of water vapor in the air affect the rate of evaporation?
   Humidity is the amount of water vapor present in the air. It affects the rate of evaporation as follows:Higher humidity reduces the rate of evaporation since the air is already saturated with water vapor, hindering the escape of more water molecules from the liquid.


8. Explain the relationship between wind speed and the rate of evaporation. Why do clothes dry faster on windy days?
   Wind speed influences the rate of evaporation as follows: Higher wind speed carries away water vapor from the liquid's surface, maintaining a lower concentration of water vapor in the surrounding air. Clothes dry faster on windy days because the wind carries away the evaporated water, promoting a continuous supply of dry air to the wet clothes.


9. How does evaporation cause cooling? Describe the process by which the surroundings become cold when a liquid evaporates in an open vessel.
   Evaporation causes cooling due to energy absorption: When liquid evaporates, particles with higher kinetic energy escape, taking energy from the remaining liquid and surroundings. This energy loss results in a decrease in temperature in the surroundings, making it feel colder.


10. Can you think of any real-life applications of evaporation and its cooling effect? Provide examples where this phenomenon is utilized or observed.
    Some real-life applications of evaporation and its cooling effect include:
    The use of evaporative coolers (swamp coolers) in dry climates to cool indoor air through water evaporation. Sweating in humans and animals cools the body as sweat evaporates from the skin's surface. Drying wet clothes outside or using a fan to speed up the drying process by enhancing evaporation.
    

Class 9 Science Chapter 1 - Matter in our surroundings

Class 9 CBSE Important Questions and Answers Chapter 1- Matter in our surroundings