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Calculate pH using Ionic Strength

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BHAVESH:
Hi,
Is there any way to calculate pH of water based on Ionic Strength?

Thanks

AWK:
Yes, there is.
Check your textbook, Wikipedia (Self-ionization of water) and Chembuddy's pH calculation lectures

BHAVESH:
I mean natural water bodies having different ion concentration. So if analyze these ions, can we calculate pH using ionic strength of that particular water body?
And Can Van't Hoff Equation be applied here as well???

AWK:
It is enough to calculate the ionic strength, H3O+ ion activity coefficient and apply a precise definition of pH. Condition - water must not contain hydrolyzing ions.

Borek:
Assuming pH is a function of two things only - water autoionization and activity coefficients that depend on the ionic strength - yes, it is enough to knwo concentration of all ions present.

Trick is, with natural waters these assumptions will be never correct, as they contain plenty of acids/bases that change the pH. Almost every ion present, be it cation or anion, reacts with water slightly changing pH. In the case of ions like Na+ or Cl- effects can be safely ignored, in the case of ions like Ca2+ or CO32- - present in every natural water - the effect is quite prominent.

It is actually much easier to just measure pH than to do full analysis of all ions present. Please remember what we measure is not the concentration, but activity of ions, so the pH measured is already corrected for the ionic strength.

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