A pair of molecules that can be converted into each other

A typical buffer system consists of a weak acid and its conjugate base. When a small amount of acid is added, the conjugate base is responsible for catching hydrogen ions; when a small amount of base is added, the weak acid can supplement the hydrogen ions.

Buffer capacity is not unlimited

The buffer's concentration and acid-base ratio determine how much shock it can withstand. Once capacity is exceeded, pH can still change rapidly.

Both experimentation and life require buffering

Cell environment, fermentation process, pharmaceutical preparation and analytical experiments all require the use of buffer systems to control pH within an appropriate range.