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What Is the World's Strongest Superacid?

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This is the chemical structure of fluoroantimonic acid, the strongest superacid.

This is the two-dimensional chemical structure of fluoroantimonic acid, the strongest superacid.

YOSF0113, public domain
Question: What Is the World's Strongest Superacid?
You may be thinking the acid in the Alien blood in the popular movie is pretty far-fetched, yet there is an acid that is even more corrosive! Learn about the word's strongest superacid.
Answer: The world's strongest superacid is fluoroantimonic acid, HSbF6. It is formed by mixing hydrogen fluoride (HF) and antimony pentafluoride (SbF5). Various mixtures produce the superacid, but mixing equal ratios of the two acids produces the strongest superacid known to man.

Properties of Fluoroantimonic Acid Superacid

  • Rapidly and explosively decomposes upon contact with water.

  • Evolves highly toxic vapors.

  • Fluoroantimonic acid is 2×1019 (20 quintillion) times stronger than 100% sulfuric acid. Fluoroantimonic acid has a H0 (Hammett acidity function) value of -31.3.

  • Dissolves glass and many other materials and protonates nearly all organic compounds (such as everything in your body). This acid is stores in PTFE (polytetrafluoroethylene) containers.

What Is It Used For?

If it's so toxic and dangerous, why would anyone want to have fluoroantimonic acid? The answer lies in its extreme properties. Fluoroantimonic acid is used in chemical engineering and organic chemistry to protonate organic compounds, regardless of their solvent. For example, the acid can be used to remove H2 from isobutane and methane from neopentane.

Reaction Between Hydrofluoric Acid and Antimony Pentafluoride

The reaction between hydrogen fluoride and antimony pentrafluoride that forms fluoroantimonic acid is exothermic.

HF + SbF5 → H+ SbF6-

The hydrogen ion (proton) attaches to the fluorine via a very weak dipolar bond. The weak bond accounts for the extreme acidity of fluoroantimonic acid, allowing the proton to jump between anion clusters.

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