\"What is the pH of Na3PO4? While this is a triprotic species, you may ignore tw

Question

"What is the pH of Na3PO4? While this is a triprotic species, you may ignore two of the Ka's and concentrate on the single Ka that is appropriate for this problem."

I don't even know how to go about starting this. This analytical chemistry course is killing me. Any help would truly be appreciated! There is an appendix in the back of the book with different Ka's for different acids and bases, but nothing that's close to what I'm looking for.

Explanation / Answer

Phosphate does a hydrolysis, ( & you only use the last K): PO4) -3 in water --> HPO4) -2 & OH- Kh = Kw / Ka3 = 1e-14 / 3.6e-13 = 0.0278 0.0278 = [HPO4] [OH-] / [PO4] 0.0278 = [X] [X] / [0.80 - X] 0.0278 [0.80 - X] = X^2 0.0222 - 0.0278 X = X^2 X^2 + 0.0278 X - 0.0222 = 0 X = [OH-] = 0.134 Molar pOH = -.873 14 -pOH = pH = 13.13 your answer: 13.13

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