por What is potassium iodate?
Potassium iodate or potassium iodate is an inorganic iodine compound, specifically a salt, whose chemical formula is KIO3. Iodine or iodine, an element from the halogen group (F, Cl, Br, I, As), has an oxidation number of +5 in this salt; for this reason it is a strong oxidizing agent. KIO3 dissociates in aqueous medium to create K+ and IO3– ions.
It is synthesized by reacting potassium hydroxide with iodic acid: HIO3(aq) + KOH(s) => KIO3(aq) + H2O(l). Also, it can be synthesized by reacting molecular iodine with potassium hydroxide: 3I2(s) + 6KOH(s) => KIO3(aq) + 5KI(aq) + 3H2O(l).
Potassium Iodate Properties
It is an odorless white solid, with fine crystals and a monoclinic crystalline structure. It has a density of 3.98 g/mL, a molecular weight of 214 g/mol, and has absorption bands in the infrared (IR) spectrum.
It has a melting point: 833 ºK (560 ºC), consistent with the strong ionic interactions between the K+ and IO3– ions. At higher temperatures it undergoes a thermal decomposition reaction, releasing molecular oxygen and potassium iodide:
2KIO3(s) => 2KI(s) + 3O2(g)
In water, it has solubilities that vary from 4.74g/100mL at 0ºC, up to 32.3g/100mL at 100ºC, generating colorless aqueous solutions. Also, it is insoluble in alcohol and nitric acid, but it is soluble in dilute sulfuric acid.
Its affinity for water is not appreciable, which explains why it is not hygroscopic and does not exist in the form of hydrated salts (KIO3·H2O).
Oxidizing agent
Potassium iodate, as indicated by its chemical formula, has three oxygen atoms. This is a strongly electronegative element and, due to this property, leaves an electronic deficiency “uncovered” in the cloud surrounding the iodine.
This deficiency —or contribution, as the case may be— can be calculated as the oxidation number of iodine (±1, +2, +3, +5, +7), being +5 in the case of this salt.
What does this mean? That before a species capable of giving up its electrons, iodine will accept them in its ionic form (IO3–) to become molecular iodine and have an oxidation number equal to 0.
Following this explanation it can be determined that potassium iodate is an oxidizing compound that reacts intensely with reducing agents in many redox reactions; Of all these, one is known as the iodine clock.
The iodine clock consists of a slow and fast step redox process, in which the fast steps are marked by a KIO3 solution in sulfuric acid to which starch is added. Next, starch —once species I3 is produced and anchored within its structure—— will turn the solution from colorless to dark blue.
IO3− + 3 HSO3− → I− + 3 HSO4−
IO3− + 5 I− + 6 H+ → 3 I2 + 3 H2O
I2 + HSO3− + H2O → 2 I− + HSO4− + 2 H+ (dark blue due to starch effect)
chemical structure
The chemical structure of potassium iodate is illustrated in the image above. The IO3– anion is represented by the “tripod” of red and purple spheres, while the K+ ions are represented by the purple spheres.
But what do these tripods mean? The correct geometric shapes of these anions are actually trigonal pyramids, in which the oxygens make up the triangular base, and the iodine lone pair of electrons points up, taking up space and forcing the I–O bond to bend downward and the two I=O links.
This molecular geometry corresponds to an sp3 hybridization of the central iodine atom; however, another perspective suggests that one of the oxygen atoms forms bonds with the «d» orbitals of iodine, actually being a sp3d2 type hybridization (iodine can dispose of its «d» orbitals by expanding its valence shell).
The crystals of this salt can undergo structural phase transitions (other than monoclinic arrangements) as a consequence of the different physical conditions that they are subjected to.
Potassium Iodate Uses and Applications
Therapeutic use
Potassium iodate is usually used to prevent the accumulation of radioactivity in the thyroid in the form of 131I, when this isotope is used to determine iodine uptake by the thyroid as a component of thyroid gland function.
Similarly, potassium iodate is used as a topical antiseptic (0.5%) in mucosal infections.
use in industry
It is added to farm animal feed as an iodine supplement. Therefore, in the industry potassium iodate is used to improve the quality of flours.
analytical use
In analytical chemistry, thanks to its stability, it is used as a primary standard in the standardization of sodium thiosulfate (Na2S2O3) standard solutions, with the purpose of determining iodine concentrations in problem samples.
This means that the amounts of iodine can be known by volumetric techniques (titrations). In this reaction, potassium iodate rapidly oxidizes iodide ions I–, using the following chemical equation:
IO3– + 5I– + 6H+ => 3I2 + 3H2O
Iodine, I2, is titrated with the Na2S2O3 solution for standardization.
Use in laser technology
Studies have demonstrated and corroborated the interesting piezoelectric, pyroelectric, electro-optical, ferroelectric and non-linear optical properties of KIO3 crystals. This results in great potential in the electronic field and in laser technology for materials made from this compound.
Potassium Iodate Health Risks
In high doses it can cause irritation to the oral mucosa, skin, eyes and respiratory tract.
Experiments on the toxicity of potassium iodate in animals have made it possible to observe that in fasting dogs, at doses of 0.2-0.25 g/kg of body weight, administered orally, the compound causes vomiting.
If these vomits are avoided, it produces a worsening of their situation in the animals, since anorexia and prostration prior to death are induced. Their autopsies allowed us to observe necrotic lesions in the liver, kidneys and intestinal mucosa.
Due to its oxidizing power, it represents a fire risk when in contact with flammable materials.
References
Day, R., & Underwood, A. Quantitative Analytical Chemistry (fifth ed.). PEARSON Prentice Hall, p-364.
ChemicalBook. (2017). Potassium iodate. Retrieved on March 25, 2018, from ChemicalBook: chemicalbook.com
PubChem. (2018). Potassium Iodate. Retrieved on March 25, 2018, from PubChem: pubchem.ncbi.nlm.nih.gov
Merck. (2018). Potassium iodate. Retrieved on March 25, 2018, from Merck:
merckmillipore.com
MM Abdel Kader et al. (2013). Charge transport mechanism and low temperature phase transitions in KIO3. J. Phys.: Conf. Ser. 423 012036