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.