Overview

Selenic acid is the inorganic oxoacid of selenium with the formula H2SeO4. In this compound selenium is in its highest common oxidation state (+6). Selenic acid is the selenium analogue of sulfuric acid and is most commonly encountered as a concentrated aqueous solution. It behaves as a strong acid and an oxidizing agent and is the parent compound for the selenate anion (SeO4(2-)).

Characteristics and reactions

Pure selenic acid is typically a colorless, hygroscopic substance that dissolves readily in water. Chemically it donates protons like other strong acids and forms salts called selenates on neutralization. As an oxidizer it can convert various reducing substances to higher oxidation states and may react vigorously with organic matter, metals, and other reductants. On heating or under strongly reducing conditions it can decompose to lower selenium oxides and release oxygen.

Preparation and uses

Selenic acid is prepared in the laboratory by oxidizing lower selenium oxides or selenous acid (H2SeO3) with suitable oxidants. Its principal uses are as a reagent to synthesize selenate salts, to introduce selenium in higher oxidation states in chemical syntheses, and in analytical chemistry where selenate species are relevant. Derivatives such as sodium and potassium selenate are more commonly used in industry and research than the free acid.

Safety, environmental and distinguishing points

Selenic acid is corrosive and its compounds are toxic; selenium compounds can be hazardous to humans and wildlife in excess. Handling requires standard precautions for strong oxidizers and strong acids. It should be distinguished from selenous acid (H2SeO3), which contains selenium in the +4 state and has different reactivity, and from sulfuric acid, to which it is chemically analogous but not identical in behavior.

Further information

  • Common reactions: neutralization to selenates, oxidative conversions.
  • Laboratory note: often stored and used as aqueous solutions rather than the neat acid.
  • Reference entry: see chemical databases and reagent suppliers for material safety data and handling guidance.