The formation of brown fumes. Color of the solution changes to green after the metal dissolves.
name: The interaction of mercury with concentrated nitric acid
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Concentrated nitric acid is a strong oxidizing agent. Unlike regular acids which have oxidizing properties due to the presence a hydrogen cation in their molecule, a molecule of nitric acid has a nitrogen atom in oxidation state +5, which gives very strong oxidizing properties. Due to this fact, mercury, insoluble in regular acid because of its location in the electrochemical series which is to the right of hydrogen, may be oxidized and dissolved in nitric acid. The color of the solution changes to green, because of partially soluble nitrogen oxides. Fumes of the solution are composed of NO2 (brown gas).