Class 9 Science

Chapter 1- Matter In Our Surroundings

Questions

Page No.03

1. Which of the following are matter ?

Chair, air, love, smell, hate, almonds, thought, cold, cold-drink, smell of perfume.

Ans: The following substances are matter –

Chair, Air, Almonds, cold-drink,Smell of perfume.

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.

Ans: Particles in the air, if given with higher temperatures, acquire high kinetic energy which aids them to move fast over a stretch. Hence, the smell of hot sizzling food reaches a person even at a distance.

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

Ans: The diver is able to easily cut through the water in the swimming pool because of weak forces of attraction between water molecules. Due to this property of water, a diver is able to cut through water in a swimming pool.

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

Ans: The characteristics of the particles of matter are as follows –

(i) Particles of matter have space between them.

(ii) They are continuously moving.

(iii) They attract each other.

Questions

Page No.06

1. The mass per unit volume of a substance is called density.

(density = mass/volume).

Arrange the following in the order of increasing density –

air, exhaust from chimneys, honey, water, chalk, cotton and iron.

Ans: The following substances are arranged in the increasing density –

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

2. (a) Tabulate the differences in the characteristics of matter.

    (b) Comment upon the following:

    Rigidity, compressibility, fluidity, filling a gas container, shape, kinetic energy and density.

Ans: (a) The differences in the characteristics of three states of matter are as follows –

Characteristics           Solid               Liquid                Gas

(i) Shape               Fixed shape   No fixed shape    No fixed shape

(ii) Volume           Fixed volume

(iii) Intermolecular   Maximum   less than solids    very less

Force

(iv) Intermolecular   Very less   More than solids   Maximum

Space

(v) Rigidity            Rigid               Not rigid                 Not rigid

(vi) Fluidity        Can not flow      Can flow         Can flow

(vii) Compressibility   Negligible    Compressible      Highly compressible

(b) (i) Rigidity: It is the property of matter to continue to remain in its shape when applied with an external force.

(ii) Compressibility: It is the attribute of the particles to contract its intermolecular space when exposed to an external force thereby escalating its density.

(iii) Fluidity: It is the ability of a substance to follow or move about freely.

(iv) Filling a gas container: The particles in a container take its shape as they randomly vibrate in all possible directions.

(v) Shape: It is the definite structure of an object within an external boundary.

(vi) Kinetic energy: The energy possessed by the particles due to their motion is called kinetic energy.

(vii) Density: The mass per unit volume of a substance is called density.

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 the air but to do the same through a solid block of wood we need a karate expert.

Ans: (a) There is a low force of attraction between gas particles and they have high kinetic energy due to which they keep moving in all directions. That is why gas fills completely the vessel in which it is kept.

(b) A gas exerts pressure on the walls of the container because the molecules of the gas are in constant random motion due to high kinetic energy. These molecules constantly vibrate, move and hit the walls of the container thereby exerting pressure on it.

(c) The particles of wooden table are tightly packed with each other, there is no intermolecular space, it cannot be compressed, it cannot flow, all these are characteristics of solid. So wooden table should be called a solid.

(d) The molecules of air have less force of attraction between them and maximum intermolecular space. But in case of solids, the molecules have maximum force of attraction, very less intermolecular space and the particles are tightly bound due to this force. That is why we can easily move our hand in the air but to do the same through a solid block of wood we need a karate expert.

4. Liquids generally have a lower density than solids. But you must have observed that ice floats on water. Find out why?

Ans: Ice is a solid but its density is lower than water due to its structure. The molecules in ice make a cage like structure with lot of vacant spaces. That is why ice float on water.

Questions

Page No.09

1. Convert the following temperature to celsius scale.

(a) 300K                                                           (b) 573K

Ans: 300K = (300 – 273)°C = 27°C       Ans: 573K = (573 – 273)°C = 300°C

2.What is the physical state of water at:

(a) 250°C                  (b) 100°C

Ans: (a) At 250°C, water is in gaseous state.

(b) At 100°C, water is in both liquid and gaseous state.

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

Ans:During the change of state of any matter heat is supplied to the substance. The molecules of this matter use heat to overcome the force of attraction between the particles, at this period of time, temperature remains constant. This extra heat is acquired by the molecules in the form of hidden heat called latent heat to change from one state of matter to the other state.

4. Suggest a method to liquefy atmospheric gases?
Ans:The atmospheric gases are taken in a cylinder with piston fitted on it. By increasing the pressure and decreasing the temperature, the gases can be liquefied.

Questions

Page No.10

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

Ans:It is because the temperature is high and it is less humid on a hot dry day which enables better evaporation. High levels of this evaporation provide better cooling effects.

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

Ans: The earthen pot is porous with lot of pores on it, the water drains out through these tiny pores and the water gets evaporated at the surface of the pot thereby causing cooling effect. This makes the pot cold and the water inside the pot cools by this process.

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

Ans: Acetone, petrol or perfume are volatile substances. When they come into contact with our palm, they absorb heat from our palm and get evaporated. That is why this evaporation causes cooling sensation in our hands.

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

Ans: Tea in a saucer has larger surface area than in a cup. The rate of evaporation is faster with increased surface area. The cooling of tea in saucer takes place sooner than in a cup. Hence we are able to sip hot tea or milk faster from a saucer rather than a cup.

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

Ans: In summer we should wear light coloured cotton clothes as light colour reflects heat and cotton clothes have pores, which absorb sweat and allows the sweat to evaporate faster. Hence causing a cooling effect.

EXERCISES

Page No.12

1. Convert the following temperatures to the Celsius scale.

(a) 293 K
Ans: 293K = (293 – 273)°C = 20°C

(b) 470 K.
Ans: 470 K = (470 – 273)°C = 197°C

2. Convert the following temperatures to the Kelvin scale.

(a) 25°C
Ans: 25°C = (25 + 273)K = 298 K

(b) 373°C.

Ans: 373°C = (373 + 273)K = 646 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.
Ans:(a) At room temperature, naphthalene balls undergo sublimation and they directly changes into vapour state without leaving any solid. That is why Naphthalene balls disappear with time without leaving any solid.

(b) Perfume contains volatile solvent and diffuse faster and can reach people sitting several metres away. That is why we can get the smell of perfume sitting several metres away.

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

Oxygen < water <  sugar.

5. What is the physical state of water at —

(a) 25°C          (b) 0°C            (c) 100°C

Ans: (a) At 25°C, water is in liquid state.

(b) At 0°C, water is both in solid or liquid state.

(c) At 100°C, water is both liquid and gaseous state.

6. Give two reasons to justify

(a) water at room temperature is a liquid.

(b) an iron almirah is a solid at room temperature.

Ans: (a) At room temperature (25°C), water is a liquid because it has the following characteristics –

(i) At room temperature, water has no shape but has a fixed volume that is it occupies the shape of the container in which it is kept.

(ii) At room temperature, water follows.

(iii) At room temperature, water have weak intermolecular forces between their particles.

(b) At room temperature, an iron almirah is a solid because –

(i) It has a definite shape and volume like a solid at room temperature.

(ii) It is rigid as solid at room temperature.

(iii) It contains strong intermolecular forces between their particles.

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

Ans: Ice at 273 K will absorb heat energy or latent heat from the medium to overcome the fusion to become water. Hence the cooling effect of ice is more than the water at same temperature because water does not absorb this extra heat from the medium.

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

Ans: Steam at 100°C will produce more severe bums as extra heat is hidden in it called latent heat whereas the boiling water does not have this hidden heat.

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

Ans:

(A) Solid   →   Liquid   →   Melting/Liquefication/Fusion

(B) Liquid   →   Gas   →   Evaporation/Vapourisation

(C) Gas   →   Liquid   →   Condensation

(D) Liquid   →   Solid   → Solidification

(E) Solid   →    Gas   →   Sublimation

(F) Gas   →   Solid   →   Solidification

Additional Questions

1. What is matter ?

Ans: All the things that occupy space and have mass are called matter. Matter is made up of particles.

2. What is “Pancha Tatva”?

Ans: Ancient Indian philosophers believed that matter was made up of five basic elements such as air, earth, fire, sky and water. These five  basic elements are called “.Pancha Tatva”.

3. What is the S.I. unit of mass ?

Ans: Kilogram (kg).

4. What is the S.I. unit of volume ?

Ans: Cubic metre (m3).

5. What is diffusion ?

Ans: The intermixing of particles of two different types of matter on their own is called diffusion.

6. What are the different types of matter ?

Ans: The different types of matter are (i) Soild (ii) liquid and (iii) Gas

7. What is the full form of LPG ?

Ans: Liquefied Petroleum Gas.

8. What is the full form of CNG ?

Ans: Compressed Natural Gas.

9. What is fusion ?

Ans: The process of melting that is, change of solid state into liquid state is called fusion.

10. What is melting point ?

Ans: The temperature at which a solid melts to become a liquid at the atmospheric pressure is called its melting point.

11. What is the melting point of ice ?

Ans: 273 K or 0°C.

12. What is the S.I. unit of temperature ?

Ans: Kelvin (K).

13. What is the relation between celsius scale and kelvin scale of temperature ?

Ans: 0°C = 273 K.

14. What is latent heat ?

Ans: The amount of heat required to change the state of matter from one form to another form without changing the temperature is called latent heat.

15. What is the latent heat of fusion ?

Ans: The amount of heat energy required to change 1 kg of a solid into liquid at atmospheric pressure at its melting point is called the latent heat of fusion.

16. What is boiling point ?

Ans: The temperature at which a liquid starts boiling at the atmospheric pressure is called its boiling point.

17. What is boiling point of water ?

Ans: 100°C or 373 K.

18. What is evaporation ?

Ans: The process of change of a liquid to vapours at any temperature below its boiling point is called evaporation.

19. What is the latent heat of vaporisation ?

Ans:The amount of heat energy required to change 1 kg of a liquid into gaseous state at atmospheric pressure at its boiling point is called the latent heat of vaporisation.

20. What is sublimation ?

Ans: The process of changing directly from solid to gas without changing into liquid state or vice versa is called sublimation.

21. What is dry ice ?

Ans: Solid carbon dioxide (CO2) is called dry ice.

22. What is solidification ?

Ans: The process of changing from liquid to solid is called solidification.

23. What is condensation ?

Ans: The process of changing from gas to liquid is called condensation.

24. What is humidity ?

Ans: The amount of water vapour present in air is called humidity.

25. Name the four factors affecting evaporation.

Ans: The four factors affecting evaporation are

(i) Surface area – If the surface area of a liquid is increased, the rate of evaporation increases.

(ii) Temperature – With the increase of temperature, evaporation increases.

(iii) Humidity – With the decrease of humidity, the rate of evaporation increases.

(iv) Wind speed – With the increase in wind speed, the rate of evaporation increases.

26. What is the unit of pressure ?

Ans: Pascal (Pa).

27. Why do we see water droplets on the outer surface of a glass containing ice-cold water ?

Ans: The water vapour present in air, on coming in contact with the glass of water, loses energy and gets converted to liquid state, which we see as water droplets.

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