CBSE Class 9 Science Chapter 1 Notes

Matter in Our Surroundings CBSE Class 9 Science Chapter 1 Notes are available here. These notes have been created by the subject experts of our website CBSE Wale.

Matter in Our Surroundings CBSE Class 9 Science Chapter 1 Notes

Matter

• Definition: Matter is a substance that possesses mass and occupies space.
• Study of Matter: Chemistry is the science that studies matter. This study encompasses various aspects, including its composition, structure, properties, and reactions.
• Classification of Matter:
  • Chemical Composition:
    1. Elements: Substances composed of only one type of atom. They cannot be broken down into simpler substances by chemical means.
    2. Compounds: Substances composed of two or more different types of atoms chemically bonded together in fixed ratios.
    3. Mixtures: Combinations of two or more substances that are physically mixed together but not chemically bonded.
  • Characteristic Properties:
    • Metals: Elements characterized by luster, conductivity, malleability, and ductility.
    • Non-metals: Elements that lack metallic properties and are generally poor conductors of heat and electricity.
    • Metalloids: Elements that possess properties intermediate between metals and non-metals.

Physical Nature of Matter

Activity: Investigating the Nature of Matter

1. Objective: To determine whether matter is continuous or particulate.
2. Materials Required:
   • 100 mL beaker
   • Water
   • Salt or sugar
   • Glass rod
3. Procedure:
   • Fill half the beaker with water and mark the water level.
   • Dissolve salt/sugar in the water using a glass rod.
   • Observe any changes in the water level.
   • Analyze the disappearance of salt/sugar and its dispersion in water.
   • Determine if the level of water changes.
4. Observations and Inferences:
   • The salt/sugar disappears upon dissolution and spreads throughout the water.
   • There is no significant change in the level of water.
   • Conclusion: Matter exhibits properties consistent with being composed of particles rather than being continuous.

Understanding Particle Size:

1. Objective: To comprehend the minuscule size of particles in matter.
2. Experiment:
   • Take 2–3 crystals of potassium permanganate and dissolve them in 100 mL of water.
   • Transfer 10 mL of this solution into 90 mL of clear water.
   • Repeat the process of dilution 5 to 8 times.
   • Observe if the water retains its color.
3. Observations:
   • Even a few crystals of potassium permanganate can color a large volume of water.
   • The water remains colored after multiple dilutions, indicating the presence of tiny particles.
4. Conclusion:
   • The experiment highlights that a single crystal of potassium permanganate contains millions of tiny particles, which continue to divide into smaller units.
   • This demonstrates the extremely small size of particles in matter, far beyond human imagination.

Additional Experiment:

1. Objective: To further illustrate the small size of particles in matter.
2. Procedure:
   • Substitute potassium permanganate with 2 mL of Dettol.
   • Detect the smell of Dettol even after repeated dilutions.
3. Observation:
   • The smell of Dettol persists even after multiple dilutions, indicating the presence of extremely small particles.
4. Conclusion:
   • The persistence of smell, even upon dilution, reinforces the concept of matter being composed of particles of infinitesimal size.

Characteristics of Particles of Matter

1. Particles of Matter Have Space Between Them

• When we observe substances like sugar, salt, Dettol, or potassium permanganate dissolving in water, we notice that they spread evenly throughout the water.
• Similarly, when preparing beverages like tea, coffee, or lemonade, the particles of one substance mix with those of another, indicating that there is space between particles of matter.

Evidence of Space Between Particles:

1. Even Distribution in Solutions:
   • Sugar, salt, Dettol, and potassium permanganate dissolve in water and disperse uniformly throughout.
   • This uniform spreading suggests that there is space available for the particles to occupy within the liquid.
2. Mixing of Substances:
   • In the preparation of beverages such as tea, coffee, or lemonade, the particles of one substance intermingle with those of another.
   • This mixing implies that there is sufficient space between the particles for them to move and mix freely.

Implications of Particle Spacing:

• The presence of space between particles of matter has several implications:

1. Fluidity and Mobility:
   • The ability of particles to move and mix freely within a substance contributes to its fluidity.
   • Liquids and gases, in particular, exhibit this characteristic due to the significant spaces between their particles.
2. Solubility:
   • Solids dissolve in liquids because their particles can occupy the spaces between the particles of the solvent.
   • This phenomenon explains why substances dissolve and form solutions.
3. Expansion and Contraction:
   • Changes in temperature can cause particles to either spread out (expand) or come closer together (contract).
   • This behavior is a result of the spaces between particles accommodating the changes in volume.

2. Particles of Matter are Continuously Moving

• In our daily experiences, we encounter evidence that particles of matter are in constant motion. This motion, known as kinetic energy, underlies various phenomena such as diffusion and expansion.

Activity 1: Incense Stick Observation

• Placing an unlit incense stick in a corner of the class reveals that its smell is detectable only when close.
• Upon lighting the incense stick, its smell becomes noticeable even from a distance.
• Observation: The movement of air carries the scent molecules further when the incense stick is lit.

Activity 2: Ink and Honey Experiment

• Adding a drop of ink into one glass and honey into another showcases immediate dispersal along the sides of the containers.
• Over time, the ink spreads uniformly throughout the water, while the honey remains localized.
• Observation: Ink molecules move and disperse freely in water, showing continuous motion.
• The movement of ink molecules gradually equalizes the concentration throughout the water.

Activity 3: Copper Sulphate/Potassium Permanganate Dissolution

• Dropping crystals of these substances into glasses of hot and cold water respectively results in observation of particle movement.
• Initially, crystals settle at the bottom, but gradually, their color spreads throughout the water.
• Observation: Particles of the solute move and mix with the solvent particles, leading to uniform dispersion of color.
• The rate of mixing increases with temperature due to enhanced particle movement.

Key Concept:

• Kinetic Energy of Particles: Particle motion, or kinetic energy, is inherent to matter and increases with temperature.
• Diffusion: Spontaneous intermixing of particles between substances due to their continuous motion and occupation of spaces.
• Effect of Temperature on Diffusion: Higher temperatures result in faster particle movement and consequently accelerated diffusion rates.

3. Particles of Matter Attract Each Other

Activity 1: Human Chains

• Objective: To observe the strength of inter-particle attraction by forming human chains and testing their resistance to being broken.
• Procedure:
  • Form four groups.
  • Group 1: Lock arms from the back.
  • Group 2: Hold hands to form a chain.
  • Group 3: Touch each other with only their fingertips to form a chain.
  • Group 4: Attempt to break the chains by running around them.
• Observations and Analysis:
  • The human chain formed by Group 1 (locking arms from the back) was the most difficult to break.
  • The strength of inter-particle attraction was highest in Group 1 because locking arms creates a stronger bond compared to holding hands or touching fingertips.

Activity 2: Breaking Substances

• Objective: To determine the strength of inter-particle attraction in different substances by attempting to break them.
• Materials: Iron nail, chalk, rubber band.
• Procedure:
  • Attempt to break the iron nail, chalk, and rubber band by hammering, cutting, or stretching them.
• Observations and Analysis:
  • The iron nail is the most difficult to break, indicating strong inter-particle attraction.
  • Chalk is relatively easier to break compared to the iron nail.
  • The rubber band is the easiest to break, suggesting weaker inter-particle attraction.

Activity 3: Cutting Water

• Objective: To observe the surface tension of water and understand the force of attraction between water particles.
• Procedure:
  • Take some water in a container.
  • Attempt to cut the surface of the water with your fingers.
• Observations and Analysis:
  • It is not possible to cut the surface of water with fingers.
  • The surface of water remains intact due to cohesive forces between water molecules, known as surface tension.

Conclusion: The above activities demonstrate that particles of matter attract each other, and this attraction keeps the particles together. The strength of this force of attraction varies among different substances. In activities 1 and 2, stronger bonds were observed in substances like iron, whereas weaker bonds were observed in substances like rubber. Activity 3 illustrates the cohesive forces present in water, which prevent its surface from being easily broken.

States of Matter

1. The Solid State

Activity: Exploring Properties of Solids

• Objective: To understand the properties of solids through observation and experimentation.
• Materials: Pen, book, needle, wooden stick, pencil, rubber band, sugar, salt, sponge.
• Procedure:
  1. Sketch the shape of the provided articles (pen, book, needle, wooden stick) by moving a pencil around them in a notebook.
  2. Observe whether these articles have a definite shape, distinct boundaries, and a fixed volume.
  3. Experiment by hammering, pulling, or dropping the articles to observe their behavior under force.
  4. Investigate whether these solids can diffuse into each other.
  5. Attempt to compress the solids by applying force.
• Observations and Analysis:
  • All the provided articles (pen, book, needle, wooden stick) have a definite shape, distinct boundaries, and fixed volumes.
  • When subjected to force, they may break but maintain their shape, indicating rigidity.
  • These solids do not diffuse into each other.
  • Compression of these solids is difficult, indicating negligible compressibility.

Considerations:

1. Rubber Band:
   • The rubber band changes its shape on stretching but regains its original shape when the force is removed.
   • Excessive force can cause it to break.
   • Despite its ability to change shape temporarily, it is considered a solid due to its ability to regain its original form.
2. Sugar and Salt:
   • Sugar and salt maintain their shape regardless of the container they are placed in.
   • The shape of individual sugar or salt crystals remains fixed, whether in hand, plate, or jar.
   • They exhibit characteristics of solids by having a fixed shape and volume.
3. Sponge:
   • A sponge is solid but compressible.
   • It contains minute holes in which air is trapped.
   • When pressure is applied, the air is expelled, allowing the sponge to compress.
   • Despite compressibility, a sponge maintains its solid state due to its molecular structure.

Conclusion: The activities conducted demonstrate the properties of solids. Solids have a definite shape, distinct boundaries, and fixed volumes. They resist changes in shape under external force, exhibiting rigidity. While some solids, like rubber bands and sponges, may display unique properties such as elasticity or compressibility, they are still classified as solids due to their overall behavior and molecular structure.

2. The Liquid State

Activity: Exploring Properties of Liquids

• Objective: To investigate the properties of liquids through observation and experimentation.
• Materials: (a) Water, cooking oil, milk, juice, cold drink. (b) Containers of different shapes with a 50 mL mark.
• Procedure:
  1. Spill each liquid on the floor to observe its behavior.
  2. Measure 50 mL of one liquid and transfer it into different containers one by one. Note any changes in volume.
  3. Observe if the shape of the liquid remains the same when transferred to different containers.
  4. Pour the liquid from one container to another and note how easily it flows.
• Observations and Analysis:
  • Liquids have no fixed shape but have a fixed volume.
  • They take up the shape of the container they are placed in.
  • When transferred to different containers, the volume of the liquid remains the same.
  • The shape of the liquid changes according to the shape of the container.
  • Liquids flow easily from one container to another, indicating fluidity.

Diffusion in Liquids:

• Solids and liquids can diffuse into liquids.
• Gases from the atmosphere, especially oxygen and carbon dioxide, dissolve in water.
• This is crucial for the survival of aquatic animals and plants as dissolved oxygen supports their respiration.

Importance of Diffusion in Liquids:

• All living creatures require oxygen for survival.
• Aquatic animals can respire underwater due to the presence of dissolved oxygen.
• Solids, liquids, and gases can diffuse into liquids.
• The rate of diffusion in liquids is higher than that in solids due to the greater freedom of movement and spacing between particles in the liquid state.

Conclusion: The activities conducted illustrate the properties of liquids. Liquids have a fixed volume but no fixed shape, taking the shape of the container they are placed in. They exhibit fluidity, allowing them to flow easily. The process of diffusion in liquids is crucial for the survival of aquatic life, as dissolved oxygen supports respiration. Liquids allow for the easy movement of particles and have a higher rate of diffusion compared to solids due to the greater freedom of movement between particles.

3. The Gaseous State

Activity: Observing Compressibility of Gases

• Objective: To investigate the compressibility of gases compared to solids and liquids through experimentation.
• Materials:
  • Three 100 mL syringes with rubber corks
  • Water
  • Pieces of chalk
  • Vaseline
• Procedure:
  1. Close the nozzles of three syringes with rubber corks.
  2. Remove the pistons from all syringes.
  3. Leave one syringe untouched, fill water in the second, and pieces of chalk in the third.
  4. Insert the pistons back into the syringes, applying vaseline for smooth movement.
  5. Attempt to compress the contents by pushing the piston in each syringe.
  6. Observe and note the ease of compressibility in each case.
• Observations and Analysis:
  • Gases are highly compressible compared to solids and liquids.
  • The piston was easily pushed in the syringe containing air compared to water or chalk.
  • This indicates that gases can be compressed to a greater extent than solids or liquids.

Applications of Compressed Gases:

• Liquefied petroleum gas (LPG) used for cooking and oxygen cylinders used in hospitals are examples of compressed gases.
• Compressed natural gas (CNG) is used as fuel in vehicles due to its high compressibility, allowing large volumes to be stored in small cylinders for easy transportation.

Diffusion of Gases:

• Gases exhibit rapid diffusion due to the high speed and random movement of particles.
• Aroma particles from cooking food mix with air particles and diffuse quickly, reaching our nostrils and even farther away.
• Compared to solids and liquids, gases show a much faster rate of diffusion due to the high speed and larger space between particles.

Pressure Exerted by Gases:

• In the gaseous state, particles move randomly at high speeds, colliding with each other and the walls of the container.
• The pressure exerted by a gas is the result of the force exerted by gas particles per unit area on the walls of the container.

Conclusion: The activity demonstrates the high compressibility of gases compared to solids and liquids. Gases can be compressed to a much greater extent, making them suitable for various applications such as cooking fuel and medical oxygen supply. Additionally, gases exhibit rapid diffusion due to the high speed and random movement of particles, leading to the quick spread of aroma particles. The pressure exerted by gases is a result of the force exerted by gas particles colliding with the walls of the container, showcasing the dynamic nature of gas particles in motion.

Change in the State of Matter

1. Effect of Change of Temperature

Activity: Observing Changes in State of Matter with Temperature

• Objective: To observe the changes in state of matter with temperature using ice and water.
• Materials:
  • Beaker
  • Ice (about 150 g)
  • Laboratory thermometer
  • Glass rod
  • Heat source (e.g., Bunsen burner)
• Procedure:
  1. Place about 150 g of ice in a beaker and suspend a laboratory thermometer so that its bulb is in contact with the ice.
  2. Heat the beaker on a low flame and note the temperature when the ice starts melting.
  3. Continue heating and note the temperature when all the ice has converted into water.
  4. Insert a glass rod in the beaker and continue heating while stirring until the water starts boiling.
  5. Keep a careful eye on the thermometer reading until most of the water has vaporized.
  6. Record observations for the conversion of water from the liquid state to the gaseous state.
• Observations and Analysis:
  • On increasing the temperature, the kinetic energy of particles in ice increases.
  • The increased kinetic energy causes the particles to vibrate with greater speed, overcoming the forces of attraction between them.
  • When the melting point is reached, the ice melts and converts into water, indicating a change from the solid to the liquid state.
  • The temperature remains constant during the phase change, indicating absorption of latent heat without a rise in temperature.
  • The temperature at which a solid melts to become a liquid at atmospheric pressure is called its melting point.
  • The melting point of ice is 273.15 K, and the process of melting is known as fusion.
  • Similarly, when the boiling point is reached, the liquid starts changing into gas, indicating a change from the liquid to the gaseous state.
  • The temperature at which a liquid starts boiling at atmospheric pressure is called its boiling point.
  • The boiling point of water is 373 K (100°C), and the process of boiling is a bulk phenomenon.

Latent Heat and Phase Changes:

• Heat energy is absorbed during phase changes without causing a change in temperature.
• This absorbed heat energy is known as latent heat, where “latent” means hidden.
• The latent heat of fusion is the amount of heat energy required to change 1 kg of a solid into liquid at atmospheric pressure at its melting point.
• Similarly, the latent heat of vaporization is the amount of heat energy required to change 1 kg of a liquid into gas at atmospheric pressure at its boiling point.

Sublimation and Deposition:

• Sublimation is the change of state directly from solid to gas without passing through the liquid state.
• Deposition is the change of state directly from gas to solid without passing through the liquid state.

Conclusion: The activity demonstrates the effects of changing temperature on the state of matter. As temperature increases, solids melt to become liquids, and liquids boil to become gases. During these phase changes, latent heat is absorbed or released without a change in temperature. Sublimation and deposition also showcase direct state changes without an intermediate liquid phase. Understanding these processes helps in comprehending the behavior of matter under different conditions.

2. Effect of Change of Pressure

• The states of matter differ due to variations in the distances between constituent particles.
• This topic explores the impact of changing pressure on the state of matter.

Effect of Pressure on Gases:

• When pressure is applied and a gas enclosed in a cylinder is compressed, the particles within the gas come closer together.
• The application of pressure can lead to changes in the state of matter.

Liquefaction of Gases:

• Applying pressure and reducing temperature can liquefy gases.
• Solid carbon dioxide (CO2), also known as dry ice, is an example of a substance stored under high pressure.
• Solid CO2 directly converts into the gaseous state upon a decrease in pressure to 1 atmosphere without transitioning through the liquid state.

Conclusion:

• Pressure and temperature are crucial factors determining the state of a substance, whether it exists as a solid, liquid, or gas.
• Understanding the relationship between pressure and the state of matter is essential for various applications and processes, such as gas liquefaction and the handling of substances like dry ice.

Evaporation

• Evaporation is the process by which a liquid changes into vapor at a temperature below its boiling point.
• This topic explores evaporation as a natural phenomenon occurring without the need for heating or changes in pressure.

Examples of Evaporation in Everyday Life:

1. Water Left Uncovered:
   • When water is left uncovered, it slowly changes into vapor.
   • This process occurs at room temperature without the need for heating.
   • The water molecules at the surface gain enough kinetic energy to overcome the forces of attraction and escape into the air as vapor.
2. Drying of Wet Clothes:
   • Wet clothes dry up over time due to evaporation.
   • Water molecules on the surface of the clothes gain sufficient energy from the surroundings to break free and transform into vapor.

Mechanism of Evaporation:

• Particles of matter are always in motion, with varying amounts of kinetic energy at a given temperature.
• In liquids, a fraction of particles at the surface possesses higher kinetic energy.
• These particles overcome the attractive forces of neighboring particles and escape into the surrounding space as vapor.
• Evaporation occurs continuously, with molecules constantly entering and leaving the liquid phase.

Factors Affecting Evaporation

• Evaporation is influenced by various factors such as temperature, surface area, humidity, and wind speed.

Activity: Observing Factors Affecting Evaporation

• Objective: To investigate the effects of temperature, surface area, and wind speed on the rate of evaporation.
• Materials:
  • Test tubes
  • China dishes
  • Water
  • Fan
  • Cupboard/shelf
• Procedure:
  1. Take 5 mL of water in a test tube and place it near a window or under a fan.
  2. Take another 5 mL of water in an open china dish and place it near a window or under a fan.
  3. Take a third 5 mL of water in an open china dish and place it inside a cupboard or on a shelf.
  4. Record the room temperature.
  5. Record the time or days taken for evaporation in each case.
  6. Repeat the above steps on a rainy day and record observations.
• Observations and Analysis:
  • The rate of evaporation is affected by:
    • Surface Area: Increasing the surface area enhances the rate of evaporation. Spreading out clothes for drying increases the surface area exposed to air, facilitating faster evaporation.
    • Temperature: Higher temperatures provide more kinetic energy to water molecules, increasing the rate of evaporation.
    • Humidity: Decreased humidity allows for faster evaporation as the air can hold more water vapor. Conversely, high humidity reduces the rate of evaporation.
    • Wind Speed: Higher wind speeds result in faster evaporation. Wind carries away water vapor from the surface, maintaining lower humidity and promoting evaporation.

How Does Evaporation Cause Cooling?

• Evaporation is not only a process of changing a liquid into vapor but also a phenomenon that can cause cooling.
• This topic explores the mechanism through which evaporation leads to cooling and provides examples of cooling effects in everyday life.

Mechanism of Evaporative Cooling:

• In an open vessel, as a liquid evaporates, its particles absorb energy from the surroundings to compensate for the energy lost during evaporation.
• This absorption of energy from the surroundings results in a decrease in temperature, making the surroundings feel cooler.

Examples of Evaporative Cooling:

1. Effect of Acetone on Skin:
   • When acetone (nail polish remover) is poured on the palm, the liquid evaporates, absorbing energy from the palm or surrounding environment.
   • This evaporation causes the palm to feel cool due to the transfer of heat energy from the palm to the evaporating acetone molecules.
2. Sprinkling Water on Hot Surfaces:
   • After a hot sunny day, people sprinkle water on the roof or open ground to cool the surface.
   • The high latent heat of vaporization of water facilitates evaporation, absorbing heat energy from the hot surface and cooling it down.
3. Effect of Cotton Clothes in Summer:
   • Wearing cotton clothes in summer helps in staying cool due to their ability to absorb sweat and facilitate evaporation.
   • Cotton is a good absorber of water, allowing sweat to be absorbed and exposed to the atmosphere for efficient evaporation, cooling the body.
4. Water Droplets on the Outer Surface of a Glass:
   • When ice-cold water is placed in a glass, water droplets form on the outer surface of the glass.
   • The water vapor present in the air comes in contact with the cold surface of the glass, loses energy, and condenses into liquid droplets due to the decrease in temperature.