How do we calculate the pH of a buffer that is composed of HPO24 and H2PO4?

1 Answer
Apr 13, 2017

The buffer equation tells us that pH=pKa+log10([HPO24][H2PO4]), but here pKa=7.20 for H2PO4.

Explanation:

A buffer is formed by mixing appreciable quantities of a weak acid and its conjugate base. Such a mixture keeps the pH of the solution tolerably close to the pKa of the weak acid.

Now this site gives pKa=7.20 for the following reaction:

H2PO4+H2O(l)HPO24,

And thus solutions which contain tolerably equal concentrations of dihydrogen phosphate, and biphosphate, should have pH reasonably close to 7.20.