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There are mainly two forms of existence: HlO4 is known as metahioidic acid, while H5IO6 is called orthohioidic acid. Their molecular structures are as follows: At 25°C, in aqueous solution, hioidic acid exists primarily in the form of the metahioidate ion (IO4-), whereas in strongly acidic solutions it exists mainly as H5IO6. H5IO6 is a colorless crystal, a dihydrate of HIO4; upon heating in a vacuum to lose water, it can produce pyroiodic acid or transform into metahydrogen iodate. Periodic acid is a pentagonal weak acid, (K1=5.1×10-4, K2=4.9×10-9, K3=2.5×10-32); its acidity is much weaker than that of perchloric and perbromic acids, and it typically forms acid salts when reacting with bases. Periodic acid has a stronger oxidizing power than perchloric acid. It usually reacts rapidly and smoothly; in acidic media, it can oxidize Mn2+ to MnO4-. The reaction is as follows: Mn2+ + 5H5IO6 = 2MnO4- + 5IO3- + 7H2O + 11H+. Periodic acid can be prepared by reacting sulfuric acid with barium periodicate, or by using hydrochloric acid with silver periodicate. Ba5(IO6)2 + 5H2SO4 = 5BaSO4 + 2H5IO6. Periodic acid is industrially produced by electrolyzing concentrated periodic acid solutions at low temperatures. Periodic acid can oxidize organic compounds with ortho-hydroxyl groups to form small molecular carbonyl compounds, and it can be used in organic chemistry to determine the structure of ortho-polyhydroxy compounds.