Perchloric acid

Perchloric acid is a chemical compound made of hydrogen, oxygen, and chlorine. It is a very strong acid and oxidizer, and very corrosive. It is a colorless liquid.

Salts of perchloric acid are called perchlorates. Perchloric acid is mostly used to make ammonium perchlorate, which is used in rockets.

Properties

Perchloric acid is a very strong Brønsted acid, meaning it can give up a hydrogen ion to other chemicals (Brønsted bases) very easily. The word "superacid" was first used by scientists researching perchloric acid.^[1]

Perchloric acid and its conjugate base perchlorate are also very strong oxidizers. Perchloric acid is a common ingredient in solid rocket fuel, usually as ammonium perchlorate.

Preparation

Perchloric acid is normally made by the reaction of hydrochloric acid and perchlorate salts, or by electrolysis of hydrochloric acid or a solution of chlorine gas in water.^[1]

Making perchloric acid from perchlorate and hydrochloric acid can seem unintuitive. According to the Brønsted–Lowry acid–base theory, an acid and base will react if they can make a weaker acid and base. Perchloric acid is stronger than hydrochloric acid, and chloride is stronger than perchlorate, so the chemical equilibrium

HCl + ClO−4 ⇌ HClO₄ + Cl⁻

should mostly stay on the left side (the reactants). The reaction works because sodium perchlorate dissolves much more easily in water than sodium chloride, so a precipitate will form. This removes chloride from the solution, stopping the reverse reaction and leaving the perchloric acid on its own.^[2] This is an example of Le Chatelier's principle.

Related pages

Sources

1 2 George A. Olah, G. K. Surya Prakash, Arpad Molnar, and Jean Sommer (2009). "2.1.1.1 Perchloric Acid". Superacid Chemistry (2nd ed.). John Wiley & Sons, Inc. p. 35. ISBN 978-0-470-42154-3.{{cite book}}: CS1 maint: multiple names: authors list (link)
↑ Mathers, Frank C. (1910). "THE PREPARATION OF PERCHLORIC ACID FROM SODIUM PERCHLORATE.¹". Journal of the American Chemical Society. 32 (1): 66–71. Bibcode:1910JAChS..32...66M. doi:10.1021/ja01919a004.

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[olahSAC-1] 1 2 George A. Olah, G. K. Surya Prakash, Arpad Molnar, and Jean Sommer (2009). "2.1.1.1 Perchloric Acid". Superacid Chemistry (2nd ed.). John Wiley & Sons, Inc. p. 35. ISBN 978-0-470-42154-3.{{cite book}}: CS1 maint: multiple names: authors list (link)

[2] Mathers, Frank C. (1910). "THE PREPARATION OF PERCHLORIC ACID FROM SODIUM PERCHLORATE.¹". Journal of the American Chemical Society. 32 (1): 66–71. Bibcode:1910JAChS..32...66M. doi:10.1021/ja01919a004.

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