Matter in Our Surroundings

Matter in Our Surroundings


Chapter – 1 (Chemistry)


Everything in this universe is made up of material which we named as “matter”.
Example – Stars, plants, clouds, stones are all matter.
So, we can define matter as materials which occupy space and have mass.


1.1 Physical nature of matter –

Matters are made up of millions of tiny particles. The particles of matter are very small.

1.2 Characteristic of particles of matter –

• Particles of matter have space between them.- When we make tea, it gets evenly distributed this means that particle of one type of matter gets into the space between the particles of the other.
• Particle of matter are continuously moving.- As the temperature rises, particles move faster. So we can say that with the increase in temperature, the kinetic energy of the particles also increases.
• Particles of matter attract each other- there is the force between particles of matter which we call ” attraction force “ which keeps the particles together the strength of this force of attraction varies from one kind of matter to another.


1.3 States of matter – 

There are three states of matter:
• The solid-state
• The liquid state
• The gases states

The solid-state- Here are the properties of solid-state

a) Definite shape.
b) Distinct boundaries.
c) Fixed volume.
d) Negligible compressibility as particles is so close to each other.
e) Least intermolecular distance.
f) Maximum intermolecular force.
Example -Brick, stones, wood etc.

The Liquid state- Here are the properties of liquid state:
a) Not fixed shape
b) Fixed volume did take up the shape of the container in which they are kept not rigid.
c) Liquid flows
d) Less compressibility as particles have some space between them.
e) More intermolecular space than solid.
f) Less intermolecular force than solid.
Example – Water, petrol etc.

Note- solids, liquids and gases can diffuse into liquids.
•The rate of diffusion of liquid is higher than that of the solid because in the liquid state particles move freely and have a bigger space between each other as compared to particles in the solid-state.
• The gases from the atmosphere dissolve in water especially Oxygen and Carbon dioxide so this is the reason that all the aquatic animals can breathe underwater as oxygen is dissolved in water.

The gaseous state – Move randomly at the high speed.
b) Not fixed shape.
c) Not fixed volume.
d) Highly compressible.
e) Least intermolecular force
f) Most intermolecular distance.
Example – Oxygen, carbon dioxide etc.

Note- The pressure exerted by the gas is because of this force exerted by gas-particle per unit area on the wall of the container.


1.4 Can matter change its state –

There the three States of matter solid, liquid and gas which are interchangeable.

• Effect of change of temperature: On increasing the temperature of solids it converts to the liquid which on further heating get converted into the gaseous state get converted into the gaseous state. We can explain it as follow.

As the temperature of solid increases, the kinetic energy of particles also increases. It gives enough energy to particles so that they start vibrating with a greater speed which helps overcome attraction force between the particles. Particle started moving freely at the particular stage and get free to move. At this stage, solid melts into a liquid with a very low force of attraction. Now if we apply heat on the liquid then the remaining force of attraction will break totally and particles are free to move. A stage reached the temperature at which a liquid start changing into gas.

• The minimum temperature at which solid melts to become a liquid at atmospheric pressure is called its melting point. The melting point of ice is 273.15 Kelvin.

• The temperature at which liquid stars bowling and atmospheric pressure. A boiling point for water the temperature is 373 kelvin.

•Effect of change of pressure:
Solidification- The transition of phase from liquid to solid by lowering the temperature below the freezing point.
 Fusion- change of solid into a liquid.
Vaporization- The process of transition of the liquid state into the gaseous state.
Condensation- The phenomenon of change of gas into a liquid.
Sublimation- The transition of solid directly into a gas.
Deposition- Conversion of the gaseous state directly into the solid-state.


1.5 Evaporation:

The phenomenon of change of a liquid into vapour at any temperature below its boiling point is called evaporation.
•Factors affecting evaporation –
a) As the surface area increases, the rate of evaporation also increases.
b) Evaporation increases as an increase in temperature.
c) With a decrease in Hindi dirty the rate of evaporation increases.
d) Increase in wind speed increases the rate of evaporation.


NCERT SOLUTIONS


Page – 3


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

The following substances are matter – Chair, air, almonds, lemon, water.

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:

The smell of hot sizzling food get diffused at a high rate in the atmosphere so it reaches us several metres away but the smell from cold food does not get diffused in the atmosphere.

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

The diver is able to easily cut through the water in the swimming pool because Water is in the liquid state having a very less intermolecular attraction between them and are easily breakable.

4-What are the characteristics of the particles of matter?
Answer:

Particles of matter have the following characteristics –
(a) Presence of intermolecular spaces between particles.
(b) Particles are in continuously moving.
(c) They attract each other and we call this intermolecular force of attraction.


Page – 6


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 the chimneys, honey, water, chalk, cotton and iron.
Answer:

The following substances are arranged in the increasing density:
Air< Exhaust from chimney< Cotton< Water< Honey< Chalk< iron.

2-Answer the following.
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.
Answer:

(a) The difference in the characteristics of the three states of matter.

Characteristics Solid Liquid Gas
Shape Fixed shape No Fixed shape No Fixed shape
Volume Fixed volume Fixed volume No Fixed volume
Intermolecular force Maximum Less than solids Very less
Intermolecular space Very less More than solids maximum
Rigidity/Fluidity Rigid/cannot flow Can flow/not rigid Can flow/not rigid
Compressibility negligible compressible Highly compressible

(b) (i) Rigidity: Property of a substance by which its shape remains fixed when treated with an external force.

(ii) Compressibility: External pressure applied to the object to contract its the intermolecular force which in turn reduce its density.

(iii) Fluidity: Property of liquid to flow.

(iv) Filling the gas container: Gas has that property by which it takes the shape of the container in all possible direction.

(v) Shape: Fixed structure of an object.

(vi) Kinetic energy: Energy possess due to the motion of an object.
It can be expressed as
K.E =1/2mv²
where,
‘m’ =mass
v’ = velocity
(vii) Density: It is the mass per unit volume of a substance. It is expressed as:
d = M/V,
where,
‘d’ = density,
M’ is the mass
‘V’ is the volume

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.

Answer:

(a) Gas has the least intermolecular force so molecules of a gas move in all possible directions.

(b) Due to high kinetic energy, molecules of gases hit the walls of the container as well as with other gas molecules which exerts pressure.

(c) This is because the table has a rigid shape and a definite volume.

(d) Because the intermolecular force is very less in the air so they are least dense and it is easy to break the bond whereas, it is hard to move hand through a solid block of wood because the molecules are closely packed so they are very dense and bonds are not easily breakable.

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

Ice is solid but the density of ice is less than the density of water. The molecules in ice make a cage-like structure with a lot of vacant spaces, this makes ice float on water.


Page: 9


1-Convert the following temperature to Celsius scale:
a. 300K b. 573K
Answer:

a) 300 k. –
As we know,0°C=273K
= (300-273)°k
= 27°C

b. 573K
= (573-273)°C
= 300°C

2-What is the physical state of water at:
a. 250°C b. 100°C?
Answer:

(a) At 250°C – As the boiling point of water is 100°C and here temperature extends from the boiling point of water so this must be a gaseous state.
(b) At 100°C – the water is at its boiling point. So it is a transition phase between liquid and gaseous state.

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

This is because Changes of state are neither exothermic nor endothermic that means there is no absorb or release of heat because the heat energy which is provided to change the state, is all used up to break the intermolecular force between molecules.

4-Suggest a method to liquefy atmospheric gases.
Answer:

Atmospheric gases are liquefied by increasing the pressure so that molecules of gases come closer and reached the state when they get liquefied.


Page: 10


1-Why does a desert cooler cool better on a hot dry day?
Answer:

As we know the rate is evaporation increases with increase in temperature and a decrease in humidity. In the desert , the temperature is high and the air is dry that means have less humidity, so the rate of evaporation increases which causes cooling effect.

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

The earthen pot contains many porous and when we put water in it then the heat inside it used up to convert water into vapours because of the process of evaporation. This causes the cooling effect and keeps water cool.

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

when we put acetone, petrol and perfume on our palm, it absorbs heat from our body and gets vaporized which causes cooling effect and we feel cold.

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

As we know that more the surface area, more the rate of evaporation. Here saucer has a larger surface area than a cup which means the rate of evaporation in more in saucer than a cup so tea cools down more quickly in the saucer.

5-What type of clothes should we wear in summer?
Answer:

It is preferred to wear light-coloured cotton clothes in summer because light colour clothes do not absorb heat and absorb sweat which on evaporation keeps our skin cool.


Exercise


1-Convert the following temperature to Celsius scale.
(a) 293K (b) 470K
Answer:

As we know that 0°C is equal to 273K that is
. 0°C =273 k
So,
(a) 293K
= (293 – 273)°C
= 20°C.

(b)470K
= (470 – 273)°C
= 197°C.

2-Convert the following temperatures to the Kelvin scale.
(a) 25°C (b) 373°C
Answer:

(a)25°C
= (25+273)K
= 298K.

(b) 373°C
= (373+273)K
= 646K.

3-Give reason for the following observations:
(a) Naphthalene balls disappear with time without leaving any solid.
Answer:

Naphthalene balls are in solid-state. At room temperature, balls started to convert directly into vapours due to the process of sublimation
(solid-state directly converts to the gaseous state.) and disappear with time without leaving any solid.

(b) We can get the smell of perfume while sitting several metres away.
Answer:

Perfumes are gaseous in nature so molecules of perfume are free to move as there is no intermolecular attraction between them. Molecules of air move at a higher speed and have large intermolecular spaces and these molecules of perfume get diffused in atmosphere fastly and we are able to smell the perfume the aroma while sitting several metres away.

4-Arrange the following in increasing order of forces of attraction between the particles – water, sugar, oxygen.
Answer:

Increasing order of forces of attraction between the particles –
Oxygen < water < sugar.

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

(a) 25°C – liquid form
(b) 0°C-freezing point of water
(c) 100°C-boilimg point of water

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

(a) This is because it has no fixed shape at room temperature and it takes the shape of a container. At room temperature, water boils at 100 °C and freezes at 0°C.

(b) An iron almirah is a solid as it has fixed volume and rigid shape at room temperature.

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

Ice is more effective in cooling than water at 273 K because of the extra heat (Latent heat )which ice absorb from the medium and water do not have this property of absorption of latent heat.

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

Steam produces more severe burns.

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

Answer:

A-Melting
B-Evaporation
C-Condensation
D-Solidification
E- Sublimation
F- Sublimation