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Brønsted Lowry definition of an acid says that an acid gives away protons.

What I don't understand is what makes dissolved protons grant the property of acidity? Like, why would dissolved protons eat up materials?

My question applies to bases too, I suppose. And I guess you could include Lewis-acids and bases in your argumentation...

It's a question that has been bothering me for long. By the way I am not chemist(nor do I study chemistry).

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    $\begingroup$ that's due to hydration energy $\endgroup$ – DSinghvi Oct 7 '14 at 14:05
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    $\begingroup$ Does this answer help at all? $\endgroup$ – Nicolau Saker Neto Oct 8 '14 at 1:57
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Whether something is a Brønsted acid is defined by its pH.

$$pH = -log_{10}[H^+]$$

In other words, the better a substance is at releasing protons, the higher the concentration of protons [H+], and correspondingly the lower its pH.

Whereas for Lewis acid, it is the ability for it to strip electrons from anything it attacks (electrophilicity). There is no direct measurement for the strength of Lewis acidity, as many factors have to be taken into consideration, such as enthalpy change, steric factors. In fact, many substances can act as Lewis acids can also act as Lewis bases, such as water, ammonia, and even some alkanes.

Ultimately, what makes acids and bases so corrosive is its ability act as an oxidant or reductant.

Oxidation: Lose electrons/Gain hydrogen.

Reduction: Gain electrons/Lose hydrogen.

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While it is true that oxidizing strong acids like nitric and sulfuric are more corrosive than a non-oxidizing strong acid like hydrochloric, the latter still is able to dissolve materials (e.g, metals, minerals, proteins) and cause burns to the skin. A strong acid like HCl can (in the case of human skin or other biological materials) catalyze the hydrolysis of proteins, fats, and carbohydrates down to their water-soluble components. This is what happens in your stomach, where there is an abundance of hydrochloric acid, as well as enzymes to speed up the process.

The most widely accepted measure of how strong an acid is, its its acid dissociation constant, not the pH of a solution of it.

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