[tvfields]

How are acid dissociation constants determined (measured), especially in the case of a polyprotic acid like H3PO4?  Is this discussed online, and if so, where?  I am under the impression that the answer might involve measurements of pH, osmotic pressure and electrical conductivity, but I don't know enough details to satisfy my curiousity.

[Borek]

Do you know how they are determined for a monoprotic acids? Quite often the same methods can be used for multiprotic acids.

Note there is no single method - there are many ways to skin that cat.

[ParaChase]

The acid dissociation constant is unique for each ion. H3PO4 will have a much larger Ka than H2PO4 1-, which in turn will have a much larger Ka than HPO4 2-. These individual values can be found online or in a table. Does that help?

[Borek]

These individual values can be found online or in a table. Does that help?

I strongly doubt "find in a table" qualifies as "determine".

[ParaChase]

I strongly doubt "find in a table" qualifies as "determine".

You misunderstood the wording of my answer. The "does that help?" does not have to do with looking up in tables; I meant for that to refer to my earlier statement.

[Borek]

I was referring to

These individual values can be found online or in a table.

And I still support what I wrote: "find in a table" doesn't qualify as "determine".