PH of phosphori acid HELP PLEASE

1. Oct 15, 2007

lananh

1. The problem statement, all variables and given/known data
I've been working on this problem and am having issues with some of the problems...

all we learned was that EQ is pH= pka and at eq and EQ1/2 is pk1+pk2/2 which cant even be applied to this question due to x values.

I would GREATLY appreciate ANY help/guidance/etc.

Calculate the pH of 100.0 mL of a 0.110 M phosphoric acid solution being titrated with 0.110 M KOH under the following conditions:

pH = when no KOH has been added. SOLVED 1.598

pH = 2.26 when 50.0 mL of KOH has been added. Hint: Ka1 is not small. (*) SOLVED

pH = when 100.0 mL of KOH has been added.(*)

pH = when 150.0 mL of KOH has been added.

pH = when 200.0 mL of KOH has been added.(*)

pH = when 250.0 mL of KOH has been added. Hint: Ka3 is very small. (*)

pH = 12.29 when 300.0 mL of KOH has been added. SOLVED

pH = when 400.0 mL of KOH has been added.

but all the other 1/2 and eq points im having issues with.. help please!

2. Relevant equations
not ph= pka at EQ and not ph= pka+pka2/2 at 1/2eq

3. The attempt at a solution
(above)