Matter in Our Surroundings (NCERT Solutions, Class 9)

Page 3

(1) Which of the following are matters?

Chair, air, love, smell, hate, almonds, thought, cold, lemon water, smell of perfume.

Ans-

Matters among the given examples are listed below –

Chair (Solid)

Air (Gaseous)

Almonds (Solid)

Lemon water (Liquid)

(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-

The increase in temperature increases the kinetic energy of the particles which increases their movement. Therefore, the smell of hot sizzling food reaches us several meters away.

The decrease in temperature decreases movement of the particles. Therefore, the smell of the cold food does not reach us several meters away. We have to go to close to the cold food.

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

Ans- A diver is able to cut through water in a swimming pool. It shows that particles of water have force of attraction and space between them. The force applied by the diver on the particles of the water is greater than force of attraction between them. The space between the particles also allow diver to cut the water in a swimming pool easily.

(4) What are the characteristics of the particles of matter?

Ans-

Characteristics of particles of matter

(i) Particles of matter have space between them. It means particles of one matter get into the spaces of particles of other matter.

Eg:- Coffee, tea, lemonade, potassium permanganate in water etc.

(ii) Particles of matter move continuously because of kinetic energy they possess.

Eg:- Fragrance of perfume spread in room by the movement of the gaseous particles. The particles of perfume settle between the space of the particles of the air.

(iii) The force between the particles keeps them together. Therefore, particles of the matter attract each other. The strength of this force of attraction varies from one kind of matter to another.

Eg:- We have to apply greater force on cutting of iron, breaking of chalk because of great force of attraction between particles of solid matter.

Page 6

(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 list of matter in order of the increasing density is given below –

Matter	State of the matter	Reason
Air	Gaseous state	Mass per unit of volume is lesser than exhaust from chimney because exhaust from chimney has carbon particles in it. These particles increases mass of the exhaust from the chimney. Therefore, density of exhaust from chimney is greater than the air.
Exhaust from chimneys	Gaseous state
Cotton	Solid	Cotton has many holes which are filled with air which increases mass of the cotton. Therefore, density of cotton is greater than given other articles.
Honey	Liquid	Honey has greater density than water.
Water	Liquid	Honey has greater density than water.
Chalk	Solid	Iron has greater density than chalk because its mass is greater than chalk.
Iron	Solid

(2) (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.

Ans-

(a) The differences in the characteristics of states of matter is tabulated below-

SN	Characteristics of the matter	Solid State	Liquid State	Gaseous State
1.	Space between particles	Very little space	Large space in comparison of solid particles	The largest space between particles of the gaseous state
2.	Shape	Definite	Take shape of container	Take shape of container
3.	Compressibility	No	Can compress	Has the highest compressibility
4.	Force of attraction	Highest	Higher than gaseous particles	Lowest
5.	Movement	Can not move freely	Can move	Move freely

(b)Rigidity – The property in which matter do not change their shape is called rigidity. Solids are the most rigid, liquids are less rigid than solid and gaseous particles are not rigid.

Compressibility – Compressibility is a property of matter in which volume of matter is reduced when we apply force on matter. Solid has no compressibility, liquid has more compressibility than the solids but gaseous matter has the highest compressibility.

Fluidity – Fluidity is the property in which matter can flow and can change their shape. Solids are not fluid but liquids and gaseous matter are fluids.

Filing a gas container – Filling a gas container means to take shape of the container.

Shape – Shape is the definite boundaries of the matter. Solids have definite boundary or shape. Liquids and gas do not have definite boundaries but they take shape of the container in which they kept.

Kinetic Energy – Kinetic energy is the energy which particles of matter have because of their movement.

Density – Density of any matter is mass per unit volume. Solid has highest density. Liquids have less density than the solids. Gaseous matter has the lowest 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) We can easily move our hand in air but to do the same through a solid block of wood we need a karate expert.

Ans-

(a) A gas has no definite shape and particles of gas can move freely. Therefore, a gas fills the vessel completely in which it is kept.

(b) A gas continuous move freely in the container. In this process of movement, particles of gas collide with walls of the container. Therefore, a gas exerts pressure on the walls of the container.

(c) Particles of the gas are very far to each other and force of attraction is very low between particles of gas but particles of solid are very close to each other and force of attraction is the highest. Therefore, we can easily move our hand in between the particles of air and to do the same through a solid block of wood we need a karate expert.

(4) Liquids generally have lower density as compared to solids. But you must have observed that ice floats on water. Find out why.

Ans- Ice floats on the water because it has less density than water. A solid can float on liquid if it is lesser dense than liquid and displace amount of liquid equal to its weight.

Page 9

(1) Convert the following temperature to Celsius scale:

(a) 300 K (b) 573K

Ans-

(a)T K = T ⁰C + 273K

300 K = T ⁰C + 273K

T ⁰C = 300K – 273K

= 27⁰C

Hence, 300K is equal to 27⁰C.

(b) T K = T ⁰C + 273K

573 K = T ⁰C + 273K

T ⁰C = 573K – 273K

= 300K

Hence, 573K is equal to 300⁰C.

(2) What is the physical state of water at:

(a) 250⁰C (b) 100⁰C

Ans-

(a) Water starts boiling at 100⁰C. Therefore, water will change in to gas state (steam) at 250⁰C.

(b) Water will start boiling at 100⁰C. Therefore, water will be in liquid state and gaseous state.

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

Ans- The temperature of the system does not change till all matter change its state. Even though, we continue to heat the matter. The heat energy (Latent heat) is used by the one matter without showing any rise in the temperature.

(4) Suggest a method to liquefy atmospheric gas.

Ans – Liquefaction is a process in which a gas can be liquefied by applying high pressure and low temperature.

Eg:- Petroleum gas is liquefied to LPG (liquefied petroleum gas) by using high pressure and low temperature.

Page 10

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

Ans- The water of desert cooler absorbs heat from our surroundings to evaporate and air becomes cool. On a hot dry day, water evaporates in large quantity. Therefore, we feel better on a hot dry day.

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

Ans-There are many pores on the earthen pot. The water evaporates through pores and water inside the pot becomes cool.

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

Ans-

When we put some acetone or petrol or perfume on our palm the particles of liquid gain energy from palm. Hence, we feel cool due to loss of energy.

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

Ans-The surface area of the saucer is greater than the surface area of the cup. When we pour hot tea on the saucer, it comes in contact of the large area and takes energy from the large area of the saucer. Hence, tea becomes less hot. Therefore, we can sip tea comfortably in saucer rather than in cup.

(5) What type of clothes should we wear in summer?

Ans- We wear cotton cloths in summer because cotton is a good absorber of the water. When we perspire, cotton absorbs it. The water absorbs heat from our body to evaporate and we feel cool.

Exercise

(1) Convert the following temperature to the Celsius scale.

(a) 293 K (b) 470K

Ans-

(a) T K= T ⁰C + 273K

293 K = T ⁰C + 273K

T ⁰C = 293K– 273K

= 20⁰C

Hence, 293K is equal to 20⁰C.

(b) T K = T ⁰C + 273K

470 K = T ⁰C + 273K

T ⁰C = 470K – 273K

= 197⁰C

Hence, 470K is equal to 197⁰C.

(2) Convert the following temperatures in the Kelvin scale.

(a) 25⁰C (b) 373⁰C

Ans-

(a) T K = T ⁰C + 273K

TK = 25 + 273

T K = 298K

Hence, 25⁰C is equal to 298K.

(b) T K = T ⁰C + 273K

TK = 373 + 273

T K = 646K

Hence, 373⁰C is equal to 646K.

(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) Naphthalene balls disappear with time without leaving any solid because of sublimation process. In this process solid matter can change in to gaseous matter directly without changing in liquid matter.

(b) We can get the smell of perfume sitting several metres away because particles of gaseous matter continuous move and particles of perfume get into the space between the particles of air.

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

Ans- The given substances are listed in increasing order of forces of attraction between the particles below –

Oxygen (Gas)

Water (Liquid)

Sugar (Solid)

(5) What is the physical state of water at –

(a) 25⁰C (b) 0⁰C (c) 100⁰C?

Ans-

(a) The physical state of water is liquid at 25⁰C.

(b) The physical state of water is solid at 0⁰C. If we give heat equal to latent heat of fusion then it will also find in liquid state.

(c) The physical state of water is gaseous (steam) and liquid at 100⁰C. The water starts boiling at 100⁰C. Therefore, it find in 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) Water at room temperature is liquid because particles of water can move freely and have less force of attraction. Therefore, water is found liquid at room temperature. At 0⁰C water changes in to ice and at 100⁰C water changes in to gas (Vapour).

(b) An iron almirah is a solid at room temperature because particles of iron have very strong force of attraction. Therefore, particles can not move and remain solid.

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

Ans- The ice at 273 K is more effective in cooling than water at the same temperature because ice at 273 K has less energy. But, water at same temperature possesses latent heat of the fusion. Therefore, ice at 273K is more effective in cooling.

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

Ans-

The steam produces more severe burn on the skin because steam has temperature more than boiling water temperature. When steam gets in touch with the skin it takes energy from skin to cools down. Because of very high temperature, skin gets burn. The steam passes heat to the skin by the process of condensation.

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

Matter in our surroundings, Q 9, diagram, NCERT,class 9