Copper in Concentrated Strong Acids
Pieces of copper are added to hot concentrated solutions of hydrochloric, phosphoric, sulfuric and nitric acids. A reaction clearly takes place between copper and nitric acid.
The presence of copper ions can be observed by adding each solution to a dilute solution of ammonia. If copper ions were present, we would see the blue color of the copper-ammonia complex. Sulfuric acid has oxidized the copper metal, as indicated by the blue color. Nitric acid is a stronger oxidizing agent (and produces a higher concentration of copper(II) ions), as indicated by the darker blue color.
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