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Name: mwang
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Date: 1999 

How do you distinguish between two acids that are both 100% dissociated?

Interesting question there...the strongest acids are sometimes referred to as "superacids." These have an extremely large proton-donating ability. Usually an acid is considered to be a superacid if it has a proton-donating ability greater than / equal to that of 1nhydrous (100%) sulfuric acid.

Apparently the strongest acid is hydrogen flouride (HF).

Upon reading, it seems that it is actually tough to distinguish between the superacids on the basis of their pH alone. All strong acids are fully ionized in dilute solution, and therefore they all appear to have the same strength, equal to that of the hydronium ion (h3O+), which is the most highly acidic species that can exist in water. So all of these have the same pH on a per-proton basis.

So, to rank superacids, chemists measure how strongly they tend to react with a given base, B;
HA + B --> BH+ + A

This way, even superacids can be ranked relative to one another in terms of their "strength." HF is the strongest in the table I am looking at, followed by HSO3F, H2S2O7, HSO3CF3, HSO3Cl, and H2SO4 (sulfuric acid).

All my data is from the McGraw-Hill Encyclopedia of Sci/Tech.


Revised 2002

A student in my Chemistry class at Ohio State Univ. found the following on your system. It is incorrect. HF is a weak acid (Ka = 6.8 x 10-4) and does NOT completely ionize. As given in most first year chemistry textbooks, the common strong acids that ionize completely in H2O are:

HCl, HBr, HI, HNO3, HClO3, HClO4 and H2SO4 (only the first proton comes off completely, HSO4- is a weak acid with Ka=1.2 x 10-2)

R Zellmer

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