In lab, you're having fun along with buffers based onto a 0.1 M solution of sodium phosphate at pH7.0.  Into this system, there are three of pK_As as:  12.7, 7.21 and 2.12.

Demonstrate a chart indicating the relative amounts of diverse forms of phosphate as (H₃PO₄, H₂PO₄-, HPO₄-², PO₄-³) required to produce buffers of unlike pH. So, for your buffer conditions, please specify the predominant phosphate species present and also the relative amounts of every at equilibrium.

Ans:

[H₂PO₄^-] = 0.0619 M; %H₂PO₄^- = 62%

[HPO₄-²] = 0.0381 M; % HPO₄2^- = 38 %