Chapter 1.2
Characteristics of particles of matter

1. How can you prove that there is space between the particles of matter?

Add 100 ml of water to a beaker and mark the water level. Now add some sugar or salt to this water. This added matter will disappear in a few seconds or minutes and yet the level of water does not increase. This is because particles of the added matter like salt or sugar can get into the space between the particles of water in which they dissolved. This clearly proves that there is space between particles of matter.

2. What do you mean by diffusion? Explain with an example.

Matter is made up of tiny particles that are constantly moving. These particles move to distribute themselves evenly in the available space. They also interact with one another as they move. This intermingling of particles of matter because of their random motion is called diffusion. Diffusion of gas particles is faster than the diffusion of liquid particles.

Here is an example to prove this.

Put a lighted incense stick in one corner of the room. The smell of the incense will spread throughout the room within seconds. This is because the particles of scent in the incense stick intermingle with particles of air and spread out in all directions. This is how the scent of incense spreads throughout the room. This is also an example of the diffusion of incense particles into particles of air.

3. With the help of an activity prove that the particles of matter are constantly moving.

Drop a crystal of potassium permanganate in a glass tumbler containing water. Within seconds the colour of water will change and become that of potassium permanganate. This is because the particles of potassium permanganate are constantly moving through the spaces available between the particles of water.

4. What will happen when crystals of potassium permanganate are dropped into two beakers A and B containing hot water and cold water?

The crystals will settle at the bottom of the beakers and start diffusing. As time passes by, the particles of potassium permanganate will diffuse throughout the water. This clearly shows that particles of solids and liquids mix into one another. Diffusion occurs faster in the hot water because as temperature increases the kinetic energy of particles also increase. Consequently, they diffuse at an accelerated rate.

5. The rate of diffusion is faster in gases. Why?

The rate of diffusion is faster in gases because the intermolecular attraction is considerably low in gases.

6. When a bottle of perfume is opened, its scent spreads throughout the room. Explain the property involved.

Diffusion is the property involved. Since the intermolecular attraction between the particles of air is minimum, they are free to move in a chaotic manner at high speed throughout the vessel that contains them. When a bottle of perfume is opened, the particles of the perfume will move in all directions at random speed and mix with other gas particles in the air and thus they reach our nose instantaneously.

7. Name the property of gases that helps us in detecting the leakage of LPG gas

Diffusion

8. Give examples of the following:
a) Liquid diffusing into solid
b) Solid diffusing into liquid
c) Solid diffusing into solid

Answer (a) Liquid diffusing into solid

If we spill a few drops of ink on a clean bloating paper, the ink will spread out. This is an example of diffusion of a liquid into a solid.

Answer (b) Solid diffusing into liquid

If we drop a crystal of potassium permanganate into a beaker containing water, the colour of potassium permanganate will spread throughout the water. This is an example of a solid diffusing into liquid.

Answer (c) Solid diffusing into solid

It takes a lot of time for a solid to diffuse into another solid. Because of this reason it is rare for solids to diffuse into another solid. Here is an example. With a piece of chalk write something on a blackboard. When the writing is fresh, it can be cleaned easily. But if we leave the writing uncleaned for a few days, it becomes difficult to clean the blackboard. This is because chalk particles have diffused into the blackboard.

9. You cannot cut a stream of water. Why?

We cannot cut a stream of water because of the force of attraction existing between the particles of water.

10. List 3 characteristics of particles of water. Describe one example of each characteristic. Name the characteristics which are responsible for (a) spreading of smell of scent in a room and (b) water taking shape of the vessel in which it is poured.

Characteristics of matter

i) There is space between the particles of matter

Add a small amount of sugar to water. It will dissolve in the water without increasing the level of the water. This is because sugar particles occupied the space between the particles of water.

ii) Particles of matter move constantly

Add a crystal of copper sulphate into a beaker containing water. Within seconds the blue colour of copper sulphate will spread throughout the water in the beaker.

iii) Particles of matter attract each other

Put your finger across water running from a tap. This will break the stream but when you remove the finger the stream will continue its course.

a) Diffusion is the property that spreads the smell of scent throughout the room.
b) Water assumes the shape of the container because of its non-rigidity.

10. Does density affect the rate of diffusion?

Yes, density affects the rate of diffusion. Dense liquids diffuse at a slower pace. For example, honey is denser than ink. Fill two jars with water. Add a drop of honey into the first jar and a drop of ink into the second jar. It can be observed that honey takes longer than ink to reach the bottom of the jar. This is because density affects the rate of diffusion of liquids.

11. Does temperature affect the rate of diffusion?

Yes, temperature affects the rate of diffusion. The rate of diffusion increases when there is an increase in the temperature. For example, liquids diffuse faster at higher temperatures.

12. Sound and light are not considered as matter. Why?

Sound and light are not considered as matter because they do not have mass. They do not occupy space either.