Matter is made up of small particles

1. Dissolving a Solid in a Liquid:

• When Potassium permanganate a purple coloured solid substance is dissolved in water the colour of solution becomes purple because purple coloured particles of potassium permanganate spread throughout water making the whole water look purple.

Potassium permanganate

• On dissolving, the particles of potassium permanganate get into the spaces between the particles of the water.
• This shows that matter is composed of tiny particles and that there is apace between these particles.
• The particles of potassium permanganate and particles of water spread into each other and mix up on their own, so it is concluded that ‘they are moving’.
• If the particles were not moving, the colour could not spread throughout the beaker on its own.

2. Mixing of Two Gases:

• An empty glass jar is actually filled with air which is colour less when it is placed upside down on a jar containing bromine vapours the empty jar also becomes red-brown in colour.
• Elemental bromine exists as a diatomic molecule, Br₂. It is a dense, mobile, slightly transparent reddish-brown liquid, that evaporates easily at standard temperature and pressure to give an orange  vapor

Bromine

• Both air and bromine vapour is made of tiny moving particles. The moving particles of bromine vapour and air collide with each other and bounce about in all directions.
• Though bromine vapour is heavier than air, it goes up and mixes with air in the upper jar because its particles are moving with high speeds due to which they have sufficient kinetic energy to overcome the force of gravity and go up into the gas jar containing air.