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Thread: hydrogen ionization

  1. #1 hydrogen ionization 
    Moderator Moderator AlexP's Avatar
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    The hydrogens in a water molecule, which are bonded to one oxygen, will ionize, but the hydrogens in a hydroxyl group, such as in an alcohol, generally do not ionize, even though they too are bonded to a single oxygen. What's the reason for this?


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  3. #2  
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    Well, first we should note that water ionizes only to a very weak extent, since its dissocistion constant , k, is 10^-14.

    Next we note that the proton H+ released from a water molecule is able to associate with another water molecule to form hydronium ion H3O+. An alcohol cannot readily form an analog of hydronium ion.


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  4. #3  
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    I'd say that creating a EtOH2+ cation is is easier than creating an H3O+ cation because due to the induction effect of the ethyl group there is more negative charge on the oxygen. This would mean the oxygen in ethyl is less likely to loose its hydrogen and more likely to gain a proton than the oxygen in water. As a consequence of this, alcoholates are very strong bases as compared to hydroxides.
    As for the gaining-proton part it may be difficult to find examples for, but the same effect causes ethylamine to be more basic compared to amonia. The nitrogen in the amine has more negative charge on it which helps it to compensate the loss of electron when forming a bond with the exess proton in EtNH3+ and the same happens with EtOH2+.
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  5. #4  
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    Quote Originally Posted by SteveF
    An alcohol cannot readily form an analog of hydronium ion.
    Weeel, as I googled "EtOHľ+" I got 37 hits and 16 more with "CH3CH2OH2+" which is no much, but hey, it is not too common, though I think it's more stable then H3O+. Anyway it is pretty much real. :wink:
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