A buffer works by having a weak acid and its conjugate base (like acetic acid and acetate) together in solution. When you add a strong acid, the conjugate base "soaks up" the extra H⁺ ions, turning into the weak acid. When you add a strong base, the weak acid donates H⁺ to neutralize the base, turning into the conjugate base. This keeps the pH from changing much, even when you add acid or base. So, buffers resist pH changes by using this pair to neutralize added acids or bases.

one that can both donate and accept a proton (H⁺), allowing it to act as either an acid or a base according to the Brønsted-Lowry theory.

Strong acid = full dissociation → hydronium = acid concentration

Weak acid = partial dissociation → hydronium < acid concentration

Polyprotic = multiple steps → hydronium slightly > initial concentration