Samples Containing Thorium or Uranium

The Metals

Th: The metal dissolves readily in Aqua Regia and is soluble in HCl (standard reduction potential is -1.90 volts vs N.H.E), but is not readily soluble in other non-oxidizing acids such as sulfuric acid or hydrofluoric acid. Nitric acid alone passivates the surface rendering it insoluble. The metal is not attacked by the alkali hydroxides.

U: The reduction potential is close (-1.80 volts vs N.H.E) to that of Th and so is the solubility of the metal. Metallic uranium is soluble in HCl or HNO₃ and soluble to some extent in cold dilute sulfuric acid. The caustic alkalis have no apparent action.

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