Class 9 Science Notes Matter in Our Surroundings
1. Introduction to Matter
- Matter: Anything that occupies space, has mass, and can be perceived by senses.
- Examples: Air, water, book, stone.
- Historical Views:
- Ancient Indian philosophers classified matter into Panch Tatva (air, earth, fire, sky, water).
- Modern scientists classify matter based on physical properties (solid, liquid, gas) and chemical nature.
2. Physical Nature of Matter
- Matter is Particulate: Made of tiny particles (atoms/molecules).
- Activity: Dissolving salt in water shows particles occupy space between water particles.
- Size of Particles: Extremely small.
- Activity: Diluting potassium permanganate solution shows even a tiny crystal contains millions of particles.
3. Characteristics of Particles
- Space Between Particles: Allows diffusion (e.g., smell spreading in air).
- Continuous Motion:
- Particles possess kinetic energy.
- Diffusion: Faster in gases > liquids > solids. Increases with temperature.
- Attraction Between Particles:
- Strongest in solids, weaker in liquids, negligible in gases.
- Example: Iron nail (strong attraction) vs. rubber band (weak).
4. States of Matter
| Property | Solid | Liquid | Gas |
|---|---|---|---|
| Shape | Fixed | Takes container’s shape | Takes container’s shape |
| Volume | Fixed | Fixed | Variable |
| Compressibility | Negligible | Low | High |
| Fluidity | Rigid | Flows | Flows easily |
- Examples:
- Solid: Ice, book.
- Liquid: Water, oil.
- Gas: Oxygen, CNG.
5. Change of State
- Effect of Temperature:
- Melting: Solid → Liquid (e.g., ice → water at 0°C).
- Boiling: Liquid → Gas (e.g., water → vapor at 100°C).
- Latent Heat: Hidden heat absorbed/released during state change without temperature change.
- Fusion: Heat for melting.
- Vaporization: Heat for boiling.
- Effect of Pressure:
- Gases can be liquefied by high pressure and low temperature (e.g., LPG, dry ice).
- Sublimation: Direct change from solid → gas (e.g., camphor, dry ice).
6. Evaporation
- Definition: Conversion of liquid to vapor below boiling point (e.g., drying clothes, sweating).
- Factors Affecting Evaporation:
- Surface Area↑ → Evaporation↑.
- Temperature↑ → Evaporation↑.
- Humidity↓ → Evaporation↑.
- Wind Speed↑ → Evaporation↑.
- Cooling Effect: Evaporation absorbs heat from surroundings (e.g., acetone on palm feels cold).
7. Important Concepts
- Why Ice Floats?: Ice has lower density than water.
- Steam Burns More than Boiling Water: Steam has latent heat stored.
- Cotton Clothes in Summer: Absorb sweat and increase evaporation, keeping the body cool.
Key Formulas:
- Density = Mass/Volume
- Temperature Conversion:
- Kelvin to Celsius: °C = K − 273
- Celsius to Kelvin: K = °C + 273
Note: Focus on understanding particle behavior and real-life examples to grasp concepts easily!
Class 9 Science Notes Matter in Our Surroundings
MCQs
Ancient Indian philosophers classified matter into how many basic elements?
a) 3
b) 4
c) 5
d) 6
Answer: c) 5
Which SI unit is used for mass?
a) Cubic metre
b) Kilogram
c) Litre
d) Pascal
Answer: b) Kilogram
In Activity 1.1, dissolving salt in water shows:
a) Matter is continuous
b) Matter is made of particles
c) Water expands
d) Salt loses mass
Answer: b) Matter is made of particles
The idea that matter is particulate is supported by:
a) Hammering a nail
b) Dissolving salt in water
c) Freezing water
d) Burning wood
Answer: b) Dissolving salt in water
Which is NOT a characteristic of matter?
a) Occupies space
b) Has mass
c) Can be felt
d) Can be destroyed
Answer: d) Can be destroyed
The “Panch Tatva” includes:
a) Air, water, fire, earth, metal
b) Air, earth, fire, sky, water
c) Water, stone, air, fire, wood
d) Earth, fire, air, water, light
Answer: b) Air, earth, fire, sky, water
1 litre equals:
a) 1 m³
b) 1 dm³
c) 1 cm³
d) 1 mL
Answer: b) 1 dm³
Activity 1.2 uses which substance to show particle size?
a) Salt
b) Sugar
c) Potassium permanganate
d) Detto
Answer: c) Potassium permanganate
After repeated dilution, the solution remains colored because:
a) Particles are large
b) Particles are small
c) Water is impure
d) Light reflects differently
Answer: b) Particles are small
Detto is used in Activity 1.2 to demonstrate:
a) Color change
b) Smell diffusion
c) Temperature effect
d) Density
Answer: b) Smell diffusion
Particles of matter are:
a) Visible under a microscope
b) Imaginary
c) Small beyond imagination
d) Only in solids
Answer: c) Small beyond imagination
How many dilutions are done in Activity 1.2?
a) 2–3
b) 5–8
c) 10–12
d) 15–20
Answer: b) 5–8
The smell of Dettol persists after dilution due to:
a) Large particles
b) Small particles
c) High density
d) Low temperature
Answer: b) Small particles
What property of particles is highlighted in Activity 1.2?
a) Attraction
b) Motion
c) Size
d) Charge
Answer: c) Size
Diffusion is fastest in:
a) Solids
b) Liquids
c) Gases
d) Plasma
Answer: c) Gases
Particles possess:
a) Potential energy
b) Kinetic energy
c) Magnetic energy
d) Static energy
Answer: b) Kinetic energy
Heating increases particle motion because:
a) Bonds break
b) Kinetic energy rises
c) Volume decreases
d) Density increases
Answer: b) Kinetic energy rises
In Activity 1.3, lighting an incense stick shows:
a) Particles attract
b) Particles move
c) Particles are rigid
d) Particles repel
Answer: b) Particles move
Ink spreads faster in hot water due to:
a) Lower density
b) Higher kinetic energy
c) More space
d) Stronger bonds
Answer: b) Higher kinetic energy
Diffusion in solids is:
a) Very fast
b) Slow
c) Absent
d) Random
Answer: b) Slow
Particles of matter intermix through:
a) Compression
b) Diffusion
c) Sublimation
d) Condensation
Answer: b) Diffusion
Which state of matter has no fixed shape but fixed volume?
a) Solid
b) Liquid
c) Gas
d) Plasma
Answer: b) Liquid
Liquids are called “fluid” because:
a) They have high density
b) They can flow
c) They are compressible
d) They have rigid particles
Answer: b) They can flow
Aquatic animals survive in water due to the presence of:
a) Dissolved oxygen
b) Dissolved nitrogen
c) Salt particles
d) Carbon monoxide
Answer: a) Dissolved oxygen
Which state of matter is highly compressible?
a) Solid
b) Liquid
c) Gas
d) None
Answer: c) Gas
What property of gas allows it to fill a container completely?
a) High density
b) Rigidity
c) Fluidity
d) Random motion of particles
Answer: d) Random motion of particles
CNG is used as fuel in vehicles because gases are:
a) Inflammable
b) Highly compressible
c) Lightweight
d) Non-reactive
Answer: b) Highly compressible
The smell of food reaches us due to:
a) Evaporation
b) Diffusion of gas particles
c) Sublimation
d) Condensation
Answer: b) Diffusion of gas particles
Dry ice is:
a) Solid water
b) Solid carbon dioxide
c) Solid oxygen
d) Liquid nitrogen
Answer: b) Solid carbon dioxide
Gases exert pressure on container walls because:
a) Particles are stationary
b) Particles collide with walls
c) Particles attract each other
d) Particles are heavy
Answer: b) Particles collide with walls
The SI unit of pressure is:
a) Kelvin
b) Pascal
c) Newton
d) Joule
Answer: b) Pascal
Which gas is supplied in cylinders to hospitals?
a) Nitrogen
b) Oxygen
c) Hydrogen
d) Carbon dioxide
Answer: b) Oxygen
LPG cylinders contain gas in:
a) Solid state
b) Liquid state
c) Compressed gaseous state
d) Plasma state
Answer: c) Compressed gaseous state
Deposition refers to the direct change from:
a) Solid → Gas
b) Gas → Solid
c) Liquid → Gas
d) Gas → Liquid
Answer: b) Gas → Solid
The interconversion of states of matter depends on:
a) Temperature only
b) Pressure only
c) Both temperature and pressure
d) Humidity
Answer: c) Both temperature and pressure
The melting point of ice is:
a) 0°C
b) 100°C
c) 273 K
d) Both a and c
Answer: d) Both a and c
Latent heat is “hidden” because it:
a) Cannot be measured
b) Changes state without temperature rise
c) Is absorbed by the surroundings
d) Is released slowly
Answer: b) Changes state without temperature rise
Boiling is a:
a) Surface phenomenon
b) Bulk phenomenon
c) Chemical change
d) Reversible process
Answer: b) Bulk phenomenon
The boiling point of water is:
a) 273 K
b) 373 K
c) 100 K
d) 0 K
Answer: b) 373 K
Particles in steam have more energy than water at 100°C because they absorb:
a) Latent heat of fusion
b) Latent heat of vaporization
c) Kinetic energy
d) Potential energy
Answer: b) Latent heat of vaporization
During melting, the temperature of ice remains constant because heat is used to:
a) Break intermolecular forces
b) Increase particle speed
c) Convert ice to vapor
d) Cool the surroundings
Answer: a) Break intermolecular forces
Which term describes the change of solid to liquid?
a) Sublimation
b) Fusion
c) Vaporization
d) Condensation
Answer: b) Fusion
Sublimation is demonstrated using:
a) Ice
b) Camphor
c) Salt
d) Water
Answer: b) Camphor
Dry ice sublimes at:
a) High pressure
b) Low pressure
c) Room temperature
d) High humidity
Answer: b) Low pressure
The process of gas turning directly into solid is called:
a) Sublimation
b) Deposition
c) Condensation
d) Freezing
Answer: b) Deposition
Applying pressure on a gas can:
a) Convert it to plasma
b) Liquefy it
c) Increase its volume
d) Decrease kinetic energy
Answer: b) Liquefy it
Solid CO₂ is called dry ice because it:
a) Is cold
b) Does not melt into liquid
c) Is white
d) Absorbs moisture
Answer: b) Does not melt into liquid
Which factor does NOT affect the state of matter?
a) Temperature
b) Pressure
c) Humidity
d) Both a and b
Answer: c) Humidity
The state of matter depends on:
a) Particle size
b) Particle motion and spacing
c) Particle color
d) Particle charge
Answer: b) Particle motion and spacing
Evaporation occurs:
a) Only at boiling point
b) Below boiling point
c) In closed containers
d) At 0°C
Answer: b) Below boiling point
Wet clothes dry faster on a windy day because:
a) Humidity decreases
b) Wind increases evaporation rate
c) Temperature drops
d) Clothes absorb heat
Answer: b) Wind increases evaporation rate
Cotton clothes are preferred in summer because they:
a) Reflect sunlight
b) Absorb sweat and promote evaporation
c) Are waterproof
d) Trap air
Answer: b) Absorb sweat and promote evaporation
Water droplets on a cold glass are due to:
a) Evaporation
b) Condensation
c) Sublimation
d) Diffusion
Answer: b) Condensation
Ice at 273 K cools better than water at 273 K because it:
a) Has higher density
b) Absorbs latent heat during melting
c) Is a solid
d) Reflects heat
Answer: b) Absorbs latent heat during melting
Steam causes severe burns because it:
a) Has high temperature
b) Releases latent heat of vaporization
c) Is invisible
d) Expands rapidly
Answer: b) Releases latent heat of vaporization
The unit of latent heat is:
a) J/kg
b) J/K
c) kg/m³
d) Pa
Answer: a) J/kg
One-Liner Questions & Answers
- What is matter?
Answer: Anything that occupies space and has mass. - Name the five elements in “Panch Tatva”.
Answer: Air, earth, fire, sky, water. - What is the SI unit of mass?
Answer: Kilogram (kg). - What happens when salt dissolves in water?
Answer: Salt particles occupy spaces between water particles. - How small are particles of matter?
Answer: Extremely small, beyond imagination. - What is diffusion?
Answer: Mixing of particles of two substances on their own. - Why do gases diffuse faster than solids?
Answer: Gases have higher kinetic energy and space between particles. - What property allows aquatic animals to breathe in water?
Answer: Dissolved oxygen in water. - Why are gases highly compressible?
Answer: Large spaces exist between gas particles. - What is the boiling point of water in Kelvin?
Answer: 373 K. - Define sublimation.
Answer: Direct change of solid to gas without becoming liquid. - Name a substance that undergoes sublimation.
Answer: Camphor. - What is dry ice?
Answer: Solid carbon dioxide (CO₂). - Why does evaporation cause cooling?
Answer: It absorbs heat from the surroundings. - Convert 300 K to Celsius.
Answer: 27°C. - Why does ice float on water?
Answer: Ice has lower density than water. - What is latent heat of fusion?
Answer: Heat required to melt 1 kg of solid at its melting point. - Why are cotton clothes preferred in summer?
Answer: They absorb sweat and promote evaporation. - What causes water droplets on a cold glass?
Answer: Condensation of water vapor from air. - Why does steam cause severe burns?
Answer: It releases latent heat of vaporization. - What is the melting point of ice?
Answer: 0°C (273 K). - Name a gas used in LPG cylinders.
Answer: Propane/Butane (compressed gas). - What determines the state of matter?
Answer: Temperature and pressure. - What is deposition?
Answer: Direct change of gas to solid without becoming liquid. - Why does a wooden table remain solid?**
Answer: Its particles have strong intermolecular forces.
Fill-in-the-Blanks
- Anything that occupies space and has mass is called __.
Answer: matter - The five basic elements in “Panch Tatva” are air, earth, fire, sky, and __.
Answer: water - The SI unit of mass is __.
Answer: kilogram (kg) - When salt dissolves in water, its particles occupy the spaces between __ particles.
Answer: water - The experiment with potassium permanganate shows that particles of matter are __.
Answer: extremely small - The smell of hot sizzling food reaches us due to the rapid __ of gas particles.
Answer: diffusion - Liquids take the shape of their container because they are __.
Answer: fluid - Gases exert pressure on container walls due to the __ of their particles.
Answer: random motion - Solid carbon dioxide is commonly known as __.
Answer: dry ice - The process of converting a solid directly into gas is called __.
Answer: sublimation - The temperature at which a solid melts is called its __.
Answer: melting point - The latent heat absorbed during vaporization is stored as __ energy in steam.
Answer: latent - Evaporation causes cooling because it absorbs heat from the __.
Answer: surroundings - Ice floats on water because it has __ density than water.
Answer: lower - Cotton clothes are preferred in summer as they help in __ evaporation of sweat.
Answer: increasing - Water droplets on a cold glass are formed due to __ of water vapor.
Answer: condensation - The SI unit of pressure is __.
Answer: Pascal (Pa) - The minimum temperature at which a liquid boils is called its __.
Answer: boiling point - A sponge can be compressed because it has trapped __ in its holes.
Answer: air - The intermixing of particles of different substances on their own is called __.
Answer: diffusion
Long Answer Questions
1. Explain the characteristics of particles of matter with suitable experiments.
Answer:
Particles of matter exhibit three key characteristics:
- Space Between Particles:
- Experiment: Dissolving salt/sugar in water (Activity 1.1). The salt disappears as its particles occupy spaces between water particles, showing matter is particulate.
- Continuous Motion:
- Experiment: Diffusion of potassium permanganate in water (Activity 1.2). Even after repeated dilution, the solution remains colored, proving particles are tiny and in constant motion.
- Attraction Between Particles:
- Experiment: Comparing the rigidity of iron, chalk, and rubber (Activity 1.7). Iron resists breaking due to strong intermolecular forces, while rubber stretches due to weaker forces.
Conclusion: These experiments confirm that matter is made of tiny, moving particles with spaces between them and varying forces of attraction.
2. Describe the three states of matter and their properties with examples.
Answer:
- Solid State:
- Properties: Fixed shape/volume, rigid, incompressible.
- Example: Ice, iron nail.
- Particle Behavior: Particles vibrate in fixed positions with strong intermolecular forces.
- Liquid State:
- Properties: No fixed shape (takes container’s shape), fixed volume, fluid, slightly compressible.
- Example: Water, oil.
- Particle Behavior: Particles move freely but remain close due to moderate forces.
- Gaseous State:
- Properties: No fixed shape/volume, highly compressible, fills the container.
- Example: Oxygen, LPG.
- Particle Behavior: Particles move randomly at high speed with negligible attraction.
Key Difference: Solids have maximum order and rigidity, gases have maximum disorder and kinetic energy.
3. Discuss the interconversion of states of matter with the effect of temperature and pressure.
Answer:
States of matter change due to variations in temperature and pressure:
- Effect of Temperature:
- Solid → Liquid (Melting): Heating increases kinetic energy, breaking intermolecular forces (e.g., ice to water at 0°C).
- Liquid → Gas (Vaporization): Particles gain energy to escape as gas (e.g., water boils at 100°C).
- Gas → Liquid (Condensation): Cooling reduces energy, particles come closer (e.g., dew formation).
- Effect of Pressure:
- Gas → Liquid (Liquefaction): High pressure compresses gas particles (e.g., LPG cylinders).
- Solid ↔ Gas (Sublimation/Deposition): Camphor sublimes on heating; CO₂ gas deposits as dry ice under high pressure.
Latent Heat: Energy absorbed/released during state change without temperature change (e.g., ice at 0°C absorbs latent heat to melt).
4. Explain the factors affecting evaporation and how evaporation causes cooling.
Answer:
Factors:
- Surface Area: Larger surface area (e.g., spread clothes) increases evaporation.
- Temperature: Higher temperature provides energy for particles to escape.
- Humidity: Low humidity (dry air) enhances evaporation.
- Wind Speed: Wind removes vapor, maintaining a concentration gradient.
Cooling Effect:
Evaporation absorbs latent heat from the surroundings. For example, acetone on the palm absorbs heat from the skin, causing a cooling sensation. Similarly, sweating cools the body as sweat evaporates.
5. Why does ice float on water? Explain the consequences of this property.
Answer:
Reason: Ice has a lower density than water due to its hexagonal structure, creating gaps between particles.
Consequences:
- Ecological Impact: Ice layers insulate water bodies, protecting aquatic life in winters.
- Climate Regulation: Polar ice caps regulate Earth’s temperature by reflecting sunlight.
6. Compare and contrast boiling and evaporation.
Answer:
| Aspect | Boiling | Evaporation |
|---|---|---|
| Temperature | Occurs at boiling point (100°C). | Occurs at any temperature below BP. |
| Phenomenon | Bulk process (entire liquid heats). | Surface process. |
| Energy Source | External heat. | Ambient heat. |
| Bubbles | Forms bubbles. | No bubbles. |
| Rate | Rapid. | Slow. |
Example: Boiling water in a kettle vs. drying clothes.
7. Discuss the significance of latent heat in daily life with examples.
Answer:
Latent Heat: Energy absorbed/released during state change without temperature change.
- Cooling Drinks: Ice absorbs latent heat from drinks, cooling them.
- Weather Patterns: Evaporation of seawater (absorbing latent heat) influences humidity and rainfall.
- Cooking: Steam releases latent heat when condensing, cooking food faster (e.g., steamers).
- Human Body: Sweat evaporates using latent heat, regulating body temperature.