Oxidation and reduction of copper

A piece of copper metal is heated in a flame and oxidized to black copper oxide by air. The oxidized copper is reduced when placed in a hydrogen atmosphere. When removed from the hydrogen atmosphere, the metal is again oxidized.

Reaction of sodium and chlorine

A small piece of sodium metal is placed in a flask containing chlorine gas. Initially, no reaction is observed, but addition of a drop of water to the sodium initiates a vigorous reaction. Includes close-up replay of reaction.