Re: What Is the Strongest Acid?

Hi Karen,

Thanks for the question. I think the disparity here is that your chemistry book and your boyfriend are using the word "strong" in different senses.

In chemistry, we can define an acid in several ways. One way is to say that it is a substance that donates protons (hydrogen ions). So when say hydrochloric acid is dissolved in water, it dissociates into protons and chloride ions.

Chemically, we use the word strong to define the degree to which the acid dissociates, or liberates protons. So in this sense your textbook is correct; perchloric acid dissociates the most completely, then hydrochloric, sulfuric, nitric and hydrofluoric acids. This is because of the bond strengths in each acid (perchloric has the weakest, hydrofluoric the strongest).

However, in every day language, strong is used to mean corrosive. In this sense your boyfriend is right, hydrofluoric is the most corrosive of those acids, able to eat through many types of metal container. But chemically- speaking, it is not a strong acid!

Neil Saunders