How does increasing ionic strength affect the pH of solution?
Answers
By definition pH is based on activity of a solution an not the concentration of H+. At 25 degrees and 1 atm: Kw={H+}{OH-}/{H2O} and {H+}={OH-} {H+}=(Kw)^0.5 pH= -0.5*logKw= 7.00 At colder temps (e.g. 4 degrees), the van T'off equation applies to the relationship between temperature and reaction rate at an assumed constant enthalpy. pH=7.37 At increased ionic strength (usually < 0.1M; e.g. NaCl) activity can be assumed to be ~1 still, so the pH shouldn't change and = 7.00 At higher ionic strength, the Debye-Huckel Equation applies, and activity (gamma) changes: log gamma= -Az2*I0.5; where A=0.5 at 25 degrees, z= charge, I= ionic strength So in sea water where I= 0.5-0.7M, the pH will increase because activity increases: So pH= 8.08 to 8.33 on various scales depending on the inclusion of various anionic hydrogen complexes (e.g. HSO4-)