Question

pH= 7.44
What is the ratio of [H2PO4^-]/[HPO4^2-]

What does the pH become if 25% of the hydrogen phosphate ions are converted to the dihydrogen phosphate ion?

What does the pH become if 15% of the dihydrogen phosphate ions are converted to hydrogen phisphate ions?

Use the Henderson-Hasselbalch equation.
pH = pK2 + log [(base)/(acid)].
a) solve for the ratio directly.
b) choose a convenient number for the acid, use the ratio to calculate the base. Then decrease base by 25% and add that number of mols to acid. Recalculate pH using the HH equation.
c) similar to part b.