Atoms 1.4 describe and explain experiments to investigate the small size of particles and their movement including: i dilution of coloured solutions ii diffusion experiments

Dilution of coloured solutions

When potassium manganate (VII) crystals are dissolved in water, a purple solution is formed. A very few tiny crystals can produce a highly intense colour. 
When this solution is diluted several times, the colour fades, but does not disappear until a lot of dilutions are made.
This indicated that there are a large number of particles of potassium manganate (VII) in a very small amount of solid. If this is true, then the particles of potassium manganate (VII) must be very tiny.

Diffusion

Particles will move to fill the space available to them. They can do this in both liquids and gases. 
An example is the diffusion of bromine from one flask to another. After five minutes the bromine gas has diffused into the left-hand flask. This happens because both air and bromine particles are moving randomly and there are large gaps between the particles. The particles can therefore easily mix together.