There are two oxoacids referred to as periodic (pronounced per-iodic) or iodic (VII) acid:
1. Molecular formula: HIO4
2. Molecular formula: H5IO6, also shown as HIO4 • 2 H2O
Hydration of HIO4 gives H5IO6 and dehydration of H5IO6 gives HIO4.
The commercially available periodic acid is usually H5IO6.
Periodic acid is a strong oxidizing agent, commonly used to oxidize glycols.