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HClO4, a chlorine oxoacid is commonly known as Perchloric Acid. This mineral acid is either produced by reaction of alkali perchlorates with hydrochloric acid or direct electrolytic oxidation of 0.5 N hydrochloric acid. Though this acid is used to separate potassium from sodium, it is mainly used to prepare ammonium perchlorate, an important rocket fuel component. In addition, perchloric acid is used in many laboratory tests and industrial processes. Though it has vast uses, it should be handled with care as it is dangerously corrosive and readily forms potentially explosive mixtures.
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What is Perchloric Acid?
Perchloric Acid or hydroxidotrioxidochlorine or Hyperchloric acid (HClO4) is a mineral acid produced either by the chemical reaction of high aqueous solubility of sodium perchlorate (NaClO4) and hydrochloric acid (HCl) or by treating barium perchlorate (Ba (ClO4)2) with the sulphuric acid (H2SO4) precipitating perchloric acid. This is a colourless compound, stronger acid than sulfuric acid, nitric acid and hydrochloric acid, unstable oily liquid at room temperature and mainly used to produce ammonium perchlorate, an important rocket fuel component.
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Properties of Perchloric Acid
The properties of perchloric acid are tabulated below:
| IUPAC Name | Perchloric acid |
| Physical appearance | Clear, colourless, and odourless aqueous solution and corrosive to metals and tissues |
| Chemical Formula | HClO4 |
| Density of Perchloric acid | 1.768 g/cm3 |
| Molecular weight of HClO4 | 100.46 g/mol |
| Melting point of Perchloric acid | −17 °C |
| Boiling point of Perchloric acid | 203 °C |
| Aqueous pKa | −15.2±2.0 |
Structure of Perchloric Acid
Structure of Perchloric Acid is as follows:
Ways of Production of Perchloric Acid
There are two routes to produce perchloric acid industrially:
- Treatment of high aqueous solution of sodium perchlorate (209 g/100 mL of water at room temperature) with hydrochloric acid produces perchloric acid precipitating solid sodium chloride:
NaClO4 + HCl → NaCl + HClO4
- Treatment of barium perchlorate with sulfuric acid produces perchloric acid precipitating barium sulphate
Ba (ClO4)2 + H2SO4 → BaSO4 + 2HClO3
- The solution of HClO3 is evaporated further to produce perchloric acid.
3HClO3 → HClO4 + Cl2 + 2O2 + H2O
- Mixing of nitric acid (HNO3) with ammonium perchlorate (NH4ClO4) and adding hydrochloric acid to this solution while the mixture is boiling.
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Uses of Perchloric Acid
Following are the Uses of Perchloric Acid:
- It is used as a precursor to the ammonium perchlorate, a vital rocket fuel component.
- It is used as an oxidizer in the separation of sodium and potassium.
- It is used as a critical compound in the space industry.
- It is used in making explosives.
- It is used in systems etching of Liquid Crystal Display (LCD).
- It is used in plating of metals.
- It functions as a reagent for determining the 1H-Benzotriazole.
- It is for electropolishing or etching of chrome, molybdenum.
- Because of its super acidic property, perchloric acid is one of the major components of Bronsted-Lowry.
- It plays major role in material extraction from their ores.
- Because of its unique property, it is used in analytical chemistry.
- It is also used in electronics industry.
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Health Hazards of Perchloric Acid
Following are the Health Hazards of Perchloric Acid:
- Inhalation of vapours of this compound causes burning sensation in the nose, throat, and lungs.
- Prolonged exposure to this compound causes vomiting.
- Ingestion of this compound can cause blistering and burns in the stomach.
- It is highly corrosive towards human skin as well.
- Because of its oxidizing nature, it is highly reactive towards most metals and liberates irritating, corrosive, and toxic gases when heated. Thus, this compound should be handled with adequate safety measures.
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Points to Remember
Following are the important points:
- Perchloric acid is a chlorine oxoacid with formula HClO4
- It is also called Hyperchloric acid or hydroxidotrioxidochlorine
- It is a colourless and odourless aqueous solution.
- It is dangerously corrosive and thus readily forms explosive mixtures.
- It acts as a strong oxidizer when hot but at room temperature it only shows acidic properties.
- Though it is wide usage but mostly used in the space industry for producing ammonium perchlorate, a major component in rocket fuel.
- Commercially this acid is available in a concentration of 70% (by weight) in water.
- There are two major ways of its industrial production.
- It is one of the strongest Bronsted–Lowry acids.
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Sample Questions
Ques: How is perchloric acid prepared in the laboratory?
Ans: Mostly barium perchlorate is treated with sulfuric acid precipitating barium sulphate and leaving behind perchloric acid. Other method includes boiling mixture of nitric acid with ammonium perchlorate and adding hydrochloric acid to the solution which produces nitrous oxide and perchloric acid.
Ques: Why is perchloric acid considered as strongest acid?
Ans: The strong acidic character of perchloric acid is attributed to the perchlorate which is weakly nucleophilic nature along with negligible susceptibility to hydrolysis compared to other acids namely hexafluoro phosphoric acid, fluoroboric acid etc which are highly susceptible to hydrolysis.
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Ques: What is used to remove water present in perchloric acid?
Ans: Acetic anhydride is used to remove water from perchloric acid whereby acetic anhydride reacts with water present in perchloric acid making the resulting mixture practically anhydrous.
Ques: How is standardization of perchloric acid done?
Ans: It is a common practice to deduct the total volume of perchloric acid consumed by 50ml of glacial acetic acid. Thus each 20.42 mg of potassium phthalate is equivalent to 1ml of 0.1N perchloric acid.
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Ques: What is the reaction of perchloric acid with water?
Ans: Perchloric acid is soluble in water and thus dissociates readily to yield perchlorate anion. In fact, the toxicity of perchloric acid is attributed to this perchlorate anion only.
Ques: How is Para periodic acid produced?
Ans: When a suspension of iodine is heated with Perchloric acid, Para periodic acid (H5IO6) is generated.
2HClO4 + l2 + 4H2O → 2H5IO6 + Cl2
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Ques: Describe the structure of perchloric acid?
Ans: Perchloric acid consists of an H+ is attached with one oxygen atom forming a single bond with chlorine while the 3 remaining oxygen atoms are bonded with chlorine forming a coordinate bond.
Ques: Why is perchloric acid hygroscopic in nature?
Ans: Since Perchloric acid forms azeotrope with water which consists of about 72.5% perchloric acid, thus it has hygroscopic nature.
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