Perchloric acid
From Wikipedia, the free encyclopedia
| Perchloric acid | |
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| Identifiers | |
| CAS number | 7601-90-3  |
| EC number | 231-512-4 |
| UN number | 1873 |
| RTECS number | SC7500000 |
| Properties | |
| Molecular formula | HClO4 |
| Molar mass | 100.46 g/mol |
| Appearance | colorless liquid |
| Density | 1.67 g/cm3 |
| Melting point | |
| Boiling point |
203 C (azeotrope)[3] |
| Solubility in water | miscible |
| Hazards | |
| MSDS | ICSC 1006 |
| EU Index | 017-006-00-4 |
| EU classification | Oxidant (O) Corrosive (C) |
| R-phrases | R5, R8, R35 |
| S-phrases | (S1/2), S23, S26, S36, S45 |
| NFPA 704 |
 0
3
3
OX
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| Related compounds | |
| Related compounds | Hydrochloric acid Hypochlorous acid Chlorous acid Chloric acid |
| (what is this?) (verify) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) |
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| Infobox references | |
Perchloric acid, HClO4, is an oxoacid of chlorine and is a colorless liquid soluble in water. It is a strong acid comparable in strength to sulfuric and nitric acids. It is useful for preparing perchlorate salts, but it is also dangerously corrosive and readily forms explosive mixtures.
Contents |
[edit] Production
Perchloric acid is produced by treatment of sodium perchlorate with sulfuric acid and by the electrochemical oxidation of aqueous chlorine.[4]
[edit] Acidity
Perchloric acid is a superacid, and one of the strongest Brønsted-Lowry acids. Its pKa is −10.[5]
Anhydrous perchloric acid is an oily liquid. It forms a series of at least five hydrates, several of which have been characterized crystallographically. The dihydrate is representative: the solid consists of the perchlorate anion linked to H2O and H3O+ centers via hydrogen bonds.[6] Perchloric acid forms an azeotrope with water, consisting of about 72.5% perchloric acid. This form of the acid is stable indefinitely and is commercially available. Such solutions are hygroscopic, that is, if left unsealed, concentrated acid dilutes itself by absorbing water from the air.
[edit] Laboratory preparation
The concentrated acid can be prepared by distillation of a solution of sodium perchlorate in concentrated sulfuric acid.
- NaClO4 + H2SO4 → NaHSO4 + HClO4
In a related method, barium perchlorate reacts with dilute sulfuric acid to precipitate barium sulfate, leaving perchloric acid. It also can be made by mixing nitric acid with ammonium perchlorate. The reaction gives nitrous oxide and perchloric acid due to a concurrent reaction involving the ammonium ion.
[edit] Safety
Anhydrous and monohydrated perchloric acid are explosive, but the usual aqueous solutions are stable in the absence of organic compounds. It is very corrosive to skin and eyes. Upon contact with perchloric acid, organic materials such as cloth and wood ignite. Salts of perchloric acid are also powerful oxidizers that can be explosive. Perchlorate salts tend to be more stable than their chlorate counterparts, which has led to their increased use in pyrotechnic compositions due to safety concerns.
Due to these hazards, perchloric acid is usually handled under fume hoods with wash-down and air scrubbing capabilities that are not available on standard laboratory fume hoods. The crystalline form of the acid, which is explosive and shock sensitive, can precipitate on hood surfaces; washing down the hood interior returns any crystalline form to solution, thus eliminating the explosion hazard.
[edit] References
- ^ Safety data for concentrated perchloric acid, ca. 70% msds.chem.ox.ac.uk
- ^ [http://www.geocities.com/lllwolly/further/kirkperc.pdf PERCHLORIC ACID AND PERCHLORATES] source?
- ^ Handling of Perchloric acid] ameslab.gov
- ^ Helmut Vogt, Jan Balej, John E. Bennett, Peter Wintzer, Saeed Akbar Sheikh, Patrizio Gallone "Chlorine Oxides and Chlorine Oxygen Acids" in Ullmann's Encyclopedia of Industrial Chemistry 2002, Wiley-VCH, Weinheim. Published online: 15 June, 2000
- ^ Kathleen Sellers; Katherine Weeks; William R. Alsop; Stephen R. Clough; Marilyn Hoyt; Barbara Pugh (2006). Perchlorate: environmental problems and solutions. CRC Press. p. 16. ISBN 0849380812.
- ^ Almlöf, Jan; Lundgren, Jan O.; Olovsson, Ivar "Hydrogen Bond Studies. XLV. Crystal structure of perchloric acid 2.5 hydrate" Acta Crystallographica Section B: Structural Crystallography and Crystal Chemistry 1971, 27, pp. 898-904.
