Perchloric acid

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Perchloric acid
Perchloric acid
Hydroxidotrioxidochlorine Perchloric-acid-2D-dimensions.png
Perchloric acid
Hydroxidotrioxidochlorine
Perchloric acid
ydroxidotrioxidochlorine Perchloric-acid-3D-vdW.png
Perchloric acid
ydroxidotrioxidochlorine
Perchloric acid 60 percent.jpg
Names
Systematic IUPAC name
Perchloric acid
Other names
Hyperchloric acid [1]
Identifiers
3D model (JSmol)
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard 100.028.648 OOjs UI icon edit-ltr-progressive.svg
EC Number
  • 231-512-4
PubChem CID
RTECS number
  • SC7500000
UNII
UN number 1873
  • InChI=1S/ClHO4/c2-1(3,4)5/h(H,2,3,4,5) Yes check.svgY
    Key: VLTRZXGMWDSKGL-UHFFFAOYSA-N Yes check.svgY
  • InChI=1/ClHO4/c2-1(3,4)5/h(H,2,3,4,5)
    Key: VLTRZXGMWDSKGL-UHFFFAOYAD
  • O[Cl+3]([O-])([O-])[O-]
Properties
HClO4
Molar mass 100.46 g/mol
Appearancecolorless liquid
Odor odorless
Density 1.768 g/cm3
Melting point −17 °C (1 °F; 256 K) (72% aqueous solution) [2]
−112 °C (anhydrous)
Boiling point 203 °C (397 °F; 476 K) (azeotrope) [2]
Miscible
Acidity (pKa)−15.2 (±2.0); [3] ≈ −10
Conjugate base Perchlorate
Hazards
Occupational safety and health (OHS/OSH):
Main hazards
Powerful oxidizer, highly corrosive
GHS labelling:
GHS-pictogram-rondflam.svg GHS-pictogram-acid.svg GHS-pictogram-exclam.svg GHS-pictogram-silhouette.svg
Danger
H271, H290, H302, H314, H373
P210, P280, P303+P361+P353, P304+P340, P305+P351+P338, P310, P371, P375, P380
NFPA 704 (fire diamond)
NFPA 704.svgHealth 3: Short exposure could cause serious temporary or residual injury. E.g. chlorine gasFlammability 0: Will not burn. E.g. waterInstability 3: Capable of detonation or explosive decomposition but requires a strong initiating source, must be heated under confinement before initiation, reacts explosively with water, or will detonate if severely shocked. E.g. hydrogen peroxideSpecial hazard OX: Oxidizer. E.g. potassium perchlorate
3
0
3
OX
Flash point Non-flammable
Safety data sheet (SDS) ICSC 1006
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).
Yes check.svgY  verify  (what is  Yes check.svgYX mark.svgN ?)

Perchloric acid is a mineral acid with the formula H Cl O 4. Usually found as an aqueous solution, this colorless compound is a stronger acid than sulfuric acid, nitric acid and hydrochloric acid. It is a powerful oxidizer when hot, but 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. [4]

Contents

History

Perchloric acid was first synthesized (together with potassium perchlorate) by Austrian chemist Friedrich von Stadion  [ de ] and called "oxygenated chloric acid" in mid-1810s. French pharmacist Georges-Simon Serullas introduced the modern designation along with discovering its solid monohydrate (which he, however, mistook for an anhydride). [5]

Production

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:

NaClO4 + HCl → NaCl + HClO4

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. [6] [7]

Laboratory preparations

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.

Properties

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. [8] An example is hydronium perchlorate. 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.

Dehydration of perchloric acid gives the anhydride dichlorine heptoxide: [9]

2 HClO4 + P4O10 → Cl2O7 + H2P4O11

Uses

Perchloric acid is mainly produced as a precursor to ammonium perchlorate, which is used in rocket fuel. The growth in rocketry has led to increased production of perchloric acid. Several million kilograms are produced annually. [6] Perchloric acid is one of the most proven materials for etching of liquid crystal displays and critical electronics applications as well as ore extraction and has unique properties in analytical chemistry. [10] Additionally it is a useful component in etching of chrome. [11]

As an acid

Perchloric acid, a superacid, is one of the strongest Brønsted–Lowry acids. That its pKa is lower than −9 is evidenced by the fact that its monohydrate contains discrete hydronium ions and can be isolated as a stable, crystalline solid, formulated as [H3O+][ClO
4
]. [12] The most recent estimate of its aqueous pKa is −15.2±2.0. [3] It provides strong acidity with minimal interference because perchlorate is weakly nucleophilic (explaining the high acidity of HClO4). Other acids of noncoordinating anions, such as fluoroboric acid and hexafluorophosphoric acid are susceptible to hydrolysis, whereas perchloric acid is not. Despite hazards associated with the explosiveness of its salts, the acid is often preferred in certain syntheses. [13] For similar reasons, it is a useful eluent in ion-exchange chromatography.

It is also used for electropolishing or etching of aluminium, molybdenum, and other metals.

Safety

Given its strong oxidizing properties, perchloric acid is subject to extensive regulations as it can react violently with metals and flammable substances such as wood, plastics, and oils. [14] Work conducted with perchloric acid must be conducted in fume hoods with a wash-down capability to prevent accumulation of oxidisers in the ductwork.

On February 20, 1947 in Los Angeles, California, 17 people were killed and 150 injured in the O'Connor Plating Works disaster. A bath, consisting of over 1000 litres of 75% perchloric acid and 35% acetic anhydride by volume which was being used to electro-polish aluminium furniture, exploded. Organic compounds were added to the overheating bath when an iron rack was replaced with one coated with cellulose acetobutyrate (Tenit-2 plastic). A few minutes later the bath exploded. [15] [16] The O'Connor Electro-Plating plant, 25 other buildings, and 40 automobiles were destroyed, and 250 nearby homes were damaged.

See also

Related Research Articles

<span class="mw-page-title-main">Acid</span> Chemical compound giving a proton or accepting an electron pair

An acid is a molecule or ion capable of either donating a proton (i.e. hydrogen ion, H+), known as a Brønsted–Lowry acid, or forming a covalent bond with an electron pair, known as a Lewis acid.

<span class="mw-page-title-main">Acid–base reaction</span> Chemical reaction between an acid and a base

In chemistry, an acid–base reaction is a chemical reaction that occurs between an acid and a base. It can be used to determine pH via titration. Several theoretical frameworks provide alternative conceptions of the reaction mechanisms and their application in solving related problems; these are called the acid–base theories, for example, Brønsted–Lowry acid–base theory.

<span class="mw-page-title-main">Chlorine</span> Chemical element, symbol Cl and atomic number 17

Chlorine is a chemical element; it has symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between them. Chlorine is a yellow-green gas at room temperature. It is an extremely reactive element and a strong oxidising agent: among the elements, it has the highest electron affinity and the third-highest electronegativity on the revised Pauling scale, behind only oxygen and fluorine.

<span class="mw-page-title-main">Ammonium perchlorate</span> Chemical compound

Ammonium perchlorate ("AP") is an inorganic compound with the formula NH4ClO4. It is a colorless or white solid that is soluble in water. It is a powerful oxidizer. Combined with a fuel, it can be used as a rocket propellant called ammonium perchlorate composite propellant. Its instability has involved it in a number of accidents, such as the PEPCON disaster.

<span class="mw-page-title-main">Aqua regia</span> Mixture of nitric acid and hydrochloric acid in a 1:3 molar ratio

Aqua regia is a mixture of nitric acid and hydrochloric acid, optimally in a molar ratio of 1:3. Aqua regia is a fuming liquid. Freshly prepared aqua regia is colorless, but it turns yellow, orange or red within seconds from the formation of nitrosyl chloride and nitrogen dioxide. It was named by alchemists because it can dissolve the noble metals gold and platinum, though not all metals.

An acidic oxide is an oxide that either produces an acidic solution upon addition to water, or acts as an acceptor of hydroxide ions effectively functioning as a Lewis acid. Acidic oxides will typically have a low pKa and may be inorganic or organic. A commonly encountered acidic oxide, carbon dioxide produces an acidic solution when dissolved.

<span class="mw-page-title-main">Potassium perchlorate</span> Chemical compound

Potassium perchlorate is the inorganic salt with the chemical formula KClO4. Like other perchlorates, this salt is a strong oxidizer although it usually reacts very slowly with organic substances. This, usually obtained as a colorless, crystalline solid, is a common oxidizer used in fireworks, ammunition percussion caps, explosive primers, and is used variously in propellants, flash compositions, stars, and sparklers. It has been used as a solid rocket propellant, although in that application it has mostly been replaced by the higher performance ammonium perchlorate.

<span class="mw-page-title-main">Chloric acid</span> Chemical compound

Chloric acid, HClO3, is an oxoacid of chlorine, and the formal precursor of chlorate salts. It is a strong acid (pKa ≈ −2.7) and an oxidizing agent.

<span class="mw-page-title-main">Hydrogen halide</span> Chemical compound consisting of hydrogen bonded to a halogen element

In chemistry, hydrogen halides are diatomic, inorganic compounds that function as Arrhenius acids. The formula is HX where X is one of the halogens: fluorine, chlorine, bromine, iodine, astatine, or tennessine. All known hydrogen halides are gases at Standard Temperature and Pressure.

<span class="mw-page-title-main">Dichlorine heptoxide</span> Chemical compound

Dichlorine heptoxide is the chemical compound with the formula Cl2O7. This chlorine oxide is the anhydride of perchloric acid. It is produced by the careful distillation of perchloric acid in the presence of the dehydrating agent phosphorus pentoxide:

<span class="mw-page-title-main">Sulfamic acid</span> Chemical compound

Sulfamic acid, also known as amidosulfonic acid, amidosulfuric acid, aminosulfonic acid, sulphamic acid and sulfamidic acid, is a molecular compound with the formula H3NSO3. This colourless, water-soluble compound finds many applications. Sulfamic acid melts at 205 °C before decomposing at higher temperatures to water, sulfur trioxide, sulfur dioxide and nitrogen.

<span class="mw-page-title-main">Sodium perchlorate</span> Chemical compound

Sodium perchlorate is an inorganic compound with the chemical formula NaClO4. It consists of sodium cations Na+ and perchlorate anions ClO−4. It is a white crystalline, hygroscopic solid that is highly soluble in water and ethanol. It is usually encountered as sodium perchlorate monohydrate NaClO4·H2O. The compound is noteworthy as the most water-soluble of the common perchlorate salts.

In chemistry, a strong electrolyte is a solute that completely, or almost completely, ionizes or dissociates in a solution. These ions are good conductors of electric current in the solution.

An oxyacid, oxoacid, or ternary acid is an acid that contains oxygen. Specifically, it is a compound that contains hydrogen, oxygen, and at least one other element, with at least one hydrogen atom bonded to oxygen that can dissociate to produce the H+ cation and the anion of the acid.

<span class="mw-page-title-main">Leveling effect</span> Effect of solvents on properties of acids and bases

Leveling effect or solvent leveling refers to the effect of solvent on the properties of acids and bases. The strength of a strong acid is limited ("leveled") by the basicity of the solvent. Similarly the strength of a strong base is leveled by the acidity of the solvent. When a strong acid is dissolved in water, it reacts with it to form hydronium ion (H3O+). An example of this would be the following reaction, where "HA" is the strong acid:

<span class="mw-page-title-main">Hydrochloric acid</span> Aqueous solution of hydrogen chloride

Hydrochloric acid, also known as muriatic acid or spirits of salt, is an aqueous solution of hydrogen chloride (HCl). It is a colorless solution with a distinctive pungent smell. It is classified as a strong acid. It is a component of the gastric acid in the digestive systems of most animal species, including humans. Hydrochloric acid is an important laboratory reagent and industrial chemical.

<span class="mw-page-title-main">Calcium perchlorate</span> Chemical compound

Calcium perchlorate is classified as a metal perchlorate salt with the molecular formula Ca(ClO4)2. It is an inorganic compound that is a yellow-white crystalline solid in appearance. As a strong oxidizing agent, it reacts with reducing agents when heated to generate heat and products that may be gaseous. Calcium perchlorate has been categorized as having explosive reactivity. Ca(ClO4)2 is a common chemical on the soil of planet Mars, counting for almost 1% of the Martian dust, by weight.

Zirconium perchlorate is a molecular substance containing zirconium and perchlorate groups with formula Zr(ClO4)4. Zr(ClO4)4 is a volatile crystalline product. It can be formed by reacting zirconium tetrachloride with dry perchloric acid at liquid nitrogen temperatures. Zr(ClO4)4 sublimes slowly in a vacuum at 70°C showing that the molecule is covalently bound rather than being ionic. The reaction also forms some zirconyl perchlorate (or zirconium oxyperchlorate) ZrO(ClO4)2 as even apparently pure perchloric acid is in equilibrium with dichlorine heptoxide, hydronium ions and perchlorate ions. This side product can be minimised by adding more dichlorine heptoxide or doing the reaction as cold as possible.

Hydronium perchlorate is an inorganic chemical compound with the chemical formula [H3O]ClO4. It is an unusual salt due to it being a solid and stable hydronium salt. It consists of hydronium cations [H3O]+ and perchlorate anions ClO−4.

<span class="mw-page-title-main">Nitrosyl perchlorate</span> Chemical compound

Nitrosyl perchlorate is the inorganic compound with the formula NO(ClO4). A hygroscopic white solid, it is the salt of the nitrosonium cation with the perchlorate anion. It is an oxidant and strong electrophile, but has fallen out of use with the availability of the closely related salt nitrosonium tetrafluoroborate NO(BF4).

References

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