When studying the formal theory of acids and bases I came across equations for pH of general acid-base titrations in the work of Robert de Levie.

All articles present the same formalism basically, a good succinct example which shows coverage of acids, bases, ampholytics, and salts, can be found in

- de Levie, Robert. "A general simulator for acid-base titrations." Journal of chemical education 76.7 (1999): 987.

I'm a newbie here so not sure if the better practice would be for me to provide pictures of the equations for example...

My question is, how general is this formalism. In particular, how to define 'total analytical concentration' C for components which are present from multiple different sources. Say for example I mix $C_a$ (NH

_{4})2HPO

_{4} with $C_b$ NH

_{4}H

_{2}PO

_{4}.

The analytical concentration starting for NH

_{4} is $2C_a+C_b$ right? But how do we handle the computation for HPO

_{4} and H

_{2}PO

_{4}, is it

[tex]

C_a* F(HPO

_{4}) + C_b* F(H

_{2}PO

_{4})

[/tex]

or is it

[tex]

(C_a+C_b) *(F(HPO

_{4}) + F(H

_{2}PO

_{4}))

[/tex]