Question

Why aren't buffers made with 1:1 ratio of acid and conj.base? Wouldn't 1:1 give a better buffering capacity both ways? for example the PBS buffer only has 0.24g/L of KH₂PO₄ while Na₂HPO₄ has 1.42g/L. So why are they made like that? Isn't it better when both of them have the same g/L ?

This also means that the PBS buffer is better at resisting strong acidic stuff correct?

Answer 1

We try to achieve a certain pH, when constructing a buffer

for instance if we want pH = 7.4, which is required for biological processes,

we only have H2PO4- = HPO4- equilibirum, with pKa = 7.21

therefore, we typically adjust acid/base conjguates into forcing pH = required

this will of course not always be 1:1 ratio

pH = pKa + log(A-/HA)

A/HA ratio chanc change for our convenienc ein order to favour a certain pH

note that, as you state, PBS fuffer with a 1:1 ratio will require "support" much more acid H+, addition.

Yet, the pH set point is still important