Question

how can one find the pH of a solution, given NaHPO4, Na2HPO4 and NaCl all in a beaker filled with water (the volumes of the bases are all the same = 300ml and water added = 100ml to give 1 L solution) known values are, Kb's of the respective bases and all at equilibrium temperature..please help! would like to share some ideas and methods to solve this

Answer 1

write dissociation's for them, simply consider how much H+ or OH- they introduce into the solution (using the Kb's) and add these up. Then use the pH relation to hydronium ion concentration (or hydroxide to pOH).


Ignore NaCl (unless you're taking into account ionic strength).

Answer 2

thank you, i was thinking of that, but a) it seemed too obvious for the credits being awarded and b) should one not consider the fact that HPO4 is diprotic

Answer 3

maybe they want you to find the pH with the activity of H3O+ not the concentration?
H2PO4^- is diprotic not HPO4^2-..

Answer 4

did they give you the concentrations for the solutions of H2PO4^- and HPO4^-2?