Potassium periodate

Structural formula
General
Surname	Potassium periodate
other names	Potassium metaperiodate Potassium tetroxoiodate (VII)
Molecular formula	KIO 4
Brief description	colorless and odorless solid
External identifiers / databases
CAS number 7790-21-8 EC number 232-196-0 ECHA InfoCard 100.029.269 PubChem 516896 ChemSpider 128877 Wikidata Q417125
properties
Molar mass	230.00 g · mol -1
Physical state	firmly
density	3.62 g cm −3
Melting point	582 ° C (decomposition)
solubility	5.1 g l −1 at 25 ° C in water
safety instructions
GHS labeling of hazardous substances danger H and P phrases H: 272-315-319-335 P: 210-220-221-305 + 351 + 338-405-501
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Potassium periodate is a chemical compound from the group of periodates (more precisely the potassium salt of metaperiodic acid ). It is a white, crystalline solid that dissolves relatively poorly in water.

Extraction and presentation

For representation in the laboratory, potassium iodate is used , which is oxidized with the help of potassium peroxodisulfate in an alkaline medium (expediently in potassium hydroxide solution , KOH):

${\displaystyle \mathrm {IO_{3}^{-}+S_{2}O_{8}^{2-}+2\ OH^{-}\longrightarrow IO_{4}^{-}+2\ SO_{4}^{2-}+H_{2}O} }$

The reaction is carried out in boiling solution. The salt can then be precipitated by neutralization with half-concentrated nitric acid , washed with ice water and filtered off . Another possibility is to introduce chlorine into alkaline potassium iodate solution .:

${\displaystyle \mathrm {KIO_{3}+2\ KOH+Cl_{2}\longrightarrow KIO_{4}+2\ KCl+H_{2}O} }$

properties

Potassium periodate is a powerful oxidizer . An aqueous solution of potassium iodide is oxidized by potassium periodate to elemental iodine , manganese (II) salts are oxidized to permanganates .

${\displaystyle \mathrm {KIO_{4}+2\ KI+H_{2}O\longrightarrow KIO_{3}+I_{2}+2KOH} }$

Its crystals are isomorphic with potassium perchlorate . When dissolving in potassium hydroxide solution, potassium diperiodate is formed , which can be returned to simple potassium periodate with nitric acid.

${\displaystyle \mathrm {2\ KIO_{4}+2\ KOH\longrightarrow K_{4}I_{2}O_{9}+H_{2}O} }$

${\displaystyle \mathrm {K_{4}I_{2}O_{9}+2\ HNO_{3}\longrightarrow 2KIO_{4}+2KNO_{3}+H_{2}O} }$

Potassium orthoperiodate K ₂ H ₃ IO ₆ , which is formed by the oxidation of potassium iodate with sodium hypochlorite , gives off water at 100 ° C and changes to potassium diperiodate.

${\displaystyle \mathrm {2\ K_{2}H_{3}IO_{6}\ {\xrightarrow {100^{o}C}}\ K_{4}I_{2}O_{9}+3\ H_{2}O} }$

The following equilibria exist in aqueous solutions of periodates:

${\displaystyle \mathrm {\lbrack H_{3}IO_{6}\rbrack ^{2-}+H^{+}\rightleftharpoons \lbrack IO_{4}\rbrack ^{-}+2\ H_{2}O} }$

${\displaystyle \mathrm {2\ \lbrack H_{3}IO_{6}\rbrack ^{2-}\rightleftharpoons 2\ \lbrack HIO_{5}\rbrack ^{2-}+2\ H_{2}O} }$

${\displaystyle \mathrm {2\ \lbrack HIO_{5}\rbrack ^{2-}\rightleftharpoons \lbrack H_{2}I_{2}O_{10}\rbrack ^{4-}\rightleftharpoons \lbrack I_{2}O_{9}\rbrack ^{4-}+H_{2}O} }$

use

In addition to its effect as an oxidizing agent, potassium periodate is used as a reagent for the analytical determination of cerium .

Individual evidence

1. ↑ ^{a b c d e} data sheet potassium periodate from AlfaAesar, accessed on May 15, 2017 ( PDF )(JavaScript required) .
2. ↑ Claudia Synowietz (Ed.): Paperback for chemists and physicists . founded by Jean d'Ans, Ellen Lax. 4th edition. Volume II: Organic Compounds . Springer, Berlin 1983, ISBN 3-540-12263-X .
3. ↑ G. Brauer (Ed.), Handbook of Preparative Inorganic Chemistry 2nd ed., Vol. 1, Academic Press 1963, p. 325.
4. ↑ ^{a b} C. Rammelsberg: "About the hyperiodic acid and its salts" in Ber. d. German chem. Ges. 1868 , A1 , p. 70ff. Full text
5. ^ ^{A b c d} C. E. Housecroft, AG Sharpe: "Inorganic chemistry", Pearson Education Verlag, 2005, ISBN 978-0-13-039913-7 . P. 487 ( limited preview in Google Book search)
6. ↑ # B. Brehler, H. Jacobi, H. Siebert: "crystal structure and vibrational spectrum of K4J2O9" in Journal of Polymer Science 1968 , 362 (5-6), p 301-311. doi : 10.1002 / zaac.19683620510
7. ↑ NI Nikitina, ZK Nikitina: “Thermolysis of disubstituted lithium and sodium orthoperiodates” in Russian Journal of Inorganic Chemistry 2007 , 52 (4), pp. 535-541. doi : 10.1134 / S0036023607040031
8. ^ M. Venugopalan and KJ George: "Determination of cerium by potassium periodate" in Naturwissenschaften , 43 (15), pp. 348-349. doi : 10.1007 / BF00755157