Sandpaper Cu wire until coating is removed, heat at blue flame until red hot. cool&examine, chemical equation?

Question

Sandpaper Cu wire until coating is removed, heat at blue flame until red hot. cool&examine, chemical equation?

Answer 1

The hot copper will be oxidized by air.  You should observe a black coating on the copper wire.  Copper actually has two oxides, black CuO (cupric oxide, copper(II) oxide) and brown/red Cu2O (cuprous oxide, copper(I) oxide).  The CuO layer is flaky, and can be rubbed off.  The metal underneath should be a dull copper color - this indicates that a coating of Cu2O is also present (this adheres well to the copper surface).

The equations are:

4Cu + O2 -----> 2Cu2O

Presumably the CuO is formed by oxidation of Cu2O, not Cu metal:

2Cu2O + O2 -----> 4CuO

The net equation for copper oxidizing to CuO would thus be:

2Cu + O2 -----> 2CuO