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This is a colorful and estatically pleasing experiment.  Colors ranging from...
  • the blues of Cu(H2O)62+
  • the green of CuCl2(H2O)4
  • to the brown of CuCl4-2

are shown by  Copper(II) compounds.

This contrasts with the pale yellows and whites of Copper(I) compounds....
Copper is a transition element. These colors reflect the d9 electron configuration of Cu(II) and the d10 configuration of Cu(I).


This synthesis starts with copper metal which is converted to the nitrate by reaction with concentrated Nitric Acid.

This equation is not balanced
Cu + HNO3--> Cu(NO3)2 + H2O +NO2

Please balance this redox reaction.
If worse gets to worse, see your Lab Manual
Why is Nitric acid rather than Hydrochloric acid used in this step?


This copper(II) nitrate needs to be converted to copper(II) chloride which is then reduced to the desired copper(I) chloride.
This is done by first precipitating the copper(II) as copper carbonate and then dissolving in an excess of HCl.

Cu(NO3)2 + Na2CO3 ------> CuCO3 + 2 NaNO3

CuCO3 + 2 HCl -----> CuCl2 + CO2 + H2O

The green Copper(II) Chloride is converted to the dark brown tetrachlorocuprate(II) ion with excess Hydrochloric Acid and reduced with copper metal to a pale yellow copper(I) chloro complex.

CuCl4-2 + Cu -----> 2 CuCl3-2

The color of the solution shows the degree of reaction

The above transitions happen in the course of 15 to 30 minutes.

Finally the product is obtained by diluting the copper(I) chloro complexes with ice and water.

Some Questions

a. Why does dilution result in the precipitation of CuCl?
b. Why is the copper(II) nitrate converted first to the carbonate and then to cupric chloride? Why not go direct?
c. This reaction is described in your Manual as "significantly affecting your every day life". HOW?
Think about the ANSWERS

RWK 1/98