The World's Strongest Acid: A Deep Dive Into Extreme Acidity

By: Allison Troutner & Austin Henderson  | 
Fluoroantimonic acid
Fluoroantimonic acid is the strongest superacid known to man. Wikimedia/(CC BY-SA 3.0)

Some acids are safe enough that even a homeowner can use them, like muriatic acid. It's designed to be used as a household cleaner, as long as you follow the directions and all safety precautions. Some other acids are simply too caustic and corrosive for anyone to handle.

So what happens when you mix two of those? You get something altogether stronger. For instance, when equal amounts of the acids hydrogen fluoride (HF) and antimony pentafluoride (SbF5) are combined, the results are too remarkable to ignore.


You don't get just any other acid. You end up with the strongest acid, or superacid, known to humankind: fluoroantimonic acid, aka HSbF6.

What Is Flouroantimonic Acid?

Fluoroantimonic acid is a colorless liquid that emits a toxic vapor. Swallowing or inhaling it can be fatal, and skin contact? Think severe burns. It stands tall in the superacid category, a group of strong acids with acidic strength surpassing that of sulfuric acid.

Given its potency, we can't use the regular pH or pKA scales to measure its strength. Here, the Hammett acidity function, denoted as H, steals the spotlight.


Fluoroantimonic acid registers an H of -21, while sulfuric acid's H measures -12. To translate that, fluoroantimonic acid is a staggering 20 × 10¹⁹ times stronger than pure sulfuric acid.

If this were a showdown, it would like Captain Marvel squaring off against a newborn kitten.

Hydrogen Fluoride and Hydrogen Ions

This is the backbone of our champion, fluoroantimonic acid. Hydrogen ions make a substance acidic, and the higher the concentration, the more potent the acid. Hydrogen fluoride, on its own, isn't the strongest acid, but it is a key component of some very strong ones.


Fluoroantimonic Acid's Kryptonite: Teflon

Despite its overwhelming strength, fluoroantimonic acid has an Achilles' heel: It can't erode polytetrafluoroethylene (PTFE), commonly known as Teflon.

Thus, Teflon containers are the chosen vessels to store this potent liquid. Another storing method is within a hydrofluoric acid solution, where our record holder doesn't undergo explosive decomposition.


Beware, though — this acid will dissolve glass, most plastics and every organic compound. It even reacts explosively with water.

It's most definitely not a school science experiment. It demands respect, best left to seasoned chemists and experts in organic chemistry.


Protonation: Fluoroantimonic Acid's Superpower

Fluoroantimonic acid's unique talent is protonation — it donates protons to organic compounds. This alters the compound's properties like mass, solubility and hydrophilicity.

Such a trait is invaluable to chemists, aiding in chemical reactions, etching glass, refining gasoline and even crafting explosives. While it holds the title of the world's strongest acid, some argue hydrofluoric acid is riskier due to its presence in common products, making accidental exposure likelier.


For those brave enough to work with superacids, personal protective equipment, including respirators and protective eyewear, is non-negotiable. It's the modern chemist's armor against a substance that can dissolve flesh and bones in a blink.

Comparing to Other Acids

The chemical realm is vast, and while fluoroantimonic acid has its revered status, there's an array of other fascinating acids that deserve a mention. Let's explore the unique attributes of these acids, diving into their strengths, weaknesses and roles in various processes.

Carborane Acids

These are among the strongest of the strong acids, next only to fluoroantimonic acid. Their unique molecular structure, backed by the American Chemical Society's research, helps them maintain their potency.


What sets them apart is their weak bond with hydrogen ions, making them less corrosive than fluoroantimonic acid.

Magic Acid

It sounds fantastical, but magic acid is very real! It's formed by mixing fluorosulfuric acid (HSO₃F) and antimony pentafluoride (SbF₅). This acid completely dissociates in an aqueous solution, releasing a high concentration of hydrogen ions.

Nitric Acid, Phosphoric Acid and Perchloric Acid

These are examples of strong acids that completely dissociate when dissolved in water. While they may not match the extreme acidity of fluoroantimonic acid, they're essential in industries, ranging from fertilizer production to rocket propellant.

Benzoic Acid and Oxalic Acid

These weak acids don't completely dissociate in water. However, they play crucial roles in our daily lives, from food preservation to cleaning agents.

Hydronium Ion

All acids, when dissolved in water, produce this positively charged ion. It's the real culprit behind the acidic properties of a solution.

This article was updated in conjunction with AI technology, then fact-checked and edited by a HowStuffWorks editor.