Question

Calculate the pH and the poH 0.0035moldm-3 H3 PO4 solution

Answer 1

The first ionization is
.................H3PO4 ==> H^+ + H2PO4^-
I..............0.0035...........0...........0
C...............-x.................x............x
E............0.0035-x..........x............x
k1 = (H^+)(H2PO4^-)/(H3PO4)
Look up k1and plug the E line into the equation. Solve for (H^+) a,d convert to pH and pOH.
NOTE 1: You can ignore the H^+ from k2 and k3.
NOTE 2: Probably you will need to solve the quadratic equation; i.e. you will not be able to ignore x in the 0.0035-x above.
Post your work if you get stuck.