Question

You could have noticed that when copper powder is heated in a china dish the surface of the copper powder becomes coated with black colour substance 1) Why has this black coloured substance formed? 2) What is that black substance? 3) Write chemical equation of the reaction

Answer 1

The black coloured substance is copper oxide. It has formed due to reaction of copper with oxygen.

Cu+O2 = CuO

Answer 2

1) A black colored substance of copper (II) oxide is formed when the “copper powder” is heated in a ‘china dish’.

Upon heating, the copper reacts with the oxygen present in air and forms copper (II) oxide, which is black in colour. This process is called surface oxidation.

As the copper melts, it changes its colour gradually and finally turns black on the surface. The rate of copper (II) oxide formation depends upon the temperature and the wavelength of copper.  

2) The black substance is copper (II) oxide

3) Chemical equation:

$2 C u(s)+O_{2}(g) \rightarrow 2 C u O(s)$

$Copper + oxygen \rightarrow copper (II) oxide$