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

Key definitions:

Dilution is the effect of placing a substance into a solvent and decreasing its concentration, e.g. adding 10cm³ of water to 10cm³ of 1 mol/dm³ hydrochloric acid, will turn the acid's concentration to 0.5 mol/dm³

Diffusion is the movement of particles from an area of high concentration to an area of low concentration. This only occurs in a fluid (gas or liquid)

Experiment 1 (dilution):

Take a beaker with 10cm³ of water containing any colour of food colouring. Then add another 10cm³ of non-coloured water to the beaker. The coloured water will dilute and hence the colour of the water will become lighter.

Experiment 2 (diffusion):

A piece of cotton soaked with HCL is placed at one end of a tube while another piece of cotton is soaked with ammonia (NH3) and is placed on the other side of the tube. The tube is then sealed. You will observe a white ring (ammonium chloride) form near the end of the cotton soaked in HCL. This is because the NH3 molecules have a relative atomic mass of 17 while the molecules of HCL have a relative atomic mass of 36.5; i.e. the molecules of ammonia are lighter than those of HCL.