RBSE Class 9 Science Chapter 1Matter in our Surroundings Solutions

This post includes all intext and end exercise questions answer prepared by our experienced faculties. These solutions give you opportunity to secure good grades in exams.

These solutions are based on NCERT Class 9 Science book prescribed by Rajasthan Board of Secondary Education.       

 

 Chapter 1 Matter in our Surroundings

 

Intext Questions

Answers of Questions on Page No. 3

Q1. Which of the following are matter?

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

Ans. 

Matter- Anything around us which occupies space, has mass and can be felt with our sense organs is called a matter. Following are the matter-

Chair, Air, smell, almonds, cold drink, and smell of perfume

Q2. Give reason for the following observation-

The smell of hot sizzling food reaches you several meters away, but to get the smell form cold food you have to go close.

Ans.

 The smell of food reaches us due to ‘Diffusion’. The rate of diffusion increases due to high temperature because kinetic energy of particles increases with increase in temperature. That’s why the smell of hot sizzling food reaches us several meters away and faster. But on the other hand smell of cold food does not get diffused so fast that’s why we have to go close to get its smell.

Q3. A driver is able to cut through water in a swimming pool. Which property of matter does this observation show?

Ans.

The above activity explains the following properties of water (liquid state)

i.              The inner particle force of attraction is weak

ii.          Particles in liquid have larger space between them.

iii.       Particles of liquids move easily.

Q4. What are the characteristics of the particles of matter?

Ans.

i.     The particles have inter particle space between them.

ii.  The particles are moving continuously.

iii.The attraction force between the particles is weak.

iv.  The particles of matter are very small.

Answers of Questions on Page No. 6

Q.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

Ans.     

The density of a substance depends upon the no. of

particles per unit volume as well as upon their mass. On

the basis of these three factors, i.e., no. of particles, size

of particles and force of attraction the substances can be

arranged in increasing order of density as follow-

     

 Air < exhaust from chimneys < cotton < water < honey < chalk < iron

 

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

Ans.     

 

Properties	Solid	Liquid	Gas
Shape	Definite	Indefinite	Indefinite
Volume	Definite	Definite	Indefinite
Inter-particle attraction	Strong	Lesser than solids	Very weak
Compressibility	Negligible	Very small	High
Rigidity	Very hard	Less rigid	Compressibility
Fluidity	No fluidity	Fluidity	High fluidity
Diffusion	Negligible	Slow	Very fast
Kinetic energy	Very low	Higher than solid	Very high

(b)      comment upon the following :

Rigidity, compressibility, fluidity, filling a gas container,

shape, kinetic energy and density.

Ans.     

(i) Rigidity – It is the tendency to maintain the shape, when some outward force is applied. The rigidity is highest in solid matter.

(ii) Compressibility – It is the tendency to decrease the volume on application of force. The matter has inter molecular space between them, when external force is applied on them the particles come closer, this is known as compressibility. The compressibility is highest in gases because of largest inter-particle spaces. 

(iii) Fluidity –  The tendency to flow is called fluidity. The fluidity is highest in gases due to very weak inter-particle force of attraction. Liquids also have tendency to flow but their fluidity is smaller than gases due to comparatively smaller inter-particle distances.

(iv) Filling of a gas container – The gas particles vibrate and moves in all directions so they fill the container of  all shape and size. The gas particles occupy all space in the container.

(v) Kinetic energy- The energy possessed by the particles  due to their motion.In gases the inter-particle  spaces are large while inter-particle force of attraction is small. Due to this reason, the particles of gases move with high speed hence, have highest kinetic energy. Kinetic energy of liquids is lesser than gases, while it is least in solids at room temperature.

(vi) Density-It is the mass occupied by a matter per unit volume. It can be obtained by dividing the mass of a particular solid by the volume occupied by that mass of the solid. (mass/volume)

(vii) Shape-The shape of the matter depends on the inter-particle force of attraction and inter-particle spaces. The solids have fixed shape due to strongest force of attraction and smallest inter-particle spaces on the other hand liquids do not have fixed shape due to comparatively weaker force of attraction and larger inter-particle spaces.  

 

 

Q.3 Give reasons: (i) A gas completely fill the vessel in which it is kept?

Ans.

(i) The particles of gas move freely in all directions with

different speeds. A gas in the vessel completely fills it in

which it is kept due to the phenomenon of diffusion.In

gaseous state the inter-particle spaces are very large

hence, they readily fill the vessel completely due to their

motion.

(ii)  A gas exerts pressure on the walls of the container?

Ans.     

Force per unit area is called pressure. The particles of gas

moving with high speed strike the wall of the container

and exerts force on it.

(iii) A wooden table should be called a solid?

Ans.     

A wooden table should be called a solid because it has

definite shape, fixed volume, incompressible nature,

rigidity and no movement of the constituent particles

present in them.

(iv) We can easily move our hand in air but to do so the same through a solid block of wood we need a ‘karate expert’.

Ans.

The inter-particle spaces in air are very large while inter

particle force of attraction is very weak. This  is the

reason that our hand can move, in air. But the inter

particle spaces in solid are very small and inter-particle

force of attraction is very strong. So we cannot  easily

overcome  but  only a ‘karate expert’ with high-power 

can separate the particles of solid.

 

Q.4 Liquids generally have lower density as compared to solids but you must have observed that ice floats on water. Find out why?

Ans.     

Liquids have lower density as compared to solids. But the

solid form of water like ice floats on the surface of liquid

water. It indicates that the density of solid form of water

is lower than liquid form of water. This is due to open

cage like structure of ice. So there is some vacant spaces

are left in ice Therefore due to larger vacant spaces the

volume of ice increase hence, density decreases. That’s

why  it floats over the surface of  water.                                                                                                                                                                                             

Answers of Questions on Page No. 9

Q.1 Convert the following temperature to Celsius scale.

       (a) 300K            (b) 573K

Ans.

The relation between Kelvin scale and Celsius scale is as follows:

         t(℃)=t(K)-273

        (a).  t(℃)=300-273=27℃

       (b).   t(℃)=573-273=300℃            

    

Q.2 What is the physical state of water at?

       (a) 250⁰C           (b) 100⁰C

Ans.     

(a)  250  is higher than the boiling point (100  of water.

Therefore, the physical state of water at 250⁰C  is

gaseous state.

(b)  At 100⁰C, water starts boiling, so water exists both as a liquid as well as a gas.

 

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

Ans.     

When the change of state of substance beings, the energy

which is now supplied is being used up as latent heat or

hidden heat. Now the heat supplied is used up to

overcome the inter-particle force of attraction. As a result

the temperature remains constant during melting and

boiling of a substance.

 

Q.4 Suggest a method to liquefy atmospheric gases?

Ans.     

Atmospheric gases can be liquefied either by decreasing

temperature or by increasing pressure. During

liquefaction of atmospheric gas the constituent particles

have to be brought closer to each other and this is done

by cooling and applying pressure on it.

Answers of Questions on Page No. 10

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

Ans.     

During hot and dry the temperature of the atmosphere is

high and humidity of air is low. The rate of evaporation

increase as temperature increases and humidity

decreases. So , desert cooler cools better on a hot dry day.

 

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

Ans.     

The water is kept in an earthen pot (Matka) become cool

during summer due to the following reasons:

i).In summer, the temperature is high so the rate of

evaporation increases so, cooling increases.

ii). The particles of water with high kinetic energy escape

through the pores of earthen pot (matka) and evaporates,

since evaporation causes cooling thus, the water cools.

 

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

Ans.     

Acetone or petrol or perfumes are liquids with low

boiling points, when they are put on palm then they

absorb heat energy of palm and evaporate rapidly, so the

palm feels cold.

 

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

Ans.     

When surface area is increase then rate of evaporation

also increases so When hot tea or milk is poured in a

saucer which has larger surface area than the surface area

of a cup, the  rate of evaporation increases and tea or

milk becomes little cooler more quickly. Thus it becomes

easier to sip hot tea or milk from a saucer rather than a

cup.

 

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

Ans.       

We  should wear  light coloured cotton clothes because

during summer we perspire more and cotton have

tendency to absorb sweat and allows the sweat to

evaporate faster, this gives us cooling effect in summer.

 

Answers of End Exercise Questions     

Q.1 Convert the following temperatures to the Celsius scale:

       (a)  293 K                 (b)  470 K

Ans.      

(a)  293 K

 

 t(℃)=293-273=20℃

(b)      470 K

 t(℃)=470-273 = 197℃

               

Q.2 Convert the following temperature to the Kelvin scale.

       (a)  25⁰ C                 (b)  373⁰ C

Ans.     

    t(K)=t(℃)  + 273

    (a). 25℃

     t(K)=25 + 273=298K

      (b). 3730 C

       t(K)=373 + 273=646K

             

Q.3 Give reasons for the following observations:

(a)Naphthalene balls disappear with time without leaving

any solid.

      

(b)We can get the small of perfume sitting several meters

way.

Ans.    

(a)Naphthalene is a volatile solid which show

sublimation at room temperature. As a result it gets

converted into gaseous state. That’s why Naphthalene

balls disappear with time without leaving any solid.

(b)We can get the smell of perfumes sitting several meters away because perfumes have volatile substances and they diffuse faster in the air. During diffusion the particles of the perfume mix with the particles of air and reach us sitting several meters away.

 

Q.4 Arrange the following substances in increasing order

of forces of attraction between the particles- water, sugar,

oxygen.

Ans.      

We know that order of force of attraction between the

constituent particles is as follows:

Solid > liquid > gas

 Therefore, the force of attraction between particles in

increasing order is as follows:

Sugar > water > oxygen

 

Q.5 What is the physical state of water at?

       (a) 25⁰ C    (b)  0⁰ C      (c)  100⁰ C 

Ans.      

(a) At 25⁰ C, the physical state of water is a liquid.

(b)At 0⁰ C the physical state of water can be either a solid

(ice) or a liquid.

(c)  At 100⁰ C the physical state of water can be either a

liquid or a gas (steam).      

 

Q.6 Give two reasons temperature is liquid.

 (a)  Water at room temperature is liquid.

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

Ans.      

(a) Water is liquid at room temperature due to the following reasons:

(i)    Water takes the shape of the vessel in which it is kept. So water does not have fixed shape, so it is a liquid.

(ii)  The freezing point of water is 0  at which it becomes solid(ice) and boiling point is 100  at which it begins to convert into gas. The room temperature lies between 0  to 100 , that’s why it is liquid at room temperature.

(iii) Water can be poured from one vessel into another vessel. So water has fluidity i.e. it can flow as a liquid.

(b)An iron almirah is a solid at room temperature due to the following reasons:

(i) An iron almirah is hard and incompressible in nature that is, it has fixed shape, so it is a solid.

(ii)The melting point of iron is very higher than room temperature that’s why it is solid.(iii) An iron almirah cannot diffuse on itself through air i.e., it can not diffuse so it is solid.

 

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

Ans.  

Ice (solid state of water) has extra energy in the form of

latent heat of fusion as compared to water (liquid).so ice

absorbs more energy from surrounding whereas water

does not absorbs energy at the same temperature, Thus,

ice at 273K causes more cooling than water at the same

temperature.

 

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

Ans.      

Steam at 373K (100  absorbs energy equal to latent heat

of vaporization from surroundings and boiling water does

not have latent heat Thus, steam  at 373K (100⁰C) have

more energy than water at the same temperature and

hence, steam produce more severe burns than boiling

water.

 

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

 

 

 Ans.  

 A= Fusion (melting)

 B = Vaporization                      

 C = condensation (Liquefaction)

 D = Solidification (Freezing)

 E = Sublimation

 F = Sublimation (Solidification of gaseous state)