hyperion210
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self-ionization of water
Can someone describe to me the self-ionization of water? I'm just trying to get a better understanding of how it happens and what it implies. I know
the answer may be rather simple but my text does not explain it at all and I'm curious.
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psychokinetic
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Water, at standard environment settings, is ionised into equal amounts of hydroxide and hydronium (in equilib. with H2O).
The attachment and detachment of hydrogen is done via hydrogen bonding (easy, what with all the lone pairs hanging out on the oxygen)
What did you want to know about it?  (I'm sorry, I don't want to say lots and
have it go over your head OR be too simple and make you feel like I assume you're an idiot. I can't tell what your knowledge is.)
EDIT: I didn't say that very well, and I still haven't.
[Edited on 1-6-2010 by psychokinetic]
“If Edison had a needle to find in a haystack, he would proceed at once with the diligence of the bee to examine straw after straw until he found
the object of his search.
I was a sorry witness of such doings, knowing that a little theory and calculation would have saved him ninety per cent of his labor.”
-Tesla
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12AX7
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There's an old rule in chemistry, indeed in physics in general: if it can happen, it will. You just have to provide enough energy to make it proceed
at a noticable rate. In the case of water, ordinarily it would "like" to sit around as a whole molecule. (And let me be specific here: when a
physicist or chemist uses the phrase "likes to", they mean "attains a lower energy state", since after all, molecules have no sentient will of their
own.) It is possible for a hydrogen to split off, leaving a charged OH- core behind, while sticking to another water, forming H3O+. (And both of
these have more molecules sticking to them because of the charge, but for simplicity we'll ignore them.) This causes charge seperation, which is a
fairly bizarre thing to happen at random -- it takes a lot of energy to pull charges out of nowhere! Since there's only so much energy available at
room temperature, this only occurs rarely, about one part in 10^-14.
More dramatic reactions, like the outright dissociation of water, occur at much higher temperatures. It takes an awful lot of energy to make H2 and
O2 from H2O, and this occurs spontaneously at near-plasma temperatures (>3000K!).
Tim
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hyperion210
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Thank you Tim that was just the sort of overview I was looking for! All I was given by my teacher was the ion-product constant and basic math
applications for it and she's not very helpful when it comes to asking questions so thanks again for taking the time to answer a very simple question.
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Magpie
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The ion product is 10^-14 so that means 10^-7 moles/liter of water have dissociated. This would be 10^-7mole/55moles, or about 2 molecules per
billion molecules.
The single most important condition for a successful synthesis is good mixing - Nicodem
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