Matter in Our Surrounding
Class: 9 | Chapter: 1
NCERT Intext Questions & Answer
1. Which of the following are matter ?Chair, air, love, smell, hate, almonds, thought, cold, cold-drink, smell of perfume.
Answer: Chair, air, almonds and cold drink.
2. Give reasons for the following observation:
The smell of hot sizzling food reaches you several meters away, but to get the smell from cold food you have to go close.
Answer: Diffusion has a direct relationship with rise of temperature. So, when the food is hot, the smell mixes with air particles and spread easily. But when food is at low temperature (cold), we need to go close to get the smell.
3. A diver is able to cut through water in a swimming pool. Which property of matter does this observation show ?
Answer: Water has week forces of attraction between it's molecules. So, it is offering minimum resistance to the diver's body.
4. What are the characteristics of the particles of matter?
Answer: 1. Particles of matters are very small in size.
2. Particles of matter have space between them.
3. Particles of matter are continuously moving.
4. Particles of matter attract each other.
5. 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: The increasing order of density : Exhaust from chimneys < air < water < honey < cotton < chalk < iron.
6.(a) Tabulate the differences in the characteristics of states of matter.
Answer: Characteristics of Solid, Liquid and Gas-
| Characteristics | Solid | Liquid | Gas |
|---|---|---|---|
| Shape & volume | Fixed shape & volume | Fixed volume but no fixed shape | Neither a fixed shape nor a fixed volume |
| Intermopecular Space | Minimum | Intermediate | Maximum |
| Intermolecular forces | Strongest | Less Strong | Negligible |
| Kinetic Energy | Minimum | More than Solids | Maximum |
(b) Comment upon the following: rigidity, compressibility, fluidity, filling a gas container, shape, kinetic energy and density.
Answer: Rigidity: Solids are rigid means they have fixed shape because of close packing and strong forces of attraction between particles.
Compressibility: Solids and liquids are not much compressible. Gases can be easily compressed.
Fluidity: Fluidity means tendency to flow. Solids don't flow. Liquids and gases flow easily.
Filling a gas container: Solids and liquids have more interparticle forces of attraction that's why they don't fill their container completely. But a gas due to negligible interparticle attraction fills its container completely.
Shape: Solids have fixed shape. Liduids and gases take the shape of the vessels in which they are kept.
Kinetic energy: Solids have minimum kinetic energy, liquids have more than solids and gases have maximum kinetic energy.
Density: Solids have highest density, less in liquids and minimum in gases.
7. Give reasons:
(a) A gas fills completely the vessel in which it is kept.
Answer: Gas molecules can move in all directions with high speeds due to high kinetic energy and less forces of attraction. In this way gases fill the container completely in which they are kept.
(b) A gas exerts pressure on the walls of the container.
Answer: While moving, gas particles hit each other and also the walls of the container. Due to this hitting( collision) gas particles exert pressure on the walls of the container. Pressure = Force exerted per unit area on the walls of the container.
(c) A wooden table should be called a solid.
Answer: A wooden table should be called a solid because it had fixed shape and volume moreover it is not compressible.
(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: This is due to the difference in amount of intermolecular forces of attraction between solids and gases. Gases have least forces so it's easy to move our hand in air but for solid wooden block forces are strongest.
8. Liquids generally have lower density as compared to solids. But you must have observed that ice floats on water. Find out why ?
Answer: Density of ice is less than water that's why ice floats on water.
9. Convert the following temperature to Celsius scale:
(a) 300 K (b) 573 K.
Answer: Temperature on celsius scale = Temperature on kelvin scale - 273
(a) 300 - 273 = 27°C
(b) 573 - 273 = 300°C
10. What is the physical state of water at:
(a) 250°C (b) 100°C
Answer: (a) liquid (b) gas
11. For any substance, why does the temperature remain constant during the change of state ?
Answer: It is because of latent heat ( hidden heat) which gets used up in changing the state by overcoming the forces of attraction between the molecules.
12. Suggest a method to liquefy atmospheric gases ?
Answer: 1. By reducing temperature
2. By applying pressure
13. Why does a desert cooler cool better on a hot dry day ?
Answer: On a hot dry day, Temperature will be high and humidity will be less. Both factors will increase the rate of evaporation.Evaporation cools the pads and circulates water. Thus, a desert cooler cools better on a hot dry day.
14. How does the water kept in an earthen pot (matka) become cool during summer ?
Answer: Earthen pot has small pores on its surface. Water comes out through these pores and changes into vapour by absorption of heat from the water inside the earthen pot. Thus the water inside the pot becomes cool.
15. Why does our palm feel cold when we put some acetone or petrol or perfume on it ?
Answer: Acetone , petrol and perfumes are volatile liquids. They get easily vapourised by taking energy from our palm and evaporate . After loosing energy ( heat) our palm feels cold.
16. Why are we able to sip hot tea or milk faster from a saucer rather than a cup ?
Answer: Rate of evaporation depends upon surface area. More is the surface area, higher will be rate of evaporation. Saucer has more surface area than a cup and more cooling will be done. Hence we able to sip hot tea or milk faster from a saucer rather than a cup.
17. What type of clothes should we wear in summer ?
Answer: We should wear light colored cotton clothes in summer. During summer we perspire a lot. Cotton, being a good absorber of water helps in absorbing the sweat from body and exposing it to the atmosphere for easy evaporation.
NCERT Exercise Questions & Answer
1. Convert the following temperatures to the Celsius scale.(a)300K (b) 573K.
Answer: Temperature on kelvin scale = Temperature on Celsius scale + 273
K = C + 273
(a) 300 = C + 273
C = 300-273
C = 27°C
(b) 573 = C + 273
C = 573 - 273
C = 300° C
2. Convert the following temperatures to the Kelvin scale.
(a) 25°C (b) 373°C.
Answer: As we know, K = C + 273
(a) K = 25 + 273
K = 298
(b) K = 373 + 273
K = 646
3. Give reason for the following observations.
(a) Naphthalene balls disappear with time without leaving any solid.
Answer: It is due to sublimation . Here naphthalene balls directly change from solid state to gaseous state.
(b) We can get the smell of perfume sitting several metres away.
Answer: Perfumes are volatile liquids, they can quickly changes into vapours. Due to gaseous nature, they have high kinetic energy and rate of diffusion. In this way particles of perfume mix with the particles of air and soread out. Hence we are able to get the smell of perfume sitting several metres ways.
4. Arrange the following substances in increasing order of forces of attraction between the particles—water, sugar, oxygen.
Answer: Sugar > water > oxygen
5. What is the physical state of water at:
(a) 25°C (bj 0°C (cj 100°C
Answer: (a) liquid
(b) solid
(c) gas
6. Give two reasons to justify
(a) water at room temperature is a liquid.
Answer: Physical state depends on molecular structure. Water has special type of Hydrogen bonds in its molecule. Due to this , it shows characteristics of liquids like it has definite volume but not definite shape like other liquids and it takes the shape of the container in which it is kept. Therefore, water at room temperature is a liquid.
(b) An iron almirah is a solid at room temperature.
Answer: Iron has definite shape & volume. It is incompressible, rigid , high melting and boiling point. All these properties are of solid state. Hence an iron almirah is a solid at room temperature.
7 . Why is ice at 273 K more effective in cooling than water at the same temperature ?
Answer: Cooling takes place when heat is removed from a system. In case of ice at 273 K, it will take latent heat from the medium to convert itself into water at 273 K and then into water at a higher temperature. Water does not absorb any extra heat from the substance. Thus, ice is more effective in cooling than water at 273 K.
8. Which produces more severe burns, boiling water or steam ?
Answer: Steam will produce more severe burns than boiling water.
9. Name A, B, C, D, E and F in the following diagram showing change in its state:
Answer: A : Fusion
B : Evaporation
C : Condensation
D : Freezing
E : Sublimation
F : Desublimation / Sublimation