Diffusion

Brownian Motion: The zig-zag or random path travelled by the particles of matter is called Brownian motion.

→ Intermixing of particles of two different types of matter on their own is called diffusion.

The rate of diffusion increases on increasing the temperature of the diffusing substance (by heating).

Example - The colour of ink spreading in water due to diffusion of particles of water.

 

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Chapter 1

Matter in our surroundings

Introduction

  • Everything in this universe is made of materials which scientist has names ‘matter’.
  • The matter is made up of very small tiny particles. It is not continuous but is particulate.
  • The matter is anything that occupies space and has mass.
  • Particles of matter have space between them and are continuously moving.
  • Particles of matter attract each other.

PHYSICAL NATURE OF MATTER

  1. Matter is made up of particles

If we take a 100 mL beaker, filling half of it with water and dissolve some salt/sugar. We will observe that there is no rise in water level and the salt/sugar has spread throughout the water (shown in the fig).

  1. How small are these particles of matter?
  • The particles of matter are very small – they are small beyond our imagination.

If we dissolve few crystals of potassium permanganate in about 1000mL of water, we will see the colour has changed. It shows that there must be millions of tiny particles in just one crystal of potassium permanganate, which keep on dividing themselves into smaller and smaller particles.

 

Chapter-1

Matter in Our Surroundings

Matter in Our Surroundings

Introduction

Let us know about the meaning of the title of this chapter “matter in our surroundings”. So to know about it we need to understand the term ‘surrounding’ first. Do you know what is meant by the word ‘surrounding’? Surrounding can be anything that is around us like air, clouds, buildings, water bodies, etc. These all are surroundings. Do you know that all the things that surround us are matter? Anything around us that has some mass and occupies certain space when we keep it, is called matter. In this chapter, we will be studying matter, its properties and much more.

Matter and its classification

Matter can be anything that occupies Space and has some Mass, (mass may be small or more doesn’t matter). Like we have LPG cylinder. Although it is filled with air only, but still it is too heavy. So, that is also matter as it has mass and occupies space. Even air is matter. If you see around, you will find that everything surrounding you is matter.

Classification of matter

Earlier when Matter was classified, then the ancient scientists said that matter was made up of five basic Elements called: Air, Fire, Earth, and Water & Sky. These five components are called as “panchtatva”.

But with the advancement in the field of science, it was concluded that matter can be classified on the basis of two main properties that is physical and chemical and therefore there are two main categories of matter, as follows –

Classification of Matter

  • Chemical Classification
  • Physical Classification

Physical and Chemical classification

Physical Classification

It is done on the basis of Physical Properties, i.e. the properties that we can see like rigidity, colour etc.

Chemical Classification

Is done on the basis of Chemical Composition of Matter that means what kind of particles are present, how they react with other, if they do not react then why so. Let’s do some activities to study about Matter. These activities are conducted in order to know more about matter and learn about their properties.

Activity: Do you know how we come to know that matter is made up of small particles? Let’s perform an activity: for this we need the following things

  • beaker, common salt, spoon glass rod

1. Fill beaker 3/4th with water mark the level of water on beaker, then add common salt to water.

2. On adding, we see that when we add salt to water it settles down.

3. On stirring, it starts disappearing and then a stage comes when it disappears completely.

Let s see what does this observation proves

  • As we are not able to see salt particles, this shows that it is not one continuous state of matter, instead it is formed of small particles.
  • Actually, on stirring, the salt particles get dissolved in water but still the level of water remains same. This shows that there are spaces between the particles of water which are occupied by the small salt particles.

Another activity: If we consider about the motion of particles. Do you actually think that they can show movement? If yes, lets track their movement?

In order to perform the activity, the following things are required – Stand, Agarbatti Match box

1. Now let’s take one stick out of packet, hold it on stand, place it in a corner of the room and light it. We will see that its fragrance gets spread evenly in the room.

2. The fragrance can be felt in whole room. It is not confined to one corner. So the observation is that “The whole room starts smelling very good“

The Conclusion to an activity

  • Is that particles of matter are not stationary. They are moving  continuously and when they drift through air, we can smell the pleasant fragrance.
  • The reason behind it is that when we light the stick, the heat energy supplied is taken by the particles, which increases their kinetic energy and this makes the fragrant particles to move rapidly. They easily drift through the air and spread fragrance.

You will be surprised to know the actual phenomenon involved behind this activity- The Phenomenon is called Diffusion.

Diffusion

It is the movement of any substance from a place of higher concentration to a place of lower concentration, or It can also be defined as the intermixing of different substances.

Activity to show diffusion: let’s take two flasks connected to each other by a knob.

Now let’s say on one side there is gas A and on the other side, there is gas B. When knob is closed, both the gases are in their own flasks. But when the knob is opened the two gases intermix rapidl y. As a result, both the flasks will have A and B gas particles. This intermixing is called diffusion. It is best shown by gases as the gas particles have maximum kinetic energy.

Activity to prove: particles of matter attract each other

Let’s take different substances like an iron nail, piece of wood, rubber band

1. Now try to break them by using hammer.

2. As we know, all three belong to same states – solids.

3. Can you guess what we noticed?

4. We noticed that it is easier to hammer down rubber band as compared to wood and iron nail.

5. The reason is that the particles in iron nail are so closely packed that it is difficult to separate those using hammer in comparison to wood or rubber band.

Conclusion of this activity:

In iron, the force of attraction between particles is maximum as particles are closer whereas in others they are not so close.

All these activities lead to the formulation of more information about matter and its properties which lead to the introduction of the Theory of Molecular Structure of Matter.