I have looked at several sources including Khan Academy, ChemCollective and the answer to a similar question: Can someone please explain buffers to me?
However, it is not clear whether buffers can only protect against the opposite species. I.e. a weak acid can only protect against the pH change caused by strong bases, or if it can also protect against the pH change caused by strong acids.
This is my thought:
If we have $\ce {H_2CO_3_{(aq)} + H_2O_{(l)}<=>H_CO^{-}_3_{(aq)} + H_3O^+_{(aq)}}$
Then we add a strong acid $\ce{HCl + H_2O-> H_3O^+ + Cl^-}$
Then we have $x$ amount of protons in the solution and for every one of the weak acid's conjugate base, there is a proton. So, to me it appears that there is no way for the weak acid to act as a buffer for a strong acid. Is this correct or am I missing something?