Matter in Our Surroundings Class 9 Notes Science Chapter 1

CHAPTER NOTES : MATTER IN OUR SURROUNDINGS

Introduction :-

Early Indian philosophers and ancient Greek philosophers classified matter in the form of five basic elements "Panch Tatva" _ air, earth, fire, sky and water. All living and non living things are made of these five basic elements.

In our surroundings, we see a large variety of things with different shapes, size and textures. Everything in this universe is made up of material which scientists have named "Matter", for example air, food, stones, clouds, stars, plants and animals, even a small drop of water or a sand particle are matter. The perception of joy, love, hate, thought, cold, hot, pain does not constitute matter while we perceive. 

Definition :- 

Material : The term used to describe a particular kind of matter, is called material e.g. : wood, water and marble. 

Type of material :

Matter : Anything which occupies space and has mass is called matter, so everything in the universe is "matter".

Some examples of matter are , water, air, metals, plants, animals etc. The matter can be classified into different categories depending upon its physical or chemical nature

(a) Matter is categorized as a gas, a liquid and a solid on the basis of physical state. For e.g. Air , water and the earth.

Changes of state are also matters of everyday experience for example, ice melts and water freezes, water changes into steam on heating and steam condenses to liquid water on cooling.

(b) On the basis of chemical nature matter is classified as an element compound or mixture. Elements and compounds are pure substances whereas a mixture contains two or more pure substances.

States of matter

Matter can be classified into 3 states on the basis of physical state-solids, liquids and gases.

Properties of solids :

(1) Solid state :

(a) A solid possesses a fixed volume and a definite shape, distinct boundaries and a definite mass.

(b) Solids are rigid and almost incompressible.

(c) Solids may break under force but it is difficult to change their shape.

(d) Solids generally possess high densities

(e) Solids do not exhibit diffusion.

(f) In solids intermolecular forces of attraction is more strong.

Example : Table, chair, common salt, silver, ice, diamond, stone, sugar etc.

Example of solid state :

(i) A wooden block should be called a solid.

Explanation : A wooden block has a fixed shape and is rigid. Hence, it should be called solid.

(ii) A rubber band undergoes a change in shape on stretching, still we call it a solid. 

Explanation : A rubber band is called a solid because although it undergoes a change in shape on stretching yet it regains the same shape when the force is removed.

Solids generally do not exhibit diffusion : Due to smaller interparticle spaces and absence of translatory motion.

Some example in solids which show diffusion:

(a) If we write something with chalk on a black-board and leave it as such for a few days, it becomes difficult to clean. This is due to diffusion of chalk particles into the surface of the black-board.

(b) If two metal blocks are bound tightly together and left undisturbed for a long time, it is observed that some particles of one metal diffuse into the surface of the other metal.

(2) Liquid state : Properties of Liquids :

(a) The matter in liquid state possesses a definite volume, a definite mass, but no definite shape.

(b) Liquids are also almost incompressible but are not rigid. In fact, they can flow from a higher to a lower level. Liquids have a property of fluidity and acquire the shape of the container in which they are kept.

(c) Liquids can undergo diffusion.

(d) Liquids also have high densities but less than that of solids.

(e) In liquids Intermolecular forces of attraction is weaker than solid.

Examples: Water, alcohol, milk, diesel, petrol, kerosene oil, vegetable oil, fruit juices etc.

Solids, liquids as well as gases can diffuse into liquids This is due to the fact that the interparticle spaces in liquids are larger and the particles in liquid state move freely.

(3) Gaseous state, Properties of Gases :

(a) The matter in gaseous state has neither definite volume nor definite shape but it has definite mass. It acquires the shape and volume of the container.

(b) Gases are highly compressible.

Physical nature of matter :

(1) Matter is made up of particles : The particle nature of matter can be demonstrated by a simple activity 

(a) Take about 50 ml water in 100 ml beaker.

(b) Mark the level of water.

(c) Add some sugar to the beaker and stir with the help of a glass rod.

(d) Observe the change in water level.

Conclusion : It is observed that the crystals of sugar disappear. The level of water remains unchanged. These observations can be explained by assuming that matter is made up of small particles. On dissolution, the particles of sugar get distributed into the spaces between particles of water.

(2) The constituent particles of matter are extremely small in size : The following activity demonstrates that the constituent particles of matter are very small.

(i) Take a 250 ml beaker and add 100 ml water to it.

(ii) Now add 2-3 crystals of potassium permanganate (KMnO₄) and stir with a glass rod in order to dissolve the crystals

(iii) Take 10 ml of this solution and add to 100 ml of water taken in another beaker.

(iv) Take 10 ml of this diluted solution and put into 100 ml of water taken in still another beaker.

(v) Repeat this process 10 times observe the colour of the solution in the last beaker.

Conclusion : (i) It is observed that the water in the last beaker is still coloured but the intensity of colour becomes light. It indicates that potassium permanganate (KMnO₄) crystal contains millions of tiny particles, some of which are still present even in the last beaker after so much dilution.

(ii) This experiment can be done by copper sulphate CuSO₄·5H₂O crystals, (for colours)

(iii) Dettol (for smell)

Characteristics of particles of matter :

(i) Particles of matter have space between them : Activity - When sugar is dissolved in water, the volume of the liquid remains unchanged. During dissolution, the particles of sugar get into the spaces between the particles of water. As a result, they get evenly distributed and there is no noticeable change in volume, similarly, when potassium permanganate is dissolved in water, its particle get evenly distributed throughout the bulk of water. This is indicated by uniform colour of the solution. This indicates that there are spaces between particles of matter. The particles of potassium permanganate get uniformly distributed in the spaces between water molecules.

Similarly when we prepare tea, coffee or lemonade (nimbu pani) we observe that particles of one type of matter get into the spaces between particles of other.

(ii) Particles of matter are continuously moving :

Activity 

(a) If an incense stick (Agarbatti) is lighted and placed in one corner of a room , its pleasant smell spreads in the whole room quickly. It demonstrates that the particles of matter possess motion. A burning incense stick produces some gases (vapour) having pleasant smell. The particles of these gases due to motion spread in the entire room and their presence can be felt by sensing the smell.

(b) Activity: To demonstrate that the kinetic Energy of particles increases with increase in temperature.

Kinetic energy : Kinetic energy is energy of motion and is usually defined as the work that will  be done by the body possessing the energy when it is brought to rest.

For a body of mass m having a speed v, the kinetic energy is =

(i) Take two beakers. To one beaker add 100 ml of cold water and to the other beaker add 100 ml of hot water.

(ii) Now add a crystal of potassium permanganate to both the beakers

Conclusion : It is observed that purple colour of potassium permanganate starts spreading and after sometime the entire solution becomes purple. The rate of mixing is faster in case of hot water. This experiment demonstrates that the particle of matter possess motion and that the kinetic energy of the particles increases with increase in temperature.

From these activities it is observed that when two different forms of matter are brought in contact, they intermix spontaneously. This intermixing is possible due to motion of the particles of matter and also due to the spaces between them. The intermixing takes place due to movement of particles of one form into the spaces between the particles of the other form of matter.

"This spontaneous intermixing of particles of two different types of matter is called diffusion "

The rate of diffusion becomes faster with increase in temperature because at higher temperature, the particles have more energy and hence move faster. 

(iii)  Particles of matter attract each other : There are some forces of attraction between the particles of matter which bind them together. The force of attraction between the particles of the same substance is known as cohesion. The force of attraction (or cohesion) is different in the particles of different kinds of matter.

The following activity may be carried out to demonstrate the attractive forces between particles of matter

(a) Take a piece of iron wire, a piece of chalk and a rubber band.

(b) Try to break them by hammering, cutting or stretching. It is observed that the piece of iron wire is most difficult to break. This indicates that particles in iron wire are held by stronger force of attraction as compared to particles in piece of chalk or rubber band.

Conclusion: Since energy is required to break crystals of matter into particles. It indicates that particles in matter are held by some attractive forces, the strength of these attractive forces varies from one matter to another.

Activity : 

To study diffusion of gases in water. 

Materials required : 200 cc beakers half filled with tap water, wire gauze, tripod stand, spirit lamp or bunsen burner.

Method : Place the wire gauze over tripod stand and then the beaker containing water. Heat the beaker by a spirit lamp or a bunsen burner on low flame. Do not allow the water to boil. Make your observations as the water is being heated and answer the following questions.
Activity : 1.7

To show the gases are far more compressible as compared to liquids.

Materials required : Two 50 ml syringes, two rubber corks, water.

Method : Take a syringe. Fill half of the syringe with water by drawing its plunger outward. Close the nozzle of the syringe with a rubber cork show in the figure (a). Now push the plunger inward with maximum force and record your observation. Stop applying the force and again record your observations.

Take another syringe. Fill half of the syringe with air by drawing its plunger outward. Close the nozzle of syringe with a rubber cork shown in the figure (b). Now push the plunger inward with maximum force and record your observations. Stop applying the force and again record your observation.

1.5.4 Differences between the liquids and gases : 

1. Liquids and gases are fluids. However, the liquids always flow in one direction, i.e., from a higher to a lower level, whereas the gases can flow in all directions.

2. Liquids are almost incompressible, whereas the gase are highly compressible.

3. A liquid has a well defined surface, such that it can be kept in an open container, from which it will not escape on its own.

On the contrary, a gas fills all the space in a container, in which it is kept. It does not have a free surface and is always kept in a closed vessel.

Study of compressibility of gases and liquids :

Activity

(i) Take three 100 ml syringes and close their nozzles by inserting them in a rubber cork. Remove the pistons from all the syringes.

(ii) Fill chalk pieces in the first, water in the second and leave third syringe as such. It already contains air.

(iii) Insert the pistons back into the syringes.

(iv) Compress all the syringes by pushing the pistons.

It is observed that when the syringe containing air, is compressed by applying pressure, the piston can move downward easily and it can be compressed to a larger extent. But when the second syringe containing water is compressed, it is compressed not easily and it can be compressed to much lesser extent than that of air. The first syringe containing chalk pieces (solid) is compressed with most difficulty.

Conclusion : This shows that gases are more compressible than liquids.

Explanation of solid, liquid and gas state on the basis of molecular structure 

In case of solids :

(i) The intermolecular spaces are very small and intermolecular forces are very large.

(ii) The molecules in a solid can vibrate about their mean positions, but cannot change their positions.

(iii) It is on account of this molecular arrangement, that solids have definite shape and definite volume.

(iv) They are incompressible.

In case of liquids : 

(i) The intermolecular spaces are some what large and intermolecular forces fairly small as compared to the solids.

(ii) The molecules of the liquid have large kinetic energy

(iii) It is on account of the larger kinetic energy and large intermolecular spaces that the molecules can interchange their position.

(iv) It is on account of this reason that liquids take the shape of containing vessel and flow from higher to lower level.

(v) The intermolecular forces in the liquids are sufficient to hold the molecules together and therefore, they have fixed volume.

(vi) They are incompressible.

In gas :-

(i) The intermolecular spaces are 1000 times or more than the liquids.

(ii) This in turn weakens the intermolecular forces to almost negligible magnitude.

(iii) The molecules of a gas are free to move about in any direction.

(iv) This accounts for the fact that gases have no definite shape or volume and occupy all the available space.

(v) Large intermolecular space.

(vi) They are easily compressible.

Example

(i) Cooking gas used in homes is liquefied petroleum gas (LPG) which is obtained by compressing petroleum gas into steel cylinders.

(ii) Compressed natural gas (CNG) is used as automobile fuel because the natural gas (methane) can be easily compressed.

(iii) The industrial gases such as ammonia (NH₃), chlorine (Cl₂), oxygen (O₂) etc. are compressed and transported to various places.
 

Comparision of characteristic properties of solids, liquids and gases :

Change of state of matter: A substance may exist in three states of matter i.e., solid, liquid or gas, depending upon the conditions of temperature and pressure. By changing the conditions of temperature and pressure, all three states could be obtained (solid, liquid, gas). On heating a solid changes into a liquid which on further heating changes into gas.

Example - Water exists in all the three states. 

Solid: Ice Liquid : Water. Gas : Water Vapour

Ice is a solid state and may be melted to form water (liquid) which on further heating changes into steam (gas). These changes can also be reversed on cooling.

Temperature and pressure are the two factors which decide whether a given substance would be in a solid, liquid or gaseous state.

(1) Effect of change of temperature : 

The effect of temperature on three states of matter could be seen by performing the following activity.

Activity :

(i) Take a piece of about 100 - 150g of ice in a beaker.

(ii) Hang a thermometer in it so that its bulb is in contact with ice.

(iii) Start heating the beaker slowly on a low flame.

(iv) Note down the temperature when ice starts changing of water & ice has been converted to water.

(v) Record all observations for the conversion of solid ice into liquid water.

(vi) Now, place a glass rod in the beaker and slowly heat the beaker with constant stirring with help of a glass rod.

(vii) Note the temperature when water starts changing into water vapours.

(viii) Record all observations for the conversion of water in the liquid state to vapour state.

It is observed that as temperature increases, the ice starts changing into water. This change is called "Melting". The temperature remains same till all the ice changes into water. The thermometer shows 0°C until all the ice has melted. On further heating, the temperature starts rising. At 373 K (or 100°C), water starts boiling. As the water continue boiling the temperature remains almost constant.

Conversion of ice to water and water to water vapour 

Explaination about interconversion of different three state of matter:

(i) Solid to liquid change (melting): Ice is a solid. In solids, the particles are tightly packed together. When we heat a solid, its particles become more energetic and kinetic energy of the particles increases. Dut to the increase in kinetic energy, the particles start vibrating more strongly with greater speed. The energy supplied by heat overcomes the intermolecular forces of attraciton between the particles. As a result, the particles leave their mean position and break away from each other. After this solid melts and a liquid is formed.

"The temperature at which a solid melts to become a liquid at the atmospheric pressure is called its melting point". The process of melting is also called "Fusion". The melting point of ice is 0°C. It may also be written as 273.16 K or 273 K.  

The temperature is represented in Celsius scale as °C. Now a days it is expressed on Kelvin scale (K). 

Conversion of temperature on Celsius scale to Kelvin scale: 

For example :_ 0°C = 0 273 = 273 K 

100°C = 100 273 = 373 K 

Conversion of temperature on Kelvin scale to celsius scale: 

For example :_ 373 K = 373 _ 273 = 100°C  

273 K = (273 273) = 0°C 

Latent Heat (Hidden Heat) :- 

It is observed that the temperature of the system does not change after melting point is achieved till all the ice melts, though we continue to heat the beaker. This is happen because the heat supplied is used up in changing the state by breaking the intermolecular forces of attraction which hold them in solid state. As a result, there is no change in temperature till all the ice melts. This energy required to change solid into liquid is called "latent heat". The word "latent" means "hidden" because this energy is hidden into the contents of the beaker.

Latent heat is of two types:

(a) Latent heat of fusion

(b) Latent heat of vaporization.

(a) Latent heat of fusion :

Latent heat of fusionis defined as the amount of heat energy required to change 1 kg of a solid into a liquid at atmospheric pressure without any change in temperature at its melting point". The latent heat of fusion of ice is 3.34 × 10⁵ J/Kg 

Note : The numerical value of melting point and freezing point is the same. For example, if melting point of ice is 0°C (273 K), then the freezing point of water is 0°C (273 K).

(ii) Liquid to gas change (Boiling or vaporizations) :

In a liquid most of the particles are close together. When we supply heat energy to the liquid, the particles of water start vibrating even faster. Some of the particles become so energetic that they can overcome the attractive forces of the particles around them. Therefore, they become free to move and escape from the liquid. Thus the liquid evaporates i.e., starts changing into gas.

"The temperature at which a liquid changes into a gas or vapour at the atmospheric pressure is called its boiling point". 

"Boiling" is a bulk phenomenon.

Example - For water, the boiling point is 100°C or 373 K. The particles in steam i.e., water vapour at 373 K have more energy than water at the same temperature. 

Reason : This is because the particle in steam have absorbed extra energy in the form of latent heat of vaporization.

(b) Latent heat of vaporization : The latent heat of vaporization of a liquid is the quantity of heat in joules required to convert 1 kilogram of the liquid (at its boiling point) to vapour or gas, without any change in temperature. The latent heat of vaporization of water is 22.5 × 10⁵ joules per kilogram (or 22.5 × 10⁵ J/kg).

The boiling point of a liquid also indicates the strength of intermolecular force of attraction between particles. Volatile liquids such as alcohol, petrol and acetone have very weak intermolecular forces. Therefore, they boil at low temperature. On the other hand, water has stronger intermolecular forces of attraction and therefore, it boils at higher temperature. When steam is cooled, it condenses to water & when water is cooled, it changes to ice.

Note : The numerical value of boiling point and liquefaction point is same.

For example , if boiling point of water is 100°C (373 K), then the liquefaction point of steam is 100°C (373K).

Condensing is opposite to evaporating and freezing is opposite to melting. 

Sublimation 

The process due to which a solid directly changes into gaseous state on heating, without changing first into liquid state and the gaseous state, directly changes into solid state on cooling, is known as "Sublimation"

Example : Ammonium chloride, camphor, iodine, naphthalene, solid carbon dioxide or (dry Ice), anthracene.

Sublime : A gaseous form, directly formed from a solid on heating, is known as sublime. 

Sublimate : A solid state of matter formed directly from its gaseous state on cooling, is called sublimate.

To understand sublimation process we can do an activity:

1. Take some camphor or ammonium chloride.

2. Powder it and put in a china dish.

3. Place an inverted funnel over the china dish.

4. Heat the china dish slowly.

We observe that solid camphor on heating gets converted into vapour which gets condensed on the funnel.

Solid state is directly converted into gaseous state. This experiment shows sublimation process.

(2) Effect of change of pressure:

Gases are compressible because on applying pressure, the space between the gaseous particles decreases. Therefore gases can be compressed readily.

By applying pressure and reducing temperature, the gases can be converted into liquids i.e. gases will be liquefied.

"This process of conversion of a gas into a liquid by increasing pressure or decreasing temperature is called liquefaction."

Thus, we can conclude that temperature and pressure determine the state of a substance; solid, liquid or gaseous.

Solid carbondioxide is also called dry ice. Solid CO₂ gets converted into gaseous state directly on decreasing pressure to 1 atmosphere without coming into liquid state.  

Interchange between different states 

Three conditions of temperature and pressure which decide the state of matter :_

• If the melting point of a substance is above the room temperature at the atmospheric pressure, it is called solid.
• If the boiling point of a substance is above room temperature under atmospheric pressure, it is classified as liquid.
• If the boiling point of the substance is below the room temperature at the atmospheric pressure, it is called gas.

Evaporation

"The process of a liquid changing into vapour (or gas) even below its boiling point is called evaporation".

Evaporation of a liquid can take place even at room temperature, though it is faster at higher temperatures. It is surface phenomenon because it occurs at the surface of a liquid only.

Whatever be the temperature at which evaporation takes place, the latent heat of vaporizations must be supplied whenever a liquid changes into vapour (or gas).

Explanation about Evaporation: Some particles in a liquid always have more kinetic energy than the others. So, even when a liquid is well below its boiling point, some of its particles have enough energy to break the forces of attraction between the particles and escape from the surface of the liquid in the form of vapour (or gas). Thus, the fast moving particles (or molecules) of a liquid are constantly escaping from the liquid to form vapour (or gas).

Examples :(i) Water in ponds changes from liquid to vapour without reaching the boiling point.

(ii) Water when left uncovered slowly changes into vapour.

(iii) When we put wet clothes for drying, the water from the clothes goes to the atmosphere.

Differences between evaporation and boiling:

Factors Affecting Evaporation

There are five factors which affects the rate of evaporation:

(i) Nature of liquid : Different liquids have different rates of evaporation. A liquid having weaker interparticle attractive forces evaporates at faster rate because less energy is required to overcome the attractive forces.

Example: Acetone evaporates faster than water.

(ii) Surface area of the liquid : The evaporation depends upon the surface area. If the surface area is increased, the rate of evaporation increases because the high energy particles from liquid can go into gas phase only through surface.

Example : (a) The rate of evaporation increases when we put kerosene or petrol in an open china dish than in a test tube.

(b) Clothes dry faster when they are well spread because the surface area for evaporation increases.

(iii) Temperature: Rate of evaporation increases with increase in temperature. This is because with the increase in temperature more number of particles get enough kinetic energy to go into the vapour state (or gaseous state) Example _ Clothes dry faster in summers than in winters.

(iv) Humidity in the air: The air around us contains water vapour or moisture. The amount of water present in the air is referred to as humidity. The air cannot hold more than a definite amount of water vapour at a given temperature. If the humidity is more, the rate of vaporization decreases. The rate of evaporation is more if the air is dry.

Example: Clothes do not dry easily during rainy season because the rate of evaporation is less due to high moisture content (humidity) in the air.

(v) Wind speed : The rate of evaporation also increases with increase in speed of the wind. This is because with increase in speed of wind, the particles of water vapour move away with wind resulting decrease in the amount of vapour in the atmosphere.

Example: (i) Clothes dry faster on a windy day.

(ii) In a desert cooler an exhaust fan sucks the moist air from the cooler chamber which results in greater rate of evaporation of water and hence greater cooling.

Evaporation causes cooling:

During evaporation, cooling is always caused. This is because evaporation is a phenomenon in which only the high energy particles leave the liquid surface. As a result, the particles having low energy are left behind. Therefore, the average molecular energy of the remaining particles left in the liquid state is lowered. As a result, there is decrease in temperature on the part of the liquid that is left. Thus evaporation causes cooling.

Example: (i) When we pour some acetone on our palm, we feel cold. This is because the particles gain energy from our palm or surroundings and leave the palm feeling cool.

(ii) We sprinkle water on the root or open ground after a sunny hot day. This cools the roof or open ground. This is because the large latent heat of vaporization of water helps to cool the hot surface.

Some other examples of evaporation:

(i) We should wear cotton clothes in hot summer days to keep cool and comfortable.

This can be explained as follows. We get a lot of sweat on our body in hot summer days. Cotton is a good absorber of water, so it absorbs the sweat from our body and exposes it to the air for evaporation. The evaporation of this sweat cools our body. The synthetic clothes (made of polyester etc) do not absorb much of sweat, so they fail to keep our body cool in summer.

(ii) We see water droplets on the outer surface of a glass containing ice-cold water.

Take some ice-cold water in a glass. Soon we will see water droplets on the outer surface of the glass. The water vapour present in air, on coming in contact with the cold glass of water loses energy and gets converted to liquid state, which we see as water droplets.

(iii) Water keeps cool in the earthen pot (matki) during summer:

When the water oozes out of the pores of an earthen pot, during hot summer, it evaporates rapidly. As the cooling is caused by evaporation, therefore, the temperature of water within the pot falls and hence it becomes cool.

(iv) Rapid cooling of hot tea:

If tea is too hot to sip, we pour it in the saucer. In doing so, we increase the surface area and the rate of evaporation. This, in turn, causes cooling and the tea attains a desired temperature for sipping

(v) A wet handkerchief is placed on the fore head of a person suffering from high fever. The logic behind placing wet cloth is that as the water from the wet cloth evaporates, it takes heat from the skull and the brain within it. This, in turn, lowers the temperature of brain and protects it from any damage due to high temperature.(vi) We often sprinkle water on the road in summer. The water evaporates rapidly from the hot surface of the road, there by taking heat away from it. Thus, the road becomes cool.

Plasma

(i) Plasma is a mixture of free electrons and ions.

(ii) Plasma is considered the fourth state of matter.

(iii) Plasma occurs naturally in the stars (including the sun). Inside the stars, the temperature is so high that the atoms break up. Some of the electrons break away from the atoms converting the rest of atoms into electrically charged particles called ions. This mixture of free electrons and ions in a star is called plasma.

(iv) The sun and other stars glow because of the presence of plasma in them.

(v) Plasma can also be made on the earth by passing "electricity through gases at very low pressure taken in a glass tube (called discharge tube).

(vi) Plasma makes a fluorescent tube (or neon sign bulb) to glow.

Bose-Einstein condensate (BEC) 

In 1920, an Indian scientist "Satyendra Nath Bose" did some calculations for the fifth state of matter. On the basis of these calculations, Albert Einstein predicted the existence of a new state of matter called Bose-Einstein condensate (BEC). The fifth state of matter called Bose-Einstein condensate was finally achieved by three scientists, Cornell, Ketterle and Wieman of USA by cooling a gas of extremely low density (about one hundred thousandth the density of normal air) to super low temperatures.