Chapter 1 . Matter in Our Surroundings

Class 9 Science Chapter 1 Matter in Our Surroundings Internal Questions and Answers :

1. Which of the following are matter?
Chair, air, love, smell, hate, almonds, thought, cold, lemon water, smell of perfume.

Answer : The items that are considered matter are chair, air, almonds, cold, lemon water, and the smell of perfume. Love, smell, hate, and thought are not considered matter as they do not have mass or occupy physical space.

2. Give reasons for the following observation:
The smell of hot sizzling food reaches you several metres away, but to get the smell from cold food you have to go close.

Answer : The smell from hot sizzling food can travel far because its tiny particles move around quickly due to the heat, reaching us from a distance. Cold food doesn't release as many particles, and they move slower, so we have to get closer to smell it.

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

Answer : This observation shows that particles of matter have space between them. The diver can move through the water because there is space between water molecules, allowing the diver to cut through it.

4. What are the characteristics of the particles of matter?

Answer: the characteristics of the particles of matter are

(i) Particles of matter have space between them .

(ii) Particles of matter are continuously moving .

(iii) Particles of matter attract each other .

Internal Questions :

1. The mass per unit volume of a substance is called density. (density = mass/volume).Arrange the following in order of increasing density – air, exhaust from chimneys, honey, water, chalk, cotton and iron.

Answer:  Arranging the substances in order of increasing density:

Air < Cotton < Chalk < Water < Honey < Exhaust from chimneys < Iron

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

Answer: (a) Tabulated differences in characteristics of states of matter:

Characteristics	Solid	Liquid	Gas
Rigidity	High	Moderate	Low
Compressibility	Low	Moderate	High
Fluidity	No	Yes	Yes
Filling a gas container	No	No	Yes
Shape	Definite	No	Indefinite
Indefinite Kinetic Energy	Low	Moderate	High
Density	High	Moderate	Low

 (b) Comment on the following:
(i) Solids are difficult to change their shape and may break under force; this property is called rigidity.

 (ii) Compressibility is the ability of a substance, like a gas, to be compressed into a smaller volume under pressure. Gases are highly compressible due to the space between their particles.

 (ii) Liquids flow, change shape, and are not rigid; this property is called fluidity.

(iii) Filling a gas container means that gases spread and occupy the entire available space in the container, conforming to its shape. Gases have no fixed volume or shape.

(iv) Solids tend to maintain their shape when subjected to outside forces.

(v) Kinetic energy is the energy of motion. All matter, including particles in solids, liquids, and gases, has kinetic energy. It increases with higher temperatures, making particles move faster.

(vi) Density is a measure of how tightly matter is packed into a given space .

3. Give reasons
(a) A gas fills completely the vessel in which it is kept.
(b) A gas exerts pressure on the walls of the container.
(c) A wooden table should be called a solid.
(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: (a) A gas fills completely because its particles are tiny and move fast, spreading out to occupy all available space.

(b) Gas particles move randomly and hit container walls, causing pressure.

(c) A wooden table is solid because it keeps its shape and has tightly packed particles.

(d) Air has widely spaced particles, making it easy to move through, while wood is dense and needs force to pass through.

4. 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 its density is lower than that of liquid water. When water freezes, it forms a crystalline structure with more space between molecules, making it less dense and causing it to float.

Internal Questions :

1. Convert the following temperature to celsius scale:
a. 300 K b. 573 K.

Answer : (a) We have,  300 K  –  273.15 = 26.85°C

Therefore, 300 K is equivalent to 26.85°C.

(b) We have, 573 K  –  273.15 = 299.85°C

Therefore, 573 K is equivalent to 299.85°C.

2. What is the physical state of water at:
a. 250ºC b. 100ºC ?

Answers : (a) At 250°C, water is in the gaseous state. It exists as steam or water vapor. The boiling point of water is 100°C, and at 250°C, water is well above its boiling point, causing it to be in the form of a gas.

(b) At 100°C, water is in the liquid state. This is the boiling point of water at standard atmospheric pressure. Water reaches its boiling point and undergoes a phase change from a liquid to a gas (steam) at this temperature.

3. For any substance, why does the temperature remain constant during the change of state?

Answers : The temperature remains constant during a change of state because the heat energy is used to overcome the latent heat of fusion (melting) or vaporization (boiling), causing a phase change rather than a temperature increase.

4. Suggest a method to liquefy atmospheric gases.

Answers : One method to liquefy atmospheric gases is applying pressure and reducing temperature .

This process is commonly used in liquefied natural gas (LNG) production and other applications where atmospheric gases like nitrogen and oxygen need to be liquefied.

Internal Questions :

1. Why does a desert cooler cool better on a hot dry day?

Answers : A desert cooler cools better on a hot dry day because dry air can absorb more water vapor. The cooler uses evaporation to cool air, and dry conditions allow for faster and more effective evaporation, resulting in better cooling.

2. How does the water kept in an earthen pot (matka) become cool during summer?

Answers : Water in an earthen pot cools in summer due to evaporation. The pot's (matka) absorbent surface allows water to evaporate, removing heat from the pot (matka), which makes the water inside cooler.

3. Why does our palm feel cold when we put some acetone or petrol or perfume on it?

Answers : Our palm feels cold when we put acetone, petrol, or perfume on it because these substances quickly evaporate, taking heat energy from our skin in the process, which makes our skin feel cold.

4. Why are we able to sip hot tea or milk faster from a saucer rather than a cup?

Answers : We can sip hot tea or milk faster from a saucer than a cup because the larger surface area of the saucer allows for faster evaporation of the liquid's heat, making it cool quicker for drinking.

5. What type of clothes should we wear in summer?

Answers : In summer, wear light and breathable clothes made of materials like cotton. These clothes allow sweat to evaporate quickly, cooling the body by promoting efficient evaporation and heat dissipation (loss).

Class 9 Science Chapter 1 Matter in ours Surroundings Exercise Questions and Answers

1. Convert the following temperatures to the celsius scale.
(a) 293 K (b) 470 K

Answer : (a) We have, 293 K  – 273.15 = 19.85°C              

Therefore, 293 K is equivalent to 19.85°C.

(b) We have, 470 K  –  273.15 = 196.85°C

Therefore, 470 K is equivalent to 196.85°C.

2. Convert the following temperatures to the kelvin scale.
(a) 25°C (b) 373°C

Answer : (a) We have,  25°C + 273.15 = 298.15 K

Therefore, 25°C is equivalent to 298.15 K.

(b) We have, 373°C + 273.15 = 646.15 K

Therefore, 373°C is equivalent to 646.15 K.

3. Give reason for the following observations.
(a) Naphthalene balls disappear with time without leaving any solid.
(b) We can get the smell of perfume sitting several metres away.

Answer : (a) Naphthalene balls disappear without leaving any solid because they undergo sublimation, which is the process where a substance changes directly from a solid to a gas without going through the liquid phase.

(b) We can smell perfume from a distance because perfume molecules are volatile and can evaporate into the air. These molecules move through the air and reach our nose, allowing us to detect the scent even when sitting several meters away.

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

Answer : We have,  Oxygen < Water < Sugar

5. What is the physical state of water at—
(a) 25°C (b) 0°C (c) 100°C ?

Answers :  (a) At 25°C, water is typically in a liquid state. It is within the temperature range at which water commonly exists as a liquid.

(b) At 0°C, water undergoes a phase change and transitions from a liquid to a solid state. It freezes and becomes ice. The melting point of water is precisely 0°C (32°F), so at this temperature, water exists as a solid.

(c) At 100°C, water undergoes another phase change and transitions from a liquid to a gaseous state. It boils and becomes steam. The boiling point of water is precisely 100°C (212°F), so at this temperature, water exists as a gas.

6. Give two reasons to justify—
(a) water at room temperature is a liquid.
(b) an iron almirah is a solid at room temperature.

Answers :  (a) Water is a liquid at room temperature because its melting point is 0°C (32°F), which is above the room temperatures, and its boiling point is 100°C (212°F).

(b) An iron almirah is a solid at room temperature because iron's melting point and boiling point are higher than room temperatures.

7. Why is ice at 273 K more effective in cooling than water at the same temperature?

Answers : Ice at 273 K is more effective in cooling than water at the same temperature because it absorbs a greater amount of heat energy from the surroundings during the phase change from solid to liquid, providing a stronger cooling effect.

8. What produces more severe burns, boiling water or steam?

Answers : Steam produces more severe burns than boiling water because it not only carries heat at 100°C but also releases additional heat during the condensation process due to its high latent heat of vaporisation.

9. Name A,B,C,D,E and F in the following diagram showing change in its state  

Answers :  A --- Fusion or melting .

B ---- Evaporation .

C---- Condensation .

D---- Solidification .

E---- Sublimation .

F---- Solidification .