CBSE Class 9 Science Exemplar Chapter 1: Matter in Our Surroundings NCERT Solutions
This comprehensive set of NCERT Solutions for CBSE Class 9 Science Exemplar, Chapter 1, 'Matter in Our Surroundings,' delves into the fundamental properties of matter. The solutions explain key concepts such as diffusion, evaporation, and the expansion of gases with increasing temperature. They also clarify the conditions required for liquefying gases, the characteristic property of fluids, and the scientific principle behind water cooling in earthen pots. By providing clear, step-by-step explanations and elaborating on the underlying scientific phenomena, these solutions aim to enhance students' understanding and aid in effective exam revision for the chapter.
Quick info
| Board | CBSE |
|---|---|
| Class | Class 9 |
| Subject | Science Exemplar |
| Session | 2026 |
| Language | English |
| Type | NCERT Solutions |
| Chapter | Chapter 1 |
Chapter summary
Chapter 1 of the CBSE Class 9 Science Exemplar, 'Matter in Our Surroundings,' focuses on the basic states of matter and their properties. The NCERT Solutions cover multiple-choice questions that test understanding of diffusion, evaporation, gas liquefaction, the fluid nature of gases and liquids, and the cooling effect of evaporation. The solutions provide detailed explanations for each concept, reinforcing learning.
Learning outcomes
- Understand the effect of temperature on diffusion, evaporation, and gas expansion.
- Identify the conditions necessary for liquefying gases.
- Differentiate between fluids and other states of matter.
- Explain the phenomenon of evaporation and its cooling effect.
- Compare the forces of attraction between particles in different substances.
Topics covered
Paper topics
- States of Matter
- Properties of Matter
- Diffusion
- Evaporation
- Temperature Effects
- Pressure Effects
- Gas Liquefaction
- Fluids
- Forces of Attraction
Important topics
- Diffusion and Evaporation
- Conditions for Gas Liquefaction
- Fluidity of Gases and Liquids
- Cooling Effect of Evaporation
- Inter-particle Forces
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Questions and Solutions
Multiple Choice Questions
(a) Diffusion, evaporation, compression of gases
(b) Evaporation, compression of gases, solubility
(c) Evaporation, diffusion, expansion of gases
(d) Evaporation, solubility, diffusion, compression of gases
The correct answer is (c) Evaporation, diffusion, and expansion of gases.
Explanation:
Particles within matter are in constant motion, possessing kinetic energy. When the temperature is increased, this kinetic energy rises, leading to several effects:
- Diffusion: Increased particle motion causes them to intermix more readily, which is the process of diffusion.
- Evaporation: Raising the temperature provides more energy for liquid molecules to overcome intermolecular forces and escape into the gaseous phase as vapours.
- Expansion of Gases: Higher temperatures cause gas molecules to move faster and collide more forcefully with container walls, leading to an increase in volume or pressure, hence expansion.
Compression of gases typically requires increased pressure, not necessarily increased temperature, and solubility can be affected by temperature in various ways depending on the solute and solvent.
Multiple Choice Questions
(a) Low temperature, low pressure
(b) High temperature, low pressure
(c) Low temperature, high pressure
(d) High temperature, high pressure
The correct set of conditions is (c) Low temperature, high pressure.
Explanation:
To convert a gas into a liquid, the particles need to be brought closer together and their kinetic energy reduced. This is achieved by:
- High Pressure: Applying significant pressure forces the gas molecules closer to each other, overcoming the large intermolecular spaces present in the gaseous state.
- Low Temperature: Cooling the gas reduces the kinetic energy of its molecules. This allows the attractive forces between the molecules to become significant enough to hold them together in the liquid state.
When a gas is compressed, heat is generated. Therefore, cooling is essential to remove this heat and facilitate liquefaction.
Multiple Choice Questions
(a) Only gases behave like fluids
(b) Gases and solids behave like fluids
(c) Gases and liquids behave like fluids
(d) Only liquids are fluids
The correct statement is (c) Gases and liquids behave like fluids.
Explanation:
A fluid is defined as a substance that has the ability to flow and change its shape easily. This property is characteristic of both gases and liquids. In these states of matter, the intermolecular forces of attraction between particles are weaker compared to solids. This allows the particles to move past one another, enabling the substance to flow and take the shape of its container.
Solids, on the other hand, have strong intermolecular forces that hold their particles in fixed positions, preventing them from flowing.
Multiple Choice Questions
(a) diffusion
(b) transpiration
(c) osmosis
(d) evaporation
The phenomenon responsible for the cooling of water in an earthen pot is (d) evaporation.
Explanation:
Earthen pots are porous, meaning they have tiny holes. Water seeps through these pores to the outer surface of the pot. From this surface, the water evaporates into the surrounding air. Evaporation is a process that requires energy, specifically heat energy. The heat required for this evaporation is absorbed from the water remaining inside the pot and the pot itself. This removal of heat causes the temperature of the water inside to decrease, making it feel cool.
Other terms mentioned:
- Transpiration: The process of water movement through plants and its evaporation from aerial parts, such as leaves, stems, and flowers.
- Diffusion: The movement of particles from an area of higher concentration to an area of lower concentration.
- Osmosis: The movement of solvent molecules through a selectively permeable membrane from a region of lower solute concentration to a region of higher solute concentration.
Multiple Choice Questions
(a) Water, air, wind
(b) Air, sugar, oil
(c) Oxygen, water, sugar
(d) Salt, juice, air
The correct arrangement representing the increasing order of forces of attraction between particles is (c) Oxygen, water, sugar.
Explanation:
The strength of forces of attraction between particles varies significantly across the different states of matter:
- Gases (like Oxygen): Have very weak forces of attraction between particles. The particles are far apart and move randomly.
- Liquids (like Water): Have intermediate forces of attraction. The particles are closer than in gases but can still move past each other, allowing liquids to flow.
- Solids (like Sugar): Have strong forces of attraction between particles. The particles are held in fixed positions, giving solids a definite shape and volume.
Therefore, the order of increasing forces of attraction is Oxygen (gas) < Water (liquid) < Sugar (solid).
Common mistakes
- Confusing the conditions for gas liquefaction (low temp, high pressure).
- Incorrectly identifying which states of matter exhibit fluid behavior.
- Misunderstanding the scientific principle behind water cooling in earthen pots.
- Confusing diffusion with other processes like osmosis or transpiration.
Revision tips
- Review the definitions and examples of diffusion and evaporation.
- Memorize the conditions required to liquefy gases.
- Understand why liquids and gases are classified as fluids.
- Relate the concept of evaporation to everyday phenomena like cooling in earthen pots.
Practice MCQs
Q1. Which of the following sets of phenomena will increase when the temperature is raised?
Explanation: Increasing temperature increases the kinetic energy of particles, leading to faster movement. This enhances diffusion (intermixing of particles), evaporation (conversion of liquid to gas), and expansion of gases as particles move further apart.
Q2. To liquefy a gas, what specific conditions of temperature and pressure are required?
Explanation: Liquefying a gas requires bringing its particles closer together (high pressure) and reducing their kinetic energy (low temperature) so that intermolecular forces can hold them in a liquid state.
Q3. Which statement correctly describes the property of flowing, unique to fluids?
Explanation: Fluids are substances that can flow. Both gases and liquids possess the ability to flow because the intermolecular forces between their particles are relatively weak, allowing them to move past each other.
Q4. During summer, water kept in an earthen pot becomes cool primarily due to which phenomenon?
Explanation: Earthen pots have small pores through which water seeps out and evaporates. This evaporation process requires heat energy, which it draws from the water inside, thus cooling the water.
Q5. Which of the following represents the correct increasing order of 'forces of attraction' between particles?
Explanation: The forces of attraction between particles are strongest in solids, intermediate in liquids, and weakest in gases. Sugar (solid) has the strongest forces, water (liquid) has intermediate forces, and oxygen (gas) has the weakest forces.
Frequently asked questions
What are the key concepts covered in CBSE Class 9 Science Exemplar Chapter 1?
Chapter 1 covers the fundamental concepts of matter, including its states, properties, diffusion, evaporation, the effect of temperature and pressure on states of matter, and the phenomenon of fluid behavior.
How do these NCERT Solutions help with exam preparation?
These solutions provide detailed explanations for each question, clarifying complex concepts and offering step-by-step reasoning. This helps students understand the 'why' behind the answers, improving their grasp of the subject for exams.
What conditions are needed to liquefy a gas?
To liquefy a gas, one needs to apply high pressure and maintain a low temperature. High pressure brings the gas particles closer, while low temperature reduces their kinetic energy, allowing intermolecular forces to dominate and form a liquid.
Why does water kept in an earthen pot feel cool?
Water kept in an earthen pot feels cool due to evaporation. The porous nature of the pot allows water to seep through and evaporate from the outer surface. This evaporation process uses heat energy from the water inside, thus cooling it.
Are gases considered fluids?
Yes, both gases and liquids are considered fluids. This is because they have the ability to flow, a property attributed to the relatively weak forces of attraction between their particles, allowing them to move freely.
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