When directly heated, copper will form a layer of copper oxide on its surface. When left in air, the copper reacts with oxygen very slowly. By folding an envelope shape from the copper foil we can make sure the inside is inaccessible to air. When heated and unfolded, the inside and outside can be compared. The outside surface should show a layer of copper oxide whereas the inside should remain relatively unchanged.
Equipment required (per set):
The copper foil square should be folded into an envelope shape (see Fig 1), held in the tongs and directly heated in the blue Bunsen flame for five minutes or so.
- Copper foil (no more than 5cm²)
- Bunsen burner
- Heatproof mat
The copper envelope should be left to cool for several minutes on a heatproof mat.
When cool, the envelope can be opened and the surfaces compared.