Periodic acid
chemical compound
Periodic acid ( per-eye-OD-ik) is an oxoacid of iodine. It can exist in two forms: orthoperiodic acid, with the chemical formula H5IO6, and metaperiodic acid, which has the formula HIO4. Periodic acids are colourless crystals. Periodic acid features iodine in the highest oxidation state of +7.
Periodic acid was discovered by Heinrich Gustav Magnus and C. F. Ammermüller in 1833.
Properties
Orthoperiodic acid has a number of acid dissociation constants. The pKa of metaperiodic acid has not been determined.
H5IO6 ⇌ H4IO−6 + H+, pKa1 = 3.29
H4IO−6 ⇌ H3IO2−6 + H+, pKa2 = 8.31
H3IO2−6 ⇌ H2IO3−6 + H+, pKa1 = 11.60
There being two forms of periodic acid, it follows that two types of periodate salts are formed. For example, sodium metaperiodate, NaIO4, can be synthesised from HIO4 while sodium orthoperiodate, Na5IO6 can be synthesised from H5IO6.
Structure
Orthoperiodic acid forms monoclinic crystals (space group P21/n) consisting of a slightly deformed IO6 octahedron interlinked via bridging hydrogens.
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