Table of Contents
Matter In Our Surroundings – Worksheet with Answer Key
1. Conceptual Questions (Definition-Based)
- What is matter? Give examples.
- Define the term “diffusion.”
- What is the difference between boiling and evaporation?
- What is sublimation? Give an example.
- Define latent heat of fusion and latent heat of vaporization.
Also Check – Rapid Revision –Chapter 1- Matter In Our Surroundings – Class 9 Science
Also Check – Chapter 1 -MATTER IN OUR SURROUNDINGS -Class 9 – Simplified detailed Notes
2. Reasoning-Based Questions
- Why does the smell of hot food spread faster than cold food?
- Why does ice float on water even though it is solid?
- Why do we feel cool when sweat evaporates from our skin?
- Why does a gas exert pressure on the walls of its container?
- Why is the rate of diffusion higher in gases than in liquids?
3. Numerical and Calculation-Based Questions
- Convert the following temperatures:
- 300 K to °C
- 573 K to °C
- 25°C to K
- 373°C to K
- Calculate the mass of a solid substance if its density and volume are given.
- Arrange the following substances in increasing order of density: air, exhaust from chimneys, honey, water, chalk, cotton, and iron.
4. Application-Based Questions
- Why do we sprinkle water on the rooftop in summer?
- Why do we prefer to wear cotton clothes in summer?
- Why does the level of water not increase when salt is dissolved in it?
- How does an increase in temperature affect the rate of diffusion?
5. Comparative Questions
- Differentiate between:
- Solids, Liquids, and Gases
- Boiling and Evaporation
- Diffusion in solids, liquids, and gases
- Compare the movement of particles in different states of matter.
- Compare the kinetic energy of particles in ice, water, and steam.
6. Experimental and Activity-Based Questions
- Explain an experiment to show that matter is made up of particles.
- How can you prove that gases are highly compressible?
- Describe an activity to demonstrate diffusion in liquids.
- Explain an experiment that shows particles of matter have spaces between them.
7. Diagram-Based Questions
- Label and explain the diagram showing the interconversion of states of matter.
- Draw and explain the movement of particles in solids, liquids, and gases.
- Explain the diagram of the experiment showing sublimation of camphor.
8. HOTS (Higher-Order Thinking Skills) Questions
- Why does increasing pressure liquefy gases?
- Why does solid CO₂ (dry ice) change directly into gas without melting into liquid?
- How does pressure affect the boiling point of a liquid?
- Why is steam more dangerous than boiling water?
Solutions for Conceptual Questions
1. What is Matter? Give examples.
Definition-
Matter is anything that occupies space and has mass. Everything in our surroundings, including the air we breathe, the water we drink, and the objects we use daily, is composed of matter.
Characteristics of Matter-
- Matter is made up of tiny particles.
- These particles have space between them.
- The particles of matter are in continuous motion.
- They attract each other due to intermolecular forces.
Examples of Matter-
- Solids- Book, chair, table, ice
- Liquids- Water, milk, juice, oil
- Gases- Air, oxygen, carbon dioxide
Non-matter (Things that do not have mass and volume)-
Emotions (love, hate), thoughts, sound, heat, light, and magnetic forces.
Extra Tip- In exams, provide examples from different states of matter to make your answer more comprehensive.
2. Define the term “diffusion.”
Definition-
Diffusion is the process by which particles of a substance move from a region of higher concentration to a region of lower concentration without any external force.
Explanation-
- Diffusion occurs due to the continuous movement of particles.
- It takes place in solids, liquids, and gases but is fastest in gases due to high kinetic energy.
- The rate of diffusion increases with temperature.
Examples of Diffusion-
- In Gases- The smell of perfume spreads across the room.
- In Liquids- A drop of ink spreads in a glass of water.
- In Solids- If two metal blocks are kept in contact for a long time, their particles intermix at the point of contact.
Exam Tip- To score full marks, include a definition, a brief explanation, and at least two examples.
3. What is the difference between boiling and evaporation?
| Feature | Boiling | Evaporation |
| Definition | The process in which a liquid changes into vapor at its boiling point when heat is applied. | The process in which a liquid changes into vapor at any temperature below its boiling point. |
| Nature | A bulk phenomenon (occurs throughout the liquid). | A surface phenomenon (occurs only at the surface). |
| Temperature | Takes place at a fixed temperature (boiling point). | Occurs at all temperatures. |
| Speed | Rapid process. | Slow process. |
| Example | Water boils at 100°C to form steam. | Clothes dry due to evaporation of water from fabric. |
4. What is sublimation? Give an example.
Definition-
Sublimation is the process in which a solid directly changes into gas without passing through the liquid state. The reverse process (gas to solid) is called deposition.
Explanation-
- Sublimation occurs in substances with weak intermolecular forces.
- This process is used for purifying substances like camphor and iodine.
Examples of Sublimation-
- Camphor
- Naphthalene balls (used in wardrobes to keep clothes fresh)
- Dry ice (solid CO₂)
Exam Tip- Include both the definition and examples for full marks.
5. Define latent heat of fusion and latent heat of vaporization.
Latent Heat of Fusion-
The amount of heat energy required to change 1 kg of a solid into liquid at its melting point without a temperature change is called the latent heat of fusion.
Example- Ice at 0°C melts into water at 0°C, absorbing heat without a rise in temperature.
Latent Heat of Vaporization-
The amount of heat energy required to change 1 kg of a liquid into gas at its boiling point without a temperature change is called the latent heat of vaporization.
Example- Water at 100°C absorbs heat and converts into steam at 100°C without a temperature rise.
Exam Tip- Mention the unit (J/kg) and include an example for a complete answer.
Also Check – 82 Reasoning-Based Questions & Answers-Matter In Our Surroundings -Class 9 Science
Solutions for Reasoning-Based Questions
1. Why does the smell of hot food spread faster than cold food?
Explanation-
- The smell of food is carried by gas particles in the air.
- When food is hot, the kinetic energy of its particles increases.
- Due to higher kinetic energy, the aroma particles move faster and mix quickly with air molecules.
- In contrast, cold food has lower kinetic energy, so the movement of aroma particles is slower.
- The process by which particles mix and spread is called diffusion, and diffusion occurs faster in higher temperatures.
Conclusion-
The smell of hot food spreads faster because of increased kinetic energy, leading to faster diffusion of aroma particles in the air.
2. Why does ice float on water even though it is solid?
Explanation-
- The density of a substance determines whether it floats or sinks.
- Ice is less dense than water because, when water freezes, its molecules arrange themselves in a rigid, open hexagonal structure.
- This structure increases the volume of ice while keeping its mass the same, leading to a decrease in density.
- The density of ice is 0.92 g/cm³, whereas the density of liquid water is 1 g/cm³.
- According to Archimedes’ principle, an object floats if its density is lower than the liquid it is placed in.
Conclusion-
Ice floats on water because its density is lower than that of liquid water due to the expansion of water molecules in a solid state.
3. Why do we feel cool when sweat evaporates from our skin?
Explanation-
- The process of evaporation requires energy in the form of heat.
- When sweat evaporates, it absorbs heat energy from our body and the surroundings.
- This heat is taken away, lowering the temperature of our skin.
- This process is based on the latent heat of vaporization, where water (sweat) absorbs heat to change into vapor.
Conclusion-
We feel cool because evaporation absorbs heat from our body, reducing body temperature and causing a cooling effect.
4. Why does a gas exert pressure on the walls of its container?
Explanation-
- The particles of a gas are in constant random motion due to their high kinetic energy.
- These gas molecules collide with each other and with the walls of the container.
- Every collision exerts a force on the container walls.
- The total force exerted per unit area is called pressure.
- If the number of collisions increases (by increasing temperature or decreasing volume), the pressure increases.
Conclusion-
A gas exerts pressure on the walls of its container because its particles move randomly and collide with the container walls, exerting force.
5. Why is the rate of diffusion higher in gases than in liquids?
Explanation-
- Diffusion occurs when particles move from a region of higher concentration to lower concentration.
- In gases, the particles are far apart, have high kinetic energy, and move randomly at high speeds.
- In liquids, the particles are closer together, have lower kinetic energy, and move more slowly.
- Because gas particles move faster and have less intermolecular attraction, they diffuse more rapidly than liquid particles.
Conclusion-
The rate of diffusion is higher in gases than in liquids because gas particles move faster, have more kinetic energy, and experience weaker intermolecular forces compared to liquids.
Solutions for Numerical and Calculation-Based Questions
1. Convert the following temperatures-
Formula for Conversion-
- Kelvin to Celsius- °C = K – 273
- Celsius to Kelvin- K = °C + 273
Solutions-
a) 300 K to °C
°C = 300 – 273 = 27°C
b) 573 K to °C
°C = 573 – 273 = 300°C
c) 25°C to K
K = 25 + 273 = 298 K
d) 373°C to K
K = 373 + 273 = 646 K
2. Calculate the mass of a solid substance if its density and volume are given.
Formula-
Mass = Density × Volume
Example Calculation-
Let’s assume a solid substance has a density of 5 g/cm³ and a volume of 10 cm³.
Mass = 5 × 10 = 50 g
If the density and volume are different in the question, apply the same formula.
3. Arrange the following substances in increasing order of density-
Given substances-
Air, exhaust from chimneys, honey, water, chalk, cotton, and iron
Approximate Densities-
- Air → 0.0013 g/cm³
- Exhaust from chimneys → Slightly more than air but less than water (~0.0015 g/cm³)
- Cotton → 0.1–0.2 g/cm³ (Low due to trapped air pockets)
- Water → 1 g/cm³
- Honey → ~1.36 g/cm³
- Chalk → ~2.5–2.7 g/cm³
- Iron → 7.8 g/cm³
Increasing Order of Density-
Air < Exhaust from chimneys < Cotton < Water < Honey < Chalk < Iron
Also Check – Chapter 1- Matter In Our Surroundings – Class 9 Science – Long Question and Answers
Solutions for Application-Based Questions
1. Why do we sprinkle water on the rooftop in summer?
Explanation-
- During summer, rooftops absorb a significant amount of heat, making the surroundings hot.
- Water has a high latent heat of vaporization, meaning it absorbs a large amount of heat before it evaporates.
- When water is sprinkled on the rooftop, it absorbs heat from the surface, causing it to evaporate.
- As a result, the temperature of the rooftop decreases, making the surrounding air cooler.
Conclusion-
Sprinkling water on rooftops helps in cooling by utilizing evaporation, which absorbs heat from the surface and lowers the temperature.
2. Why do we prefer to wear cotton clothes in summer?
Explanation-
- In summer, our body perspires to maintain a stable temperature.
- Cotton is a good absorber of sweat, allowing it to soak up moisture from the body.
- The absorbed sweat evaporates quickly, drawing heat away from the body and making us feel cool.
- Evaporation causes cooling, as heat is absorbed from the surroundings during the process.
Conclusion-
Cotton clothes keep us cool by absorbing sweat and allowing faster evaporation, which removes heat from the body.
3. Why does the level of water not increase when salt is dissolved in it?
Explanation-
- Water is made up of tiny particles with spaces between them.
- When salt is added to water, its particles occupy the spaces between water molecules.
- Since salt dissolves within these spaces, it does not cause a noticeable increase in the volume of water.
Conclusion-
The water level does not increase because salt particles fit into the empty spaces between water molecules, rather than adding extra volume.
4. How does an increase in temperature affect the rate of diffusion?
Explanation-
- Diffusion is the process where particles move from a region of higher concentration to lower concentration.
- As temperature increases, the kinetic energy of particles also increases.
- Higher kinetic energy makes particles move faster, causing them to mix more quickly.
- In gases and liquids, the increased movement leads to a higher rate of diffusion.
Example-
- The smell of hot food spreads faster than cold food due to increased diffusion at higher temperatures.
- Ink diffuses more quickly in hot water compared to cold water.
Conclusion-
An increase in temperature increases kinetic energy, leading to faster diffusion of particles.
Also Check – Chapter 1- Matter In Our Surroundings – Class 9 Science – Solved MCQs
Solutions for Comparative Questions
1. Difference between Solids, Liquids, and Gases
| Property | Solids | Liquids | Gases |
| Shape | Fixed | Takes the shape of the container | No fixed shape |
| Volume | Fixed | Fixed | No fixed volume, expands to fill container |
| Compressibility | Negligible | Slightly compressible | Highly compressible |
| Intermolecular Force | Strongest | Moderate | Weakest |
| Intermolecular Spaces | Least | More than solids | Maximum |
| Flow Ability | Cannot flow | Can flow | Can flow and expand freely |
| Example | Ice, wood, metal | Water, milk, oil | Air, oxygen, carbon dioxide |
2. Difference between Boiling and Evaporation
| Feature | Boiling | Evaporation |
| Definition | The process of liquid turning into gas at its boiling point. | The process of liquid turning into gas at any temperature below its boiling point. |
| Nature | Bulk phenomenon (occurs throughout the liquid). | Surface phenomenon (occurs only at the surface). |
| Temperature | Occurs at a fixed temperature (boiling point). | Occurs at all temperatures. |
| Speed | Fast process. | Slow process. |
| Energy Requirement | Requires continuous heat supply. | Occurs naturally without external heat. |
| Example | Water boiling at 100°C. | Clothes drying under the sun. |
3. Difference between Diffusion in Solids, Liquids, and Gases
| State of Matter | Diffusion Rate | Reason |
| Solids | Slowest | Particles are tightly packed, very little movement. |
| Liquids | Moderate | Particles have more space and move freely. |
| Gases | Fastest | Particles are far apart and move rapidly. |
Example-
- Solid- Color slowly spreads in glass when two metals are placed together.
- Liquid- Ink spreads in water.
- Gas- Perfume smell spreads instantly in a room.
4. Comparison of Movement of Particles in Different States of Matter
| State | Particle Movement |
| Solids | Particles vibrate in fixed positions but do not move freely. |
| Liquids | Particles move freely but remain close together. |
| Gases | Particles move randomly at high speed and occupy all available space. |
Conclusion-
The movement of particles increases from solids to liquids to gases due to decreasing intermolecular forces and increasing kinetic energy.
5. Comparison of Kinetic Energy of Particles in Ice, Water, and Steam
| State | Kinetic Energy | Reason |
| Ice (Solid) | Lowest | Particles are tightly packed and only vibrate. |
| Water (Liquid) | Moderate | Particles move more freely but stay close. |
| Steam (Gas) | Highest | Particles move randomly at high speed. |
Conclusion-
As temperature increases, kinetic energy increases because particles move more freely. Steam has the highest kinetic energy, followed by water, and then ice.
Solutions for Experimental and Activity-Based Questions
1. Experiment to Show That Matter is Made Up of Particles
Aim-
To demonstrate that matter is made up of tiny particles.
Materials Required-
- A beaker (100 mL)
- Water
- A spoon
- Sugar or salt
Procedure-
- Fill the beaker halfway with water and mark the water level.
- Add one spoon of sugar or salt to the water.
- Stir the mixture with a spoon until the sugar or salt dissolves.
- Observe the water level in the beaker.
Observation-
- The sugar or salt disappears, indicating that its particles have mixed with water.
- The water level does not rise, showing that sugar/salt particles occupy spaces between water molecules.
Conclusion-
This experiment proves that matter is made up of tiny particles, which can mix with each other without increasing volume.
2. How Can You Prove That Gases Are Highly Compressible?
Aim-
To demonstrate the high compressibility of gases.
Materials Required-
- A syringe
- A rubber stopper (or finger to block the nozzle)
Procedure-
- Take an empty syringe and pull the piston to fill it with air.
- Block the nozzle of the syringe with a rubber stopper or your finger.
- Press the piston slowly and steadily and observe what happens.
Observation-
- The piston moves easily, and air inside the syringe gets compressed.
- The volume of air decreases, proving that gases are highly compressible.
Conclusion-
Gases are highly compressible because their particles are far apart, allowing them to be squeezed closer together when pressure is applied.
3. Activity to Demonstrate Diffusion in Liquids
Aim-
To observe diffusion in liquids.
Materials Required-
- A beaker (100 mL)
- Water
- Ink or potassium permanganate crystals
Procedure-
- Fill a beaker with clear water.
- Add a drop of ink or a few potassium permanganate crystals to the water without stirring.
- Let the setup remain undisturbed and observe the changes.
Observation-
- The ink spreads slowly in the water, turning the entire solution blue or purple.
- After some time, the color is evenly distributed throughout the water.
Conclusion-
This experiment proves that particles of liquids are constantly moving and can mix with other substances due to diffusion.
4. Experiment to Show That Particles of Matter Have Spaces Between Them
Aim-
To demonstrate that particles of matter have spaces between them.
Materials Required-
- A measuring cylinder or a beaker
- Water
- Sugar or salt
Procedure-
- Take 50 mL of water in a beaker or measuring cylinder.
- Add a few teaspoons of sugar or salt to the water.
- Stir the solution until the sugar or salt dissolves completely.
- Check the final water level in the beaker.
Observation-
- The water level does not increase, even though sugar or salt is added.
- This indicates that the particles of sugar or salt occupy the spaces between the water molecules.
Conclusion-
This experiment proves that matter has spaces between its particles, allowing substances to mix without a noticeable increase in volume.
Diagram-Based Questions – Detailed Explanations
1. Label and Explain the Diagram Showing the Interconversion of States of Matter
Diagram-
Explanation-
- Solid to Liquid (Melting/Fusion)- When a solid is heated, its particles gain energy, move apart, and turn into a liquid.
- Liquid to Gas (Evaporation/Vaporization)- On further heating, liquid particles gain more energy, move freely, and become gas.
- Gas to Liquid (Condensation)- When a gas is cooled, it loses energy, and particles come closer, forming a liquid.
- Liquid to Solid (Freezing)- Further cooling causes particles to lose energy and become tightly packed, turning into a solid.
- Solid to Gas (Sublimation)- Some solids change directly into gas without becoming liquid (e.g., camphor, dry ice).
- Gas to Solid (Deposition)- In some cases, gases change directly into solids without passing through the liquid state.
This cycle shows how temperature and pressure affect the states of matter.
2. Draw and Explain the Movement of Particles in Solids, Liquids, and Gases
Diagram-
Explanation-
- Solids-
- Particles are tightly packed in a fixed arrangement.
- They vibrate in their positions but cannot move freely.
- Strong intermolecular forces hold them together.
- Liquids-
- Particles are loosely arranged and can slide past each other.
- They take the shape of the container but have a fixed volume.
- Moderate intermolecular forces allow movement.
- Gases-
- Particles are far apart and move randomly in all directions.
- They fill the entire container and are highly compressible.
- Weak intermolecular forces allow free movement.
This movement explains why solids are rigid, liquids flow, and gases expand to fill their container.
3. Explain the Diagram of the Experiment Showing Sublimation of Camphor
Diagram-
Explanation-
- Materials Required-
- Camphor or naphthalene balls
- China dish
- Inverted funnel
- Cotton plug
- Heat source (burner)
- Procedure-
- Place camphor in a china dish.
- Cover it with an inverted funnel and seal the opening with a cotton plug.
- Apply heat to the dish and observe.
- Observation-
- Camphor directly converts into vapors without turning into liquid.
- The vapors condense at the top of the funnel, forming solid camphor again (deposition).
- Conclusion-
- This experiment proves sublimation, where a solid changes directly into gas without becoming a liquid.
This experiment is used in purification processes and demonstrates the effect of heat on certain substances like camphor, dry ice, and iodine.
HOTS (Higher-Order Thinking Skills) Questions – Detailed Solutions
1. Why does increasing pressure liquefy gases?
Explanation-
- Gases have large intermolecular spaces and weak intermolecular forces.
- When pressure is applied, gas particles come closer, reducing intermolecular space.
- As the particles move closer, intermolecular forces increase, leading to a phase change from gas to liquid.
- At a specific temperature and high pressure, gases condense into liquids (e.g., Liquefied Petroleum Gas (LPG) and Compressed Natural Gas (CNG) are stored under high pressure).
Conclusion-
Increasing pressure reduces the volume of gas and strengthens intermolecular forces, resulting in liquefaction.
2. Why does solid CO₂ (dry ice) change directly into gas without melting into liquid?
Explanation-
- Sublimation is the process where a solid changes directly into gas without passing through the liquid state.
- Carbon dioxide has weak intermolecular forces, and under normal atmospheric pressure, it does not exist as a liquid.
- When dry ice is exposed to atmospheric conditions, it absorbs heat and changes directly into CO₂ gas.
- The surrounding air pressure is not high enough to keep it in liquid form, so it sublimates instead of melting.
Example-
- Dry ice is used in food preservation and stage effects because it sublimates into fog-like CO₂ gas without leaving any liquid residue.
Conclusion-
Solid CO₂ undergoes sublimation instead of melting because it requires extremely high pressure to exist as a liquid.
3. How does pressure affect the boiling point of a liquid?
Explanation-
- Boiling point is the temperature at which the vapor pressure of a liquid equals the atmospheric pressure.
- If pressure increases, the liquid requires more heat energy to form vapors, increasing the boiling point.
- If pressure decreases, the liquid boils at a lower temperature because less energy is needed for vaporization.
Examples-
- High Pressure (Higher Boiling Point)-
- In a pressure cooker, high pressure increases the boiling point of water, allowing food to cook faster.
- Low Pressure (Lower Boiling Point)-
- At high altitudes, atmospheric pressure is lower, so water boils below 100°C, making it difficult to cook food properly.
Conclusion-
Higher pressure increases the boiling point, while lower pressure reduces it, affecting cooking and industrial processes.
4. Why is steam more dangerous than boiling water?
Explanation-
- Boiling water (100°C) and steam (100°C) have the same temperature, but steam contains more energy.
- Latent Heat of Vaporization- Steam carries extra energy absorbed during the phase change from liquid to gas.
- When steam condenses on the skin, it releases this extra energy into the body, causing severe burns.
Example-
- A steam burn is more severe than a hot water burn because steam transfers more heat when it condenses.
Conclusion-
Steam causes more severe burns than boiling water because it has latent heat energy, which is released upon condensation.
