[icepat]

Well, negative pH is mathematically impossible, given that pH is the -log of the hydrogen ion concentration. It makes no physical sense to discuss "negative hydrogen ion concentration". If anything, it's mostly a shorthand than an actual phenomenon.

[mikeyouse]

If you go one step further than the simple math formula - pH isn't just describing the concentration of hydrogen ions in a solution but rather that solution's ability to donate/accept H+ ions. So a solution of strong acid which is inhibited to fully dissociate into H+ and it's anion would have a pH much lower than the measured value in the solution. As H+ ions are donated, the acid in solution further dissociates providing more H+ ions, so clearly the solution is more acidic than originally measured.

This is how mine water and volcanic hot springs end up with negative pH; https://core.ac.uk/download/pdf/17247528.pdf

[tmearnest]

Check this out https://chemistry.stackexchange.com/questions/5737/is-a-nega...