Resulting pH of two salts - (Oct/03/2008 )

Dear all,

The following ions H2PO4 and HPO4 are used in a medium and I guess it's used as a buffer, are they acid and base respectively? I see they have pKa values but pKa are only for the dissociation of acids.

What steps should I follow to calculate the resulting pH if I'm given the mass of these salts (say, KH2PO4 and K2HPO4)? I realized that it’s used in many commercial medium.

Thanks

Edit: Come to think of it, H2PO4 ions alone are enough to make a buffer since it's dissociation will yield a HPO4 ion. Perhaps they want to have ratio?

yes, they are considered the acid and base components when preparing the buffer.

there are tables available to give the proportions of each to attain a specific pH.

they also follow the henderson-hasselbach equation (you can find it by searching the forum).