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Fluoroantimonic Acid: The Strongest Acid in the World

Eric is a bookwormy and logophilic science and technology teacher. He often writes about scientific thought, theories and, research.

Molecular model of fluoroantimonic acid

Molecular model of fluoroantimonic acid

What Is a Superacid?

Superacids are any acid in which the acidity is stronger than pure sulfuric acid. One of the superacids is fluoroantimonic acid. Fluoroantimonic acid is known for its extraordinary corrosiveness. It is remarkably strong and can corrode almost all things.

As a matter of fact, it is generally considered as the strongest acid known to man. How strong is this superacid? Is it dangerous? If it is dangerous, why do people still produce this material? This article discusses many facts about this substance, including its properties, its danger, and its uses.

Properties of Fluoroantimonic Acid

Fluoroantimonic acid does not stand as a single chemical. It is a mixture of two substances — hydrogen fluoride (HF) and antimony pentafluoride (SbF5). Hydrogen fluoride is a toxic, colorless gas or fuming liquid that is typically used as a refrigerant that helps refrigerators and air conditioners cool due to its ability to carry heat. Antimony pentafluoride, on the other hand, is a toxic, corrosive, colorless oily liquid. It is used to produce fluorine gas. Mixing antimony pentafluoride and hydrogen fluoride at a 1:1 ratio forms fluoroantimonic acid.

Fluoroantimonic acid is a colorless liquid at room temperature, but when heated at 40°C, it decomposes because the hydrogen fluoride evaporates and separates from antimony pentafluoride. Fluoroantimonic acid has a molecular formula of SbHF6. It has a density of 2.885 g/cm3. It is a very reactive substance and can react to almost everything. It is a moisture-sensitive substance and reacts violently with water. It has an H0 value of - 31.3, the highest level of acidity ever recorded.

Chemical structure of fluoroantimonic acid

Chemical structure of fluoroantimonic acid

Acidity

The acidity of a substance can be measured using its pH or the H0 value. Fluoroantimonic acid has an H0 -31.3. H0 or Hammet acidity function is the same as the pH or power of hydrogen, but the difference is the pH value runs from 0 - 14 while the H0 value runs below zero.

The neutral pH is 7. A pH that is greater than 7 is more alkaline or basic, while a pH lower than 7 is acidic. A pH that is lower than zero is H0. A substance that has an H0 value is either a very concentrated strong acid or a superacid.

To give you an idea of how strong H0 -31.3 is, let's compare it to the pH or H0 of the other materials such as things on the pH chart below.

fluoroantimonic-acid-the-strongest-acid-in-the-world

The pH or H0 is a logarithm scale. It can calculate using the expression: pH = - log [H3O+]. The expression seems very difficult to calculate but there is a better idea to understand it. For a simple explanation, it only means that for each one-digit change in pH, the acidity changes by 10 times. For example, the pH value of pure rain is around 6, which means, pure rain is around 10 times more acidic if compared to freshly distilled water which has neutral pH of 7.

The pH of coffee is 5, thus, coffee's acidity is 100 times more powerful compared to pure water. The tomato's pH is 4, meaning, the acidity of the fruit is 1000 times stronger compared to water. The vinegar has a pH value of 5, which means it is 10,000 more acidic compared to water. Lemon juice has a pH value of 2, therefore, it is 100,000 more acidic than water.

Muriatic acid's or hydrochloric acid's pH is 1, so muriatic acid is 1,000,000 times more acidic than water. The 100 % pure sulfuric acid has an H0 of -12, which means, it is 1X1019 times more acidic compared to water. Fluoroantimonic acid has an H0 of -31.3, so its acidity is 3X1038 times stronger than to freshly distilled water. If you compare the acidity of muriatic acid and pure sulfuric acid to fluoroantimonic acid, fluoroantimonic acid is over 2 undecillions (2,000,000,000,000,000,000,000,000,000,000,000) times more acidic compared to muriatic acid and over 20 quintillions (20,000,000,000,000,000,000) times more potent than pure sulfuric acid.

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Fluoroantimonic acid is a super strong and super corrosive superacid. It can corrode almost everything even rocks, glass, ceramics, and many kinds of plastics.

Storing

Fluoroantimonic acid can corrode glass and ordinary plastics at home, so a container that is made of glass or ordinary plastic is not used to store this superacid. It is stored in a container that is made of or coated with polytetrafluoroethylene (PTFE). Polytetrafluoroethylene is a waxy superplastic known for its high strength and toughness. It has a high melting point and is resistant to friction and attacks of almost all chemicals. You are familiar with this superplastic because it is also the material used as a coating in the inner part of nonstick cookware.

Polytetrafluoroethylene does not dissolve in fluoroantimonic acid because PTFE is a stable, and non-reactive chemical so it is unlikely to react and bond with other chemicals like the SbHF6. PTFE's electrons are held so tightly that they are not available to accept the protons of the superacid. Moreover, PTFE is a nonpolar molecule while SbFH6 is a polar molecule. In a rule of solubility, polar molecules can only dissolve polar molecules, while non-polar molecules can only dissolve non-polar molecules, therefore, SbFH6 is unlikely to dissolve PTFE.

Polytetrafluoroethylene is the material used to store fluoroantimonic acid. It is the same material used to coat the inner part of nonstick cookware.

Polytetrafluoroethylene is the material used to store fluoroantimonic acid. It is the same material used to coat the inner part of nonstick cookware.

Dangers of the Substance

As mentioned above, fluoroantimonic acid is very corrosive and can dissolve almost everything. It is a very dangerous material that's why it is exclusively used and produced in laboratories and can only be handled by chemists or experts in chemicals.

Fluoroantimonic acid is 20 quintillion times stronger than pure sulfuric acid. So, you have now an idea of how dangerous this acid is. Just inhaling the fumes of this substance can cause breathing difficulty and can injure respiratory tracts. In severe cases, it can cause pulmonary edema, circulatory failure, and possibly death. When it comes into contact with the skin, it can cause severe skin burns and painful blisters. It can also corrode flesh and bones. And it doesn't end there. The acid explodes while corroding body tissues because it reacts with the moisture in the body. Prolonged and repetitive exposure to fluoroantimonic acid can cause damage to the cardiovascular and respiratory systems and death.

Moreover, if it contacts combustible or flammable materials, it can ignite a fire and causes blazing. It can also pose a potential threat to the environment if improperly discarded.

Applications

The most common use of fluoroantimonic acid is to protonate organic compounds. To protonate means to transfer a proton to other atoms, molecules, or ions. Protonation can change the chemical properties of a substance including the substance's charge, mass, solubility, and hydrophilicity.

Fluoroantimonic acid is also used to etch glass, enhance the quality of gasoline, synthesize plastics, and manufacture explosives.

Some Experiments and More Facts About Fluoroantimonic Acid

Sources of Information:

This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.

© 2021 Eric Caunca

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