What is the pH of fluoroantimonic acid

Even though there are many kinds of corrosive substance in the world, those portrayed in movies and on TV are, inevitably, always acids. This is because acids are obviously sexier: bodies are dissolved in them in Breaking Bad; extraterrestrials use them as blood in the Alien series of films. You simply don’t hear the same thing about bases – Jack Napier didn’t fall into a vat of sodium hydroxide and emerge as Batman’s nemesis, the Joker; it was a green milkshake-like substance known simply as ‘acid’.

Fact or fiction?

This vagueness is typical of acids in fiction, which are mostly unnamed and generic. So, if we are going to tackle the question ‘what is the world’s strongest acid?’, we’ll need to get a bit more specific than they are in the movies.

We’ll also need a way of measuring and comparing the strength of different acids. And for those of you thinking that pH is, of course, the answer – it will only get us part of the way there. While pH does indeed measure how easily an acid becomes negatively charged when it’s in water, it only makes sense down to pH 0 and is not applicable in non-aqueous systems, which is where we need to look for the baddest of the bad acids.

So, let’s dive headfirst into the world of superacids, which are so strong we’ll need a different way of measuring their acidity. The Hammett acidity function ranks acids by measuring how good they are at pushing an electron onto something other than a water molecule. Its inventor, Louis Hammett, took a series of different reference bases – each one incrementally weaker than the last – then looked at each of them to see if a superacid would totally protonate it, partially protonate it or not protonate it at all. The equilibrium constant of the partially protonated base’s reaction is a measure of acidity and something we can use to arrive at a pH.

Just how strong are superacids? And how do we define one anyway? Well, the ‘strong’ conventional acids you’ll find in your average chemistry lab are fairly brutal, but still orders of magnitude away from a superacid’s strength. For instance, hydrochloric acid comes in at about pH 1.6, nitric acid at 1.08 and pure sulfuric acid at a whopping pH -12. That makes sulfuric acid the strongest ‘normal’ acid you’ll find. Anything more powerful is defined as a superacid.

Superacids are made by taking an already strong (usually Lewis) acid and adding an (often Brønsted–Lowry) acid, which frequently contains the super reactive element fluorine. The fluorine binds preferentially with the Lewis acid, leaving behind a positively charged proton donor that acts as an exceptionally powerful acid.

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It’s a kind of magic

Perhaps the most famous superacid mixture is magic acid (which does sound like it’s from a movie). Invented by the grandaddy of superacid chemistry, George Olah, this comprises a 1:1 mixture of fluorosulfuric acid and antimony pentafluoride. Sounds evil, doesn’t it?

Indeed, once fluorosulfuric acid has given up one of its fluoride ions to the antimony pentafluoride, the resulting HSO3F·SbF5 system has a Hammett acidity (pH equivalent) of -23. That’s 100 billion times more powerful than pure sulfuric acid.

The strongest of them all

Magic acid has found lots of industrial uses, from creating the carbocations that are essential in fuel production, to the removal of NOx from atmospheric smog. But is it the world’s strongest acid?

No. That title falls to fluoroantimonic acid – a superacid mixture of antimony pentafluoride and hydrofluoric acid. You see, HF loves the idea of donating a fluorine to SbF5, and the resulting SbF6- anion is relatively stable. This all results in what is sometimes (wrongly) called a naked proton (it’s actually ‘solvated’ by a number of other HF molecules to form a fluoronium ion). This super acidic system is the strongest ever measured, with a Hammett acidity function of -28. That’s 100,000 times stronger than magic acid.

Put a lid on it?

This leaves us with only one question: what on earth do you keep it in? Here’s a substance so corrosive it will eat through any container, even one made of glass. The answer is poly(tetrafluoroethylene) (PTFE), or Teflon, thanks to its many C–F bonds – famously described as the toughest bond in organic chemistry. Just the thing to contain the strongest acid in the world.

It’s not Hollywood, but there’s a TikTok to go with this story too. 

Dramatic depictions of acid dissolving bodies are widespread in cinema, but the true identities of the caustic fluids are usually left rather vague, begging the question: are they real? There are certainly acids that can dissolve flesh (watch some make quick work of a chicken leg here), but beyond normal acids, exists an elite group of burny-bad-time liquid: the superacids.

Superacids – like fluoroantimonic acid, the strongest acid in the world – are acids that are stronger than 100 percent sulfuric acid. They’re usually made by combining two strong acids, one of which contains the hyper reactive element fluorine, resulting in an exceedingly acidic compound that just loves to give away protons.

What is fluoroantimonic acid?

Fluoroantimonic acid, The Boss of superacids, is a blend of hydrogen fluoride (HF) and antimony pentafluoride.

The superacid known as “magic acid” (made of fluorosulfuric acid and antimony pentafluoride) is 100 billion times the strength of 100 percent sulfuric acid, reports The Royal Society of Chemistry, very much earning the title of “superacid”.

How strong is fluoroantimonic acid? Well, it’s 100,000 times stronger than magic acid, or 10 quadrillion times stronger than pure sulfuric acid. In case keeping on top of all those zeroes is proving difficult, perhaps this video of some chicken being doused in fluoroantimonic acid will help to put all the stats into context.

Is fluoroantimonic acid capable of dissolving anything?

Interestingly, acid strength (which is defined by an acid’s ability to donate protons to other molecules) isn’t always a clear cut measure of corrosiveness. Magic acid was so named after a candle was dipped into it which quickly dissolved, something that was thought to be impossible because candle wax’s hydrocarbons are such stable compounds.

Fluoroantimonic acid, on the other hand, which can transfer protons to methane, does little damage to a birthday candle as seen in this video from Chemical Force. However, with a Hammett acidity function of -28 it’s still pretty intimidatingly corrosive, even able to eat through glass, which is why it has to be stored in the synthetic fluoropolymer Polytetrafluoroethylene (PTFE), also known as Teflon.

While it might not look like much, Teflon contains some of the toughest bonds in organic chemistry (C-F bonds) making it a worthy keeper of fluoroantimonic acid. If that bath tub scene in Breaking Bad taught us anything, it's that things can get very messy when you don't respect an acid's storage suggestion.

What is fluoroantimonic acid used for?

The extreme nature of fluoroantimonic acid makes it a valuable tool in chemical engineering and organic chemistry. Its penchant for giving out protons like Oprah enables it to remove compounds bound to tricky solvents, reports ThoughtCo., such as methane from neopentane.

While TikTok loves cooking up a scandal, from making chlorine gas in a toilet to doing dangerous things with avocados, fluoroantimonic acid is something you absolutely want to steer clear of.

[H/T: The Royal Society of Chemistry]

If you've paid attention in chemistry class, you know acids can have pretty nasty effects on living things. Especially on things like teeth which lead people to purchase supplements like Dentitox Pro. In particular, the lower the pH level, the more acidic, and the more corrosive the substance. But what are the strongest acids in the world? For reference, the acid in your stomach has a pH of about 1.3 to 1.5 (a pH of 7 is considered neutral). But other acids can be tens to thousands of times more acidic than this. Sulfuric acid, for example, is about 10 times more acidic than gastric acid. In 2004, chemists created a superacid, known as carborane acid, and this stuff is at least a million times more acid than concentrated sulfuric acid. The honor of the strongest acid goes to fluoroantimonic acid, which is 100,000 billion billion billion times more acid than gastric acid (pH of -31.3.). This substance is so strong it will eat through skin, bones, and pretty much any container used to store it.

Watch the video to learn how scientists are trying to harness the power of these superacids to combat smog and to make better gasoline and plastics. And if you're looking to push your purchases even further from pollutants, consider switching to leaf leather wallets, handbags, and other sustainable products.

Source: tampabay.com