Perchloric Acid - HClO₄

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What is Perchloric Acid?

HClO4 is a chlorine oxoacid with the chemical name Perchloric acid. It is also called hydroxidotrioxidochlorine or Hyperchloric acid (HClO4). Ranging from 50 -72%, acid is a clear, colorless, and odorless aqueous solution. It is corrosive to metals and tissues. When closed containers are exposed to heat for a long duration can violently rupture.

Properties of Perchloric Acid – HClO₄

Let us look at the properties of perchloric acid tabulated below.


Perchloric acid

Chemical Formula


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

Perchloric Acid Structure – HClO₄

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Production of Perchloric Acid

Perchloric acid can be produced at an industrial level using two methods. The traditional method makes full use of high aqueous solubility of sodium perchlorate (NaClO4). Considering this solution with hydrochloric acid (HCl) forms perchloric acid by precipitating the solid sodium chloride. The reaction can be as follows:

NaClO4 + HCl → NaCl + HClO4

The second method is much direct and keeps away from salts, and needs the solution of anodic oxidation chlorine at a platinum electrode.

It can also be prepared in chemical laboratories by treating barium perchlorate (Ba(ClO4)2) with the sulphuric acid (H2SOv) that precipitates barium sulfate (BaSO4) and then leaves perchloric acid. In an alternate way, it can be prepared by mixing nitric acid (HNO3) with ammonium perchlorate (NH4ClO4) and adding hydrochloric acid while it is boiling.

Uses of Perchloric Acid

  • Perchloric acid's main application is its usage as a precursor to the ammonium perchlorate, which is an inorganic compound and a vital component of rocket fuel. 

  • Thus, perchloric acid is considered to be a more critical chemical compound in the space industry.

  • The same compound can also be used in the Liquid Crystal Display (LCD) systems etching.

  • Thus, perchloric acid has started using widely in the electronics industry too.

  • This compound can also be used in analytical chemistry owing to its unique properties.

  • Perchloric acid also holds many essential applications in the material extraction from their ores.

  • Furthermore, this specific compound is also used in chrome etching.

  • Because it acts as a superacid, the perchloric acid has considered being one of the strongest acids of Bronsted-Lowry.

As an Acid

Perchloric acid, which is a superacid, is one of the strongest Bronsted Lowry acids. Its pKa falls below −9, which is evidenced by the fact that its monohydrate has discrete hydronium ions and is isolated as a crystalline and stable solid, which is formulated as [H3O+][ClO–4]. The recent estimate of its aqueous pKa is given as −15.2±2.0. It also provides strong acidity with minimal interference since the perchlorate is weakly nucleophilic (describing the high acidity of HClO4). 

Other noncoordinating anion acids, such as hexafluorophosphoric acid and fluoroboric acid, are susceptible to hydrolysis, but the perchloric acid is not. Apart from the hazards associated with its salt explosiveness, the acid is often preferred in specific syntheses. For the same reasons, it is also a useful eluent in ion-exchange chromatography.

It can also be used for etching or electropolishing molybdenum, aluminium, and several other metals.

Health Hazards

Inhaling vapors of this specific compound causes a burning sensation in the nose and throat, irritating the lung, including coughing. Prolonged exposure to this compound causes vomiting. Ingesting this can cause blistering and stomach burns. When this compound is heated, it liberates irritating, corrosive, and toxic gases.

Perchloric acid is considered an extremely powerful oxidant. Owing to this compound's strongly oxidizing properties, it exhibits very high reactivities towards most of the metals. Moreover, this compound is also highly reactive towards the organic matter. This compound is corrosive towards the human skin. Thus, adequate safety measures should be taken while handling this compound.

Why is Perchloric Acid Considered to Be the Strongest Acid?

HClO4 is perchloric acid. In this, H+ is attached with one oxygen atom, which forms a single bond with chlorine, and the remaining 3 oxygen atoms are bonded with chlorine with a coordinate bond. A compound is referred to be acid if it furnishes proton in the aqueous solution, whereas it is said to be a strong acid if its conjugate base is stable. So, in that case, the perchlorate ion's stability is because of the negative charge conjugation developed on the oxygen atom, overall the 3 other oxygen atoms.

Laboratory Preparations of Perchloric Acid

The treatment of barium perchlorate with the sulfuric acid precipitates barium sulfate by leaving perchloric acid. This acid can also be prepared by mixing the nitric acid including ammonium perchlorate and boiling at the time of adding hydrochloric acid. The reaction produces perchloric acid and nitrous oxide because of a concurrent reaction involving the ammonium ion. It is purified and concentrated significantly by boiling off the remaining hydrochloric and nitric acids.

FAQ (Frequently Asked Questions)

1. Explain the safety of perchloric acid?

Given the perchloric acid's strong oxidizing properties, it is subject to extensive regulations. It is also highly reactive with metals (for example, aluminium) and organic matter (such as wood, plastics). Work conducted with the perchloric acid should be conducted in fume hoods with a wash-down capability to prevent oxidizers accumulation in the ductwork.

2. Give the uses of perchloric acid?

Mainly, perchloric acid can be produced as a precursor to the ammonium perchlorate, used in rocket fuel. The rocketry growth has led to increased production of this acid, where many million kilograms are produced on an annual basis. This acid has also be considered to be one of the most proven materials for liquid crystal displays etching and critical electronics applications as ore extraction as well, and it holds unique properties in analytical chemistry. Besides, it can be considered a useful component in the etching of chrome.

3. Differentiate strong acid vs. weak acid?

A strong acid dissolves in water, totally split in H+ and negative ions. A weak base will be dissolved in water will partially take up an H+ from the water molecules till we hold an equilibrium.

When we put equal amounts of strong acid and weak base together, the reaction continues till one of the compounds is finished.

4. What is perchloric acid?

Perchloric acid can be described as a mineral acid having the chemical formula HClO4. It is generally found as an aqueous solution, and this colorless compound is a stronger acid than nitric and sulfuric acids.