Perchloric acid

Perchloric acid

Names
Systematic IUPAC name chloric(VII) acid
Other names Hyperchloric acid
Identifiers
CAS Number	7601-90-3 Y
3D model (Jmol)	Interactive image
ChEBI	CHEBI:29221 Y
ChEMBL	ChEMBL1161634 Y
ChemSpider	22669 Y
ECHA InfoCard	100.028.648
EC Number	231-512-4
PubChem	24247
RTECS number	SC7500000
UN number	1873
InChI InChI=1S/ClHO4/c2-1(3,4)5/h(H,2,3,4,5) Y Key: VLTRZXGMWDSKGL-UHFFFAOYSA-N Y InChI=1/ClHO4/c2-1(3,4)5/h(H,2,3,4,5) Key: VLTRZXGMWDSKGL-UHFFFAOYAD
SMILES OCl(=O)(=O)=O
Properties
Chemical formula	HClO4
Molar mass	100.46 g/mol
Appearance	colorless liquid
Odor	odorless
Density	1.768 g/cm3
Melting point	−17 °C (1 °F; 256 K) (azeotrope) -112 °C (anhydrous)
Boiling point	203 °C (397 °F; 476 K) (azeotrope)
Solubility in water	miscible
Acidity (pKa)	-15.2 (±2.0); ≈ −10
Hazards
Safety data sheet	ICSC 1006
EU classification (DSD)	Oxidant (O) Corrosive (C)
R-phrases	R5, R8, R35
S-phrases	(S1/2), S23, S26, S36, S45
NFPA 704	0 3 3 OX
Related compounds
Related compounds	Hydrochloric acid Hypochlorous acid Chlorous acid Chloric acid
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Y  (what is YN ?)
Infobox references

Perchloric acid is a mineral acid with the formula HClO₄. Usually found as an aqueous solution, this colorless compound is a stronger acid than sulfuric and nitric acid. It is a powerful oxidizer when hot, but its aqueous solutions up to approximately 70% by weight at room temperature are generally safe, only showing strong acid features and no oxidizing properties. Perchloric acid is useful for preparing perchlorate salts, especially ammonium perchlorate, an important rocket fuel component. Perchloric acid is dangerously corrosive and readily forms potentially explosive mixtures.

Perchloric acid is produced industrially by two routes. The traditional method exploits the high aqueous solubility of sodium perchlorate (209 g/100 mL of water at room temperature). Treatment of such solutions with hydrochloric acid gives perchloric acid, precipitating solid sodium chloride:

The concentrated acid can be purified by distillation. The alternative route, which is more direct and avoids salts, entails anodic oxidation of aqueous chlorine at a platinum electrode.

Treatment of barium perchlorate with sulfuric acid precipitates barium sulfate, leaving perchloric acid. It can also be made by mixing nitric acid with ammonium perchlorate and boiling while adding hydrochloric acid. The reaction gives nitrous oxide and perchloric acid due to a concurrent reaction involving the ammonium ion and can be concentrated and purified significantly by boiling off the remaining nitric and hydrochloric acids.

Anhydrous perchloric acid is an unstable oily liquid at room temperature. It forms at least five hydrates, several of which have been characterized crystallographically. These solids consist of the perchlorate anion linked via hydrogen bonds to H₂O and H₃O⁺ centers 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. Thus, if left open to the air, concentrated perchloric acid dilutes itself by absorbing water from the air.