Re: Why is CHB11R5X6 a strong acid?

There are several definitions of acidity that are used by chemists. The simplest (and first one formulated) is the Arrhenius (or "Classical") definition which says that an acid has H+ in its formula and dissociates it in water. This is the sort of acid that we think of when we are talking about Hydrochloric or Sulphuric Acid. Readily ionized protons which dissociate completely or almost completely. The proton in solution is the corrosive component as it will react with other species and eat away at metals and such.

However, another definition of acid is the Bronsted-Lowry definition which states:

"An acid is a proton donor, any species that donates an H+ ion." (and "A base is a proton acceptor, any species that accepts an H+ ion.")

So, what is the difference? It is subtle. Arrhenius acids donate their protons to the water molecule. This is how they become dissociated in aqueous solution. But Bronsted-Lowry acids will donate to other acceptors than water. They will donate a proton to any number of compounds. And the stronger they are, the more capable they are at donating a proton.

In this case, the authors demonstrated that their carborane acid was capable of donating a proton to benzene (giving C6H7+) which is something that oxyacids can not do. Indeed, it is apparently stronger than any other superacid.

However, is it corrosive? No. It donates the proton to other species but is not very good at donating the proton to water in the same way that an Arrhenius acid does. Hence, it is an acid but not like "HCl" or "H2SO4".

Hope this helps. And I hope that you don't really find stronger acids "scary to imagine". Acids are certainly not the stuff that we see in movies bubbling away people's skin or destroying objects. The movies and television shows tend to exaggerate!