Heating a Copper Envelope

7 Experiments on Substances and Their Properties E3.1 Heating a Copper Envelope 

Problem This experiment demonstrates that copper does not change color from red-brown to black, but rather that a black substance always develops when air is present copper reacts with oxygen in the air, forming black copper oxide. If no air is available in the inside of the closed metal envelope, then the red-brown copper remains nearly unchanged. 

Material Crucible tongs, burner sheet of copper metal. 

Procedure Fold a sheet of copper metal in half. Fold again and press together with crucible tongs the open sides of the sheet. Heat this envelop in a hot burner flame for 10 20 s. Cool the envelop and unfold it. Compare the inner and outer parts. 

Observation The outer side of the red-brown metal envelope turns black upon heating copper oxide. The black substance separates and falls off upon unfolding the envelope, on the inside of the envelope only red-brown copper is to be seen, no black substance. 

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