pH of a non aqueous solution

[neeraj]

Hi friends

How could one determine the pH of a non aqueous solution. i.e. solution made in organic solvents

plz suggest

[hermanntrude]

the pH scale is really only applicable to aqueous solutions, since it is the negative logarithm of the concentration of hydronium ions.

 

Now while there will be a few hydroxonium ions in any solution, no matter how dry, unless there is a VERY significant impurity in the non-organic solution, the concentration of hydronium ions will be very very low indeed, which, in an aqueous solution would translate to a high pH (perhaps 13 or 14), which would also mean that the hyoxide ion concentration would be very high, which would mean the solution was basic and probably highly corrosive. This isn't true of our non-aqueous solution, though, since there may be no hydroxide ions at all or, more likely, exactly the same amount as there are hydronium ions, meaning the solution is actually neutral.

 

Remember that in an aqueous solution, pH and pOH are tied together via PKw (PKw is the legative logarithm of the equilibrium constant for the auto-ionization of water ([ce]2H2O <=> H3O+ + OH- [/ce]). pH + pOH = pKw = 14), but this doesnt work in a non-aqueous solution because any water that is present is an impurity and therefore part of a mixture rather than a pure aqueous solution.