Chloric acid

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Chloric acid
IUPAC name
Chloric acid
Other names
Chloric(V) acid
Hydrogen trioxochlorate(V)
Molar mass 84.45914 g/mol
Appearance Colorless unstable liquid
Density 1 g/mL, solution (approximate)
>40 g/100 ml (20 °C)
Solubility Soluble in methanol
Acidity (pKa) -1
Safety data sheet Sigma-Aldrich (35% aq. sol.)
Related compounds
Related compounds
Hydrochloric acid
Hypochlorous acid
Chlorous acid
Perchloric acid
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Chloric acid is an unstable, strong, oxidizing acid that can exist in aqueous solutions up to 40%. It is one of the oxoacids of chlorine. Its formula is HClO3.



Chloric acid is a strong oxidizer. Concentrated solutions can light organic materials on fire. It is also a strong acid. It reacts with bases to form chlorate salts.

MOH + HClO3 → MClO3 + H2O

The reaction between chloric acid and metals can take one of the two possible courses. With active metals (sodium to aluminum), little or no reduction of the acid occurs, and the metal reacts with evolution of hydrogen. With less active metals (iron to copper), chloric acid acts like an oxidizing acid and dissolves the metal without evolving any gas, producing chlorates, chlorides and possibly oxides.[1]

Thus, according to Hendrixson, the following metals react with chloric acid as following:

  • Aluminium - Reaction, chloric acid gets reduced
  • Antimony - No significant reaction
  • Bismuth - Slow reaction, oxidizes, small amount dissolves
  • Cadmium - Reaction, complete dissolution, no gases released
  • Copper - Reaction, complete dissolution, no gases released
  • Iron - Reaction, on average around 95% of the chloric acid gets reduced, no gases released, atmospheric oxygen has no measurable effects
  • Magnesium - Reaction, 5% of the Mg reduces the chloric acid, chlorate is formed
  • Mercury - No significant reaction
  • Nickel - Reaction, complete dissolution, no gases released
  • Silver - Reaction, chloric acid gets reduced, no gases released, chlorate and chloride are formed
  • Sodium/potassium - Reaction, chloric acid gets reduced, chlorate is formed
  • Tin - Reaction, complete dissolution, no gases released
  • Zinc - Reaction, 14% of the chloric acid gets reduced, chlorate is formed

When one tries to prepare an overconcentrated solution of this acid (over 40% under vacuum, over 30% by normal pressure boiling), it disproportionates to give a variety of products, which always include perchloric acid, and gases such as chlorine and chlorine dioxide are released:

8 HClO3 → 4 HClO4 + 2 H2O + 2 Cl2 + 3 O2
3 HClO3 → HClO4 + H2O + 2 ClO2

Because of this, chloric acid can serve as a precursor chemical to perchloric acid.


Chloric acid solutions are colorless liquids. Their density is similar to that of water. Concentrated chloric acid (over 30%) has a pungent smell, because of its disproportionation and release of chlorine and chlorine dioxide.

Chloric acid is stable in cold aqueous solution up to a concentration of approximately 30%, and solution of up to 40% can be prepared by careful evaporation of excess water under reduced pressure.


The easiest way to prepare this acid is reacting barium chlorate with sulfuric acid. Concentrations should be stoichiometrically calculated to avoid accidentally preparing an overconcentrated solution that will decompose instantly.


  • Make perchloric acid
  • Make various exotic chlorates for your fireworks, i.e. strontium chlorate for red, calcium chlorate for orange, etc.)



Chloric acid is corrosive, similarly to nitric acid of the same concentrations. It is also known to react violently with oxidizable organic materials. The products of its decomposition are toxic gases. Its ability to set flammable materials on fire is comparable to fuming nitric acid.


Solutions up to 30% can be stored in bottles of amber glass, with ample headroom for gases evolving when the acid decomposes. The acid should be kept cool to avoid decomposition. 31-40% solutions are not advised to store.


One should not dispose of chloric acid directly into the environment. A reducing agent such as sodium or potassium metabisulfite can be used to neutralize it.


  1. Reaction of Chloric Acid with Metals

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