Question

please can someone explain why strong
acids cant be used as buffers?

Answer 1

Buffers, by definition, are solutions that resist changes in pH when something is added.
Take a strong acid, HCl, for example:


Because HCl is a strong acid, the Cl- will not stick to H+ at all. Cl-'s like: "heck no, I don't need to stick to any H+, I'm perfectly stable by myself thankyouverymuch."

So if you dumped some H+ in a solution of HCl/Cl-, it will not resist any change in pH because the Cl- is such an incredibly weak very weak (almost neutral) base.

On the other hand, CH3COOH (acetic acid) is a weak acid. and it's conjugate is strong-ish.

If you dumped some H+ in a solution of CH3COOH/CH3COO-, some H+ will stick to the CH3COO- but there will still be CH3COO-. So you will have both the acid and the conjugate base, thus resisting a drastic change in pH
.