Can you make pure water acidic by adding free protons to it?

[Warp]

Reading a bit about pH and what makes a substance "acidic" or "alkaline", apparently it has something to do with, essentially the ability of the substance to "donate" or "take" extra protons, or something like that.

I was more particularly interested in why pure water (at 25°C) is neutral, ie. has a pH of 7, ie. it's neither acidic nor alkaline, and it has something to do with the number of H+ ions and OH- ions being balanced (assuming there are any), and the involved physics causes naturally the water to keep that balance, which keeps the pH at 7 and the water electrically neutral.

That got me thinking: An H+ ion is just the same thing as a free proton. So what happens if we bombarded pure water with free protons? Would it become acidic?

Apparently the answer is a bit complicated and quite interesting. Free protons are highly reactive and don't stay as free protons for very long. In water, they react with water molecules to either form so-called "protonated water clusters" or hydronium molecules (H3O+). Doesn't really matter where the extra protons are, the pH is (for all intents and purposes) calculated by how many of them there are per unit of volume.

Normally water would be made acidic like this by compensating those extra protons (in protonated clusters or hydronium molecules) with some other substance that has molecules that are negatively charged. However, what I was thinking is: If you are just bombarding pure water with free protons, there are no other substances to balance things out, so would the water become acidic?

Is it so that it cannot happen because if water would accumulate positive charges like this, so the water's net charge would become positive, it becomes unstable and cannot stay that way? Perhaps it will start absorbing free electrons from its environment to compensate, or if those are for some reason unavailable, something will happen to those positively charged molecules?

 

[Borek]

Is it so that it cannot happen because if water would accumulate positive charges like this, so the water's net charge would become positive, it becomes unstable and cannot stay that way? Perhaps it will start absorbing free electrons from its environment to compensate, or if those are for some reason unavailable, something will happen to those positively charged molecules?

Something like that. Try to estimate forces involved between - say - millimole of protons and millimole of electrons separated by 1 meter. Or just watch any video about Kelvin water dropper, while it is not about irradiating solution the general principle - of water becoming charged - is very similar.

An important thing that you omitted is that water by itself dissociates producing H⁺ and OH^-:

H₂O ↔ H⁺ + OH^-

Because of stoichiometry of that reaction amounts of both ions produced is identical in pure water, that's what we call "neutral" - there is no excess neither of "acid" (H⁺) nor "base" (OH^-). It happens concentrations of both in pure water is almost precisely 10^-7 M, hence pH of 7 (and pOH of 7 as well).

 

[Mayhem]

Rule no. 1 chemistry: There are no unbound protons.

Rule no. 2 of chemistry: THERE ARE NO UNBOUND PROTONS

Rule no. 3 of chemistry: Charges are always balanced by an oppositely charged species.

The phenomenon you are describing would not be described by conventional chemistry. You would probably be in the lane of nuclear chemistry at best.

 

[256bits]

That got me thinking: An H+ ion is just the same thing as a free proton. So what happens if we bombarded pure water with free protons? Would it become acidic?

Sure.
Just add some HCl to the water, and you have your water being bombarded by free protons, as the HCl completely dissociates in water into H+ and Cl- ions. The presence of the Cl- ions does not contribute to the acidity of the mixture, but ensures that neutrality complications are avoided.

 

[Warp]

Sure.
Just add some HCl to the water, and you have your water being bombarded by free protons, as the HCl completely dissociates in water into H+ and Cl- ions. The presence of the Cl- ions does not contribute to the acidity of the mixture, but ensures that neutrality complications are avoided.

I understand that, but my question was what would happen if you bombard the pure water with free protons. Not HCl, but just protons.

And yes, I understand that the protons will not remain free when they hit the water, and will quickly form protonated water clusters or hydronium molecules. But the thing is, there will still be extra protons in the water with nothing to compensate, making the water not just acidic but also positively charged.

So I was wondering what happens in that situation. And I assume two possible outcomes:

1. The water absorbs free electrons from its environment to compensate. But if that's so, what happens to those electrons? Do they just bond with the extra protons to form regular hydrogen atoms?
2. If there are no electrons available in the environment, the water will be positively charged and, as far as I know, it can't remain like that and the water will be unstable, so something has to happen to those positively charged molecules. But what?

 

[256bits]

I understand that,

Did you do this? For a start on your research.

Try to estimate forces involved between - say - millimole of protons and millimole of electrons separated by 1 meter. Or just watch any video about Kelvin water dropper, while it is not about irradiating solution the general principle - of water becoming charged - is very similar.

 

[Borek]

So I was wondering what happens in that situation.

To some extent: your guesses are as good as ours.

First of all: as I already signaled there is no way to add enough protons through irradiation to make observable difference in pH.

Other than that - what happens is not much different from what happens during nuclear fusion, where instead of a single atom in the lattice/solution/mixture you have almost instantly two completely different, separated nuclei surrounded by highly ionized matter. Yes, the difference is that it is still electrically neutral (at least in bulk), but all these ions will grab/steal charges from surrounding atoms. Remember when you shot protons at the solution you left electrons somewhere, these charges will move, travel, produce sparks, whatever. The distance is larger, but the idea is still the same.