Mixing of CuCl and CuCl2·2H2O
This experiment is very simple, but it effectively shows the formation of a dark complex, just by simply mixing solid copper (I) chloride and solid copper (II) chloride and adding a small amount of water.
Required chemicals:
-
copper (II) chloride, dihydrate
- copper (I) chloride
Procedure for the experiment
A spatula full of copper (I) chloride, off-white solid, is mixed with copper (II) chloride in a wet test tube. Where the solids touch each other and become wet, a very dark, almost black compound is formed. The picture below shows the white copper (I) chloride, the green/blue copper (II) chloride and the black product, formed in the reaction between the two chlorides.
When a small amount of water is added, then the liquid becomes almost black. On the glass, undissolved copper (I) chloride can still be observed in the form of small white specks.
When more water is added, then the dark compound disappears and the liquid becomes green and turbid. The turbidity is due to remaining, undissolved copper (I) chloride. The dark complex decomposes on dilution. Probably the mixed copper (I) / copper (II) / chloride complex then decomposes to plain copper (II) / chloride complex, which is green in solution and separate copper (I) / chloride complex, which is colorless in solution, or white when precipitated.
When a picture is made of the same test tube, from a viewpoint, upwards, just below the test tube, then the remaining off-white copper (I) chloride still can be seen:
Remark: Pure copper (I) chloride is completely white, like fresh snow. The copper (I) chloride, used here, is off-white. This off-white color is due to a slight impurity. Copper (I) chloride becomes off-white on storage in air, because it is oxidized a little. The oxidation product is mostly copper (II) hydroxy-chloride, CuOHCl. This slight impurity of the copper (I) chloride, however, does not affect the outcome of this experiment in a relevant way.
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