is this a buffer system?

Question

Deionized water can have a pH of 7 and considered neutral. If an acid (i.e. HCl) is added the pH quickly decreases. If a base is added the pH quickly increases. Is this a buffer system? Why or why not?

Answer 1

No, it is NOT a buffer system. A buffer system, by definition, will resist small changes in pH upon addition of either an acid or a base. This is NOT the case here because the pH decreases when acid is added and increases when base is added. In order to be a buffer, there must be present a weak acid plus the salt (conjugate base) of that acid, or a weak base and the salt (conjugate acid) of that base.