17
$\begingroup$

Generally $\ce{H^+}$ ions in water remain in the form of hydronium ions ($\ce{H3O+}$), and not as "free" aqueous protons, as far as I've been taught.

My question: is this always the case, even when considering dynamics at extremely short time scales? By this I am not meaning interconversion with the Zundel ($\ce{H5O2+}$) or other states. I mean to say, does bare $\ce{H+}(\mathrm{aq})$ ever exist on, say, a femtosecond time scale?

| improve this question | |
$\endgroup$
  • $\begingroup$ I think this is one of those things where there probably is a single proton floating around somewhere in a solution, but the formation of this is so unlikely. It means that you need to have just a hydrogen atom somewhere in solution and some other molecule which will take that electron and form a radical, which is certainly not stabilizing. Then, the proton needs to somehow not react with anything for a femtosecond. My bet is that this just doesn't happen... $\endgroup$ – jheindel Feb 25 '16 at 2:26
  • 2
    $\begingroup$ This is probably more of a philosophical question - when is a H bonded to something, and when is it not? That's quite tricky to answer, particularly in the liquid state... $\endgroup$ – Gerhard Feb 25 '16 at 13:24
  • $\begingroup$ Relevant: chemistry.stackexchange.com/questions/32558/… $\endgroup$ – getafix Jan 1 '18 at 19:19
14
$\begingroup$

According to Myths about the proton. The nature of H+ in condensed media Accounts of Chemical Research, vol. 46, pp 2567–2575:

But to put this into perspective, an electron-free proton has an estimated acidity $10^{56}$(!) times greater than 100% H2SO4, the threshold of superacidity.$^2$ Adding a bare proton to a molecule is a real event in the gas phase but only a solvated hydrogen ion can be transferred in condensed phases.

| improve this answer | |
$\endgroup$
6
$\begingroup$

No. The proton is always within some electron density, even when transitioning between the hydronium/water and whatever anion it was bonded with.

| improve this answer | |
$\endgroup$
  • 3
    $\begingroup$ To expand on this answer: Say a proton moves from one water molecule to another. It does not jump off and become a bare proton, even for a moment. Rather the second water molecule begins to form a bond with the proton as the first water molecule begins to loosen, leading to a transition state where the proton is partially bonded to both water molecules. $\endgroup$ – Oscar Lanzi Mar 7 '16 at 0:49

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.