[billitar]

im trying to calculate the pka of  based on experimental data in the form of absorbance at 450nm. the absorbance naturally changes with pH.

I have been trying to manipulate Beer's Law and the H-H buffer equation to awnser this question, but to no avail.

[Tetrahedrite]

Beer's law only hold true between specific concentrations (ie absorbances). Maybe you're outside the range?