Physics

Sound

Mixing of Two Gases

Air is a colourless gas (or mixture of gases). When a gas jar is empty, it is actually filled with air. This because since air is colourless, we cannot see it in the gas jar. Bromine is a red-brown liquid. It forms vapour easily. Bromine vapour (or bromine gas) is red-brown in colour, and it is heavier than air. Let us perform the experiment now.
A gas jar containing air is placed upside down on a gas jar of bromine vapour [see Figure 5(a)]. We will see that the red-brown in colour vapours of bromine from the lower gas jar spread up into air in the upper gas jar. And after some time, the gas jar containing air also becomes completely red-brown in colour[see Figure 5(b)J.
The spreading up of bromine vapour into air can be explained as follows : Both air and bromine vapour are made of tiny moving particles. The moving particles of bromine vapour and air collide with each other and bounce about in all directions, due to which they get mixed uniformly. This is another example of diffusion. Please note that though bromine vapour is heavier than air, even then it goes up (against gravity) 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. Another point to be noted is that air present in the upper gas jar also diffuses downwards into bromine vapours in the lower gas jar but since air is colourless we cannot notice its presence in the lower gas jar.
The process of diffusion gives us two conclusions about the nature of matter :
(i) that matter is made up of tiny particles, and
(ii) that the particles of matter are constantly moving.
Before we go further, we should know the meaning of terms 'pollen' and 'pollen grain'. Pollen is a powdery substance discharged from the male part of a flower called stamen. Pollen is actually present in the top part of stamen called 'anther'. Pollen contains microscopic particles called pollen grains. Thus,pollen grains are extremely minute and light particles.

Notes

Sound - Notes

1. 3. Humidity of Air