HIO

HIO may refer to:

Iodic acid

Iodic acid, HIO₃, can be obtained as a white or off-white solid. It dissolves in water very well, but it also exists in the pure state, as opposed to chloric acid or bromic acid. Iodic acid contains iodine in the oxidation state +5 and it is one of the most stable oxo-acids of the halogens in its pure state. When iodic acid is carefully heated, it dehydrates to iodine pentoxide. On subsequent heating, the iodine pentoxide further decomposes, giving a mix of iodine, oxygen and lower oxides of iodine.

Preparation

Iodic acid can be produced by oxidizing I₂ with strong oxidizers such as Nitric acid HNO
3, Chlorine Cl
2, Chloric acid HClO
3 or Hydrogen peroxide H
2O
2, for example :

Properties

Iodic acid is a relatively strong acid with a pK_a of 0.75. It is strongly oxidizing in acidic solution, less so in basic solution. When iodic acid acts as oxidizer, then the product of the reaction is either iodine, or iodide ion. Under some special conditions (very low pH and high concentration of chloride ion, e.g. in concentrated hydrochloric acid), iodic acid is reduced to iodine trichloride, a golden yellow compound in solution and no further reduction occurs. In the absence of chloride ions, when there is an excess amount of reductant, then all iodate is converted to iodide ion. When there is an excess amount of iodate, then part of the iodate is converted to iodine.

Periodic acid

Periodic acid (pronounced per-iodic /ˌpɜːr.aɪˈɒdᵻk/ PURR-eye-OH-dik, rather than /ˌpɪərɪˈɒdᵻk/ PEER-ee-OD-ik as in periodic table) is the highest oxoacid of iodine, in which the iodine exists in oxidation state VII. Like all periodates it can exist in two forms: orthoperiodic acid, with the chemical formula H₅IO₆ and metaperiodic acid, which has the formula HIO₄.

Periodic acid was discovered by Heinrich Gustav Magnus and C. F. Ammermüller in 1833.

Synthesis

Modern industrial scale production involves the electrochemical oxidation of iodic acid, on a PbO₂ anode, with the following standard electrode potential:

Orthoperiodic acid can be dehydrated to give metaperiodic acid by heating to 100 °C

Further heating to around 150 °C gives Iodine pentoxide (I₂O₅) rather than the expected anhydride diiodine heptoxide (I₂O₇). Metaperiodic acid can also be prepared by from various orthoperiodates by treatment with dilute nitric acid.

Properties

Orthoperiodic acid has a number of acid dissociation constants. The pKa of meta periodic acid has not been determined.