Determine the pH of a solution that is generated when 2.623 g Na3PO4 is added to a 100mL of 0.0800 M H3PO4.

Answer 1

I would use
k1k2k3 = (H^+)^3(PO4^3-)/(H3PO4)
Plug in for PO4^3- and H3PO4 and solve for (H^+) then convert to pH.

Answer 2

I use the Given concentrations? and solve for [H3O]?

Answer 3

right. mols Na3PO4 = grams/molar mass and M = mols/L solution.
H3PO4 is given.
Solve for H^+ and convert to pH.