Phosphoric acid, H3PO4(aq), is a triprotic acid, meaning that one molecule of the acid has three acidic protons. Estimate the pH, and the concentrations of all species in a 0.250 M phosphoric acid solution.
[H3PO4] = ?
[H2PO4^-] =?
[HPO4^2-]=?
[PO4^3-]=?
[H^+]=?
[OH^-]=?
pH=?
4 answers
Tell me what you don't understand about this.
i converted from pKa to Ka for all three values. i don't know where to go from there.
What about looking at the three Ka values seprately? You notice that they are about 10^5 from each other. That means that the (H^+) is determined primarily by the first ionization. The second and third ionization produce little H^+. So do the first calculation as you would a monoprotic acid and (at least for the time being) ignore the second and third. Do that and see if you can see where to go from there.
Ka1 is relatively large; probably you will need to solve the quadratic for Ka1.
0 answers