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• Osmosis

Diffusion is the movement of molecules from a region of high concentration to one of low concentration. If you have ever opened a bottle of cologne or perfume, you have witnessed diffusion. Molecules of the scent escape from the container, where they are present in very high concentration. They spread outward in every direction to regions where they are in low concentration. Your nose is able to detect the smell of the cologne or perfume even if you are quite a distance from the bottle that has been opened.

Diffusion occurs in all states of matter: solid, liquid, and gas. It occurs rapidly enough to be observable in a reasonable period of time, however, only in liquids and gases.

You can demonstrate diffusion easily in your home. Fill a glass with water. Then add 10 drops of ink (any color) to the water very carefully. The ink sinks to the bottom of the glass because it is...