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Some compounds of metals are soluble in various solutions. These metals can be dissolved from a finely ground rock, and the solution with the metal compound can be recovered for further processing.
Here, cupric sulfate pentahydrate (CuSO4. 5H2O) is mixed with finely ground rock or dirt. Cupric sulfate is soluble in water, so this is leached from the rock mixture with water. The water is collected in a plate for further study. Interferences can include other compounds in the dirt mixture which are also water-soluble.
This step depends on the relative solubilities of the cupric sulfate and rock in water. If cupric sulfate were not soluble in water, different solution would have to be used to leach the cupric sulfate from the rock mixture.
The copper is separated from the solution by precipitating the copper metal on an iron paper clip. (Reduction of the cupric ion in solution to copper metal and oxidation of the iron paper clip to ferrous sulfate in solution.) The reaction can be written:
CuSO4 (aq) + Fe (s) ® Cu (s) + FeSO4 (aq), or
Cu+2(aq) + Fe (s) ® Cu (s) + Fe+2(aq)
The paper clips need to be only iron, not nickel coated. Steel wool can be used also.
Not only does the paper clip become the characteristic copper color, but also the blue color of the copper ion in solution disappears from the solution, indicating that the copper ion (Cu+2) has been removed from solution.
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