CHAPTER IVTHE NON-METALLIC ELEMENTS IN BINARY
COMPOUNDSOne of the distinctive chemical properties of non-metallic
elements is their ability to combine with metals forming simple
binary compounds in which they are the negative constituent.
It is the purpose of this chapter to deal with such simple com-
pounds of the more pronounced non-metals: chlorine, bromine,
iodine, oxygen, sulphur, and nitrogen.
PREPARATION 5
COPPER OXIDE, CUO
The most obvious method of making a metal oxide is to heat the
metal in air or oxygen, but the difficulty with such a method is that
the oxide is solid and adheres to the surface, preventing the action
on the metal underneath. Better results are obtained if an oxy-
salt of the metal is prepared and then heated to a sufficient tem-
perature to drive off the non-metal oxide and thus leave the oxide
of the metal as a residue. Carbonates, nitrates, and some sulfates
can be decomposed in this way.
Dilute nitric acid attacks copper, forming copper nitrate, a
soluble salt, so that the surface of the metal remains free until
the copper has all reacted. Copper oxide may be obtained by
heating the solution, first to expel the water, and then with a
somewhat stronger heat to decompose the residue of copper
nitrate; oxides of nitrogen escape as red fumes, and copper oxide
remains as a black solid. This is the method by which zinc was
converted quantitatively into zinc oxide, page 24.
Since copper carbonate decomposes at a lower temperature than
copper nitrate and yields an impalpable powder instead of black
crusts, it is advantageous in this preparation to first precipitate
copper carbonate (actually a basic carbonate) from the copper
nitrate solution and after drying it, to heat the carbonate.
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