Complete solutions for Class 9 Science Chapter 1: Matter in Our Surroundings | Get detailed answers | GUIDENET

Class 9 Science Chapter 1: Matter in Our Surroundings

Complete NCERT Solutions with Extra Facts and Visual Explanations

Welcome to GUIDENET! In this post, we provide complete solutions for Class 9 Science Chapter 1: Matter in Our Surroundings. We’ve included detailed answers to all NCERT questions, extra facts to spark your interest, and visually stunning explanations to make learning fun and engaging.

Key Topics Covered

• Physical Nature of Matter
• States of Matter: Solid, Liquid, Gas
• Change of State: Melting, Boiling, Sublimation
• Evaporation and Factors Affecting It

NCERT Solutions

Question 1: Which of the following are matter?

Answer: Matter is anything that occupies space and has mass. From the given options:

• Matter: Chair, air, almonds, lemon water, smell of perfume.
• Not Matter: Love, hate, thought, cold (these are emotions or sensations).

Question 2: Why does the smell of hot sizzling food reach you several metres away, but to get the smell from cold food you have to go close?

Answer: The smell of hot sizzling food reaches us faster because:

• Particles in hot food have higher kinetic energy, so they diffuse faster into the air.
• In cold food, particles have less energy, so they diffuse slowly and don’t travel far.

Question 3: A diver is able to cut through water in a swimming pool. Which property of matter does this observation show?

Answer: This shows that particles of matter have space between them. The diver can move through water because the particles of water are not tightly packed and have enough space to allow movement.

Question 4: What are the characteristics of the particles of matter?

Answer:

• Particles have space between them.
• Particles are in continuous motion.
• Particles attract each other with varying force depending on the state of matter.

Question 5: The mass per unit volume of a substance is called density. Arrange the following in order of increasing density – air, exhaust from chimneys, honey, water, chalk, cotton, and iron.

Answer: The order of increasing density is:

1. Air
2. Exhaust from chimneys
3. Cotton
4. Water
5. Honey
6. Chalk
7. Iron

Question 6: (a) Tabulate the differences in the characteristics of states of matter. (b) Comment upon the following: rigidity, compressibility, fluidity, filling a gas container, shape, kinetic energy, and density.

Answer:

(a) Differences in the characteristics of states of matter:

Property	Solid	Liquid	Gas
Shape	Definite	Indefinite	Indefinite
Volume	Definite	Definite	Indefinite
Compressibility	Negligible	Low	High
Kinetic Energy	Low	Moderate	High

(b) Comments:

• Rigidity: Solids are rigid due to strong intermolecular forces.
• Compressibility: Gases are highly compressible, while solids and liquids are not.
• Fluidity: Liquids and gases can flow, but solids cannot.
• Filling a Gas Container: Gases completely fill the container due to free-moving particles.
• Shape: Solids have a fixed shape, while liquids and gases take the container's shape.
• Kinetic Energy: Gases have the highest kinetic energy, while solids have the lowest.
• Density: Solids are generally denser than liquids and gases.

Question 7: Give reasons:

• (a) A gas fills completely the vessel in which it is kept.
  Answer: Gas particles move freely and occupy all available space.
• (b) A gas exerts pressure on the walls of the container.
  Answer: Gas particles collide with container walls, exerting pressure.
• (c) A wooden table should be called a solid.
  Answer: It has a fixed shape, volume, and is rigid.
• (d) We can easily move our hand in air but to do the same through a solid block of wood we need a karate expert.
  Answer: Solid particles are tightly packed, while gas particles have more space.

Question 8: Liquids generally have lower density as compared to solids. But you must have observed that ice floats on water. Find out why.

Answer: Ice floats on water because it has a lower density than liquid water. This is due to the structure of ice, where water molecules form an open lattice with air spaces, making it less dense than water.

Question 9: Convert the following temperature to Celsius scale:

• (a) 300 K → Answer: 300 - 273 = 27°C
• (b) 573 K → Answer: 573 - 273 = 300°C

Question 10: What is the physical state of water at:

• (a) 250°C → Answer: Gaseous (steam)
• (b) 100°C → Answer: Both liquid and gas (boiling point of water)

Question 11: For any substance, why does the temperature remain constant during the change of state?

Answer: The temperature remains constant because the heat energy supplied is used in breaking the intermolecular forces between particles, rather than increasing the temperature.

Question 12: Suggest a method to liquefy atmospheric gases.

Answer: Atmospheric gases can be liquefied by applying high pressure and reducing the temperature.

Question 13: Why does a desert cooler cool better on a hot dry day?

Answer: A desert cooler works better on a hot dry day because evaporation happens faster in dry air, absorbing more heat and cooling the surroundings.

Question 14: How does the water kept in an earthen pot (matka) become cool during summer?

Answer: The earthen pot has small pores that allow water to evaporate. As water evaporates, it absorbs heat from the pot and cools the remaining water.

Question 15: Why does our palm feel cold when we put some acetone, petrol, or perfume on it?

Answer: These substances evaporate quickly, absorbing heat from our skin, which causes a cooling sensation.

Question 16: Why are we able to sip hot tea or milk faster from a saucer rather than a cup?

Answer: A saucer has a larger surface area, which allows the tea or milk to cool faster due to increased evaporation.

Question 17: What type of clothes should we wear in summer?

Answer: We should wear cotton clothes in summer as they absorb sweat and allow it to evaporate, keeping us cool.

Question 18: Convert the following temperatures to the Celsius scale:

• (a) 293 K → Answer: 293 - 273 = 20°C
• (b) 470 K → Answer: 470 - 273 = 197°C

Question 19: Convert the following temperatures to the Kelvin scale:

• (a) 25°C → Answer: 25 + 273 = 298 K
• (b) 373°C → Answer: 373 + 273 = 646 K

Question 20: Give reason for the following observations:

• (a) Naphthalene balls disappear with time without leaving any solid.
  Answer: Naphthalene undergoes sublimation, turning directly from solid to gas.
• (b) We can get the smell of perfume sitting several metres away.
  Answer: Perfume particles diffuse rapidly in air.

Question 21: Arrange the following substances in increasing order of forces of attraction between the particles— water, sugar, oxygen.

Answer: Oxygen < Water < Sugar

Question 22: What is the physical state of water at—

• (a) 25°C → Answer: Liquid
• (b) 0°C → Answer: Solid (ice) or liquid depending on external pressure
• (c) 100°C → Answer: Liquid and gas (boiling point of water)

Question 23: Why is ice at 273 K more effective in cooling than water at the same temperature?

Answer: Ice at 273 K absorbs latent heat from the surroundings to convert into water, thus providing additional cooling.

Question 24: What produces more severe burns, boiling water or steam?

Answer: Steam causes more severe burns than boiling water because it has additional latent heat of vaporization.

Question 25: Name A, B, C, D, E, and F in the following diagram showing change in its state:

Answer: The diagram refers to different states of matter and their changes.

• A: Solid
• B: Liquid
• C: Gas
• D: Melting (Solid to Liquid)
• E: Evaporation (Liquid to Gas)
• F: Condensation (Gas to Liquid)

Additional One-Mark Questions for Practice

• Q1: What is the SI unit of mass?
  Answer: Kilogram (kg)
• Q2: What is the boiling point of water in Kelvin?
  Answer: 373 K
• Q3: Which state of matter has the highest kinetic energy?
  Answer: Gas
• Q4: What is the process of conversion of gas to liquid called?
  Answer: Condensation
• Q5: What is the chemical formula of water?
  Answer: H₂O
• Q6: Which force holds the particles together in a solid?
  Answer: Intermolecular force of attraction
• Q7: What is the SI unit of temperature?
  Answer: Kelvin (K)
• Q8: What is sublimation?
  Answer: Direct conversion of solid to gas without becoming liquid
• Q9: Name one substance that undergoes sublimation.
  Answer: Naphthalene
• Q10: Which process converts liquid into gas at any temperature below its boiling point?
  Answer: Evaporation
• Q11: What is the melting point of ice in Kelvin?
  Answer: 273 K
• Q12: What happens to the temperature during a phase change?
  Answer: It remains constant
• Q13: What is diffusion?
  Answer: The spontaneous mixing of particles of two substances
• Q14: Which state of matter has a definite shape and volume?
  Answer: Solid
• Q15: What is latent heat?
  Answer: The heat energy required to change the state of a substance without a change in temperature
• Q16: What type of intermolecular forces are strongest – solids, liquids, or gases?
  Answer: Solids
• Q17: What is the SI unit of pressure?
  Answer: Pascal (Pa)
• Q18: What is the term for the change of a liquid into solid?
  Answer: Freezing
• Q19: What is the term for the change of a gas into a solid?
  Answer: Deposition
• Q20: Why do gases expand to fill any container?
  Answer: Because gas particles move freely and have high kinetic energy

We hope this post helped you understand Chapter 1: Matter in Our Surroundings in a fun and engaging way. For more chapters and subjects, visit GUIDENET!