Overview
Iodate is the polyatomic ion with formula IO3-. The central iodine atom is in the +5 oxidation state, giving the species characteristic chemical behavior that differs from lower (iodide) and higher (periodate) iodine oxyanions. Iodates are commonly encountered as crystalline salts and as reactive species in solution.
Structure and properties
The iodate ion has three oxygen atoms bonded to iodine and a lone pair on the central atom; resonance structures distribute the negative charge over the oxygens. Its idealised molecular geometry is often described as a trigonal pyramidal arrangement, similar in shape and bonding to other halogen oxoanions such as the chlorates. Iodate salts are generally oxidizing agents (less strongly oxidizing than periodates) and show moderate solubility depending on the counterion. Many iodates are stable solids at room temperature.
Preparation and chemical reactions
Iodates can be produced by controlled reduction of periodate (IO4−) or by oxidation of iodides under suitable conditions; the conversion from periodate by reduction is a convenient laboratory route. In acidic solution iodate reacts with acids to form iodic acid (HIO3) and, in presence of excess iodide and acid, iodate oxidizes iodide to molecular iodine. A well-known stoichiometric reaction is: IO3- + 5 I- + 6 H+ → 3 I2 + 3 H2O This reaction underlies several iodometric and redox titration methods. Iodates are formally the salts of iodic acid; for example, sodium iodate is written as NaIO3 (sodium iodate).
Uses and occurrence
Iodates have practical roles in analytical chemistry as oxidants and titrants and are used as stable iodine sources for food fortification; for instance, potassium iodate is chosen in some salt iodization programs because it resists oxidation better than iodide. Iodate compounds also appear in inorganic synthesis and in studies of iodine cycling in environmental and marine chemistry, where they influence the speciation and mobility of iodine in water.
Safety and notable facts
As oxidizing salts, iodates should be stored away from reducing agents and combustible materials. Many iodate salts are handled routinely in laboratories, but ingestion or inhalation of powders should be avoided. Historically, the discovery and classification of iodate and related oxyanions helped establish early concepts of oxidation states and halogen chemistry.
- Typical ion: IO3- (ion).
- Iodine oxidation state: +5.
- Related species: periodate and iodic acid (HIO3).
- Example salt: sodium iodate; see also salts used for iodization.
For more technical details and reference data consult standard inorganic chemistry sources or specialized databases (ion terminology and definitions, oxidation state summaries at +5 oxidation state entries, and reagent notes for reductions and oxidations at reduction and periodate resources).