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Why does mercury in dilute HNO3 give mercurous nitrate while hot concentrated HNO3 produces mercuric nitrate? “Mercury dissolves in oxidizing acids, producing either Hg${^{2+}}$ or Hg$_2$$^{2+}, depending on which reagent (mercury or e.g., nitric acid) is in excess.” Ref 1 Wikipedia says “Mercuric nitrate can be reacted with elemental mercury to form ... 2 In solution, nitric acid \ce{HNO3} reacts with water to form the ions \ce{H3O+} and \ce{NO3^-}. None of these ions have a redox potential high enough to oxidize noble metals like silver or metallic mercury. When pure, the same nitric acid \ce{HNO3} takes part to an equilibrium$$\ce{3 HNO3 <=> NO2^+ + H3O+ + 2 NO3-}$$And here something new ... 1 One likely possible meaning of USFDA is United States Food and Drug Administration, since «The United States Food and Drug Administration (FDA or USFDA) is a federal agency of the Department of Health and Human Services. The FDA is responsible for protecting and promoting public health through the control and supervision of food safety, tobacco products, ... 1 Based on Red Book's 4-page summary (vide infra), I suggest to proceed with these steps: What is the central ion? It is cobalt(IV). What are the ligands: a nitrite (then to be called nitrido), four chlorides (then to be called chlorido) and a thiocyanate. According to your drawing, the later binds to$\ce{Co}\$ via sulfur, thus named with the kappa notation ...