1.4 describe and explain experiments to investigate the small size of particles and their movement including:

Atoms

i)          dilution of coloured solutions

If a coloured solution is introduced carefully to the bottom of a jar of water (with a pipette), it will take many days for the coloured solution to be evenly distributed throughout the jar.

If crystals of a coloured solid are put in the bottom of a jar of water, they will dissolve, and then take many days to be evenly distributed, as described above.

ii)         diffusion experiments

A gas jar of bromine will diffuse into a gas jar full of air placed on top of it. This is quicker than liquids diffusing – gas particles are more spread out and move faster. Gases diffuse into a vacuum instantly – there are no air particles to hinder their progress.

If cotton wool plugs, soaked in concentrated hydrochloric acid and concentrated ammonia solution are placed at either end of a long tube, hydrogen chloride gas and ammonia gas diffuse along the tube. Where they meet, a white ring of ammonium chloride solid is seen. This is formed closer to the hydrochloric acid end than the ammonia solution end. This shows that ammonia molecules diffuse

faster than hydrogen chloride molecules. This is because they are lighter.