| Oxohalic Acids |
What a fearsome name, oxohalic acid. It just means halogen atoms combined with oxygen and an acidic hydrogen. In fact, the Germans use the same saurstoff, meaning "Stuff that makes things sour" (acidic). Oxygen is good at that for reasons that will become apparent later. (I'm always saying that, aren't I?) | ||||||||||||||||||||||||||||
| Right now, while we're naming names, I need to tell you where these guys fit into the scheme of things. For although H+ is a monopositive cation like Na+, it is radically different from any other cation in the Universe. The difference is easy to explain. Take Na; it's an atom with 11 protons and 11 electrons. Neutral. OK. Now kick one electron off, and you have Na+, but you also still have 10 electrons left to guard the nucleus and not permit any other atom or ion to get to the nucleus. | |||||||||||||||||||||||||||||
| Not so with hydrogen. H had only one electron! So H+ has no electrons left! It is a bare, naked proton, and anything that wants to walk right up to it can. What does the lose of its electronic security blanket mean? | |||||||||||||||||||||||||||||
| Acids Are Special |
It means that things foolish enough to walk up to H+ are subjected to very serious forces. You remember that electrostatic force varies inversely with distance. So if you can make that distance zero, you feel infinite force! It is so strong, in fact, that H+ cannot exist in aqueous solution (water). Instead, the proton sees an electron-rich oxygen end of the neighboring water molecule and bonds to it to create the hydronium ion, (H3O)+. It's usually given as H3O+, but you have to agree that it is the hydrogens that are carrying that positive charge, not the oxygen, as that simpler formula seems to suggest. In other words, the charges on molecular ions are borne by the whole ion not just by whatever atom happens to get written last. | ||||||||||||||||||||||||||||
| H3O+ is tha Soul of Acids, at least in aqueous solutions. And the naked proton's lack of an electronic security blanket means that the proton can really push other charges around. That's what makes acids special: they give you a good handle on bullying electrons. And electrons are Chemistry in the sense that they are the only thing atoms touch about one another. So if you can bully them, you can encourage or discourage reactivity. | |||||||||||||||||||||||||||||
| All of this is to justify why NaClO3 is merely sodium chlorate while HClO3 gets the exalted name of chloric acid. That hydrogen is strongly acidic. In face, the hydrogen in HClO4 is regarded as the strongest acid in the Universe. (Must be what swims inside Ridley's Aliens.) | |||||||||||||||||||||||||||||
| Well, that might explain why it is important to tack on the word "acid," but how does chlorate transmigrate to
chloric? Gotta be an alchemical thing. When you acidify an -ate ion, you get an -ic acid. Likewise, when you
acidify an -ite ion you get an -ous acid. Sounds silly, doesn't it? But with that hint, you ought to be able
to fill out the rest:
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| Disclaimer | OK. I pulled a fast one on you. The stuff blushing pink, HCl(aq), doesn't belong in this discussion because he's not an oxoacid . . . no oxygen. But he is still an acid, and hydrochloric acid is his name. HCl(aq) is also the only one I bothered giving an explicit (aq) designation, because, he's called something different if he is in a vapor, say, rather than dissolved in water. The difference is that in water, HCl completely dissociates into its constituent ions; we'll discover that that is the hallmark of a strong acid. But in a vapor, HCl(g) is the molecule called hydrogen chloride. For that matter, if you solidified the stuff, HCl(s) would still be hydrogen chloride; it's only hydrochloric acid when it dissolves in water. | ||||||||||||||||||||||||||||
| Just to complete this part of the story, not all oxoacids are strong. HClO4 is. And HClO3 almost is. But it falls off down the table for the oxohalic acids. We'll return to this strong vs. weak thing later. | |||||||||||||||||||||||||||||
| THE MOLE NAv ~ 6.02×1023 |
is so important that he has his own holiday: Mole Day which begins at 6:02 am on October 25th (that's 10/25, of course). You think I'm joking, but I'm not. For us, however, the mole is just a number like "a dozen" only a bit more impressive. The significance of this Systeme Internationale standard count, of course, is that it scales atomic mass units, u, up to grams! | ||||||||||||||||||||||||||||
| 1 gm = 1 u × NAv so 1 u = 1 g / 6.0221367×1023 = 1.6605620×10-24 g | |||||||||||||||||||||||||||||
| I didn't even waste space on your Periodic Table with u, since all you have to do is invert NAv to get it. | |||||||||||||||||||||||||||||
More later . . .