Characteristics and Properties of Matter - Matter in our Surrounding, Class 9, Science PDF Download

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 the 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 a 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 the 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 some time the entire solution becomes purple. The rate of mixing is faster in case of hot water. This experiment demonstrates that the particles 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 into contact, they intermix spontaneously. This intermixing is possible due to the 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 an increase in temperature because, at a 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 the iron wire are held by the stronger force of attraction as compared to particles in a piece of chalk or rubber band.

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

Activity: 

To study the 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 and 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 the syringe with a rubber cork shown in 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 gases 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 the 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 downwards 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 a definite shape and definite volume.

(iv) They are incompressible.

In case of liquids: 

(i) The intermolecular spaces are somewhat 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.
 

Comparison of characteristic properties of solids, liquids and gases: