Final answer:
To find the mass of K₃PO₄ for a buffer with pH 12, one would use the Henderson-Hasselbalch equation. Specific values such as pKa and K₃PO₄'s molar mass are necessary for the calculation, which are not provided.
Step-by-step explanation:
To determine the mass of K₃PO₄ needed to prepare a buffer solution with a pH of 12 using 1 L of a 0.1M K₂HPO₄(aq) solution, we can use the Henderson-Hasselbalch equation:
pH = pKa + log([A^-]/[HA])
The equation involves the pKa value of the weak acid (HPO4^2-, from K₂HPO₄) and the ratio of the concentrations of the conjugate base (PO4^3-, from K₃PO₄) to the acid (HPO4^2-). However, the specific pKa value for the relevant dissociation step of phosphoric acid and the final formula mass of K₃PO₄ would be required to calculate the exact mass.
Since these values are not provided in the question, we cannot calculate the precise amount without them. General steps would be to calculate the needed [PO4^3-] from the desired pH and pKa, determine the moles of PO4^3- needed, and then convert this to grams of K₃PO₄ using its molar mass.
Without the necessary values to solve the problem, we can guide students in the right direction but cannot provide an exact numerical answer.