Suppose a strong base is added into an acidic buffer (such as acetic acid buffer) up to the endpoint. This means that the acetic acid molecules neutralize the hydroxide ions to the point that the solution contains mostly acetate ions (with their counter ions, of course), a negligible amount of acetic acid molecules due to Le Chatelier's principle and water.

My question is: can this resulting solution be immediately used as a basic buffer, since it contains a base with its conjugate acid?

Can the same buffer solution be used back and forth in the lab?

  • $\begingroup$ I am confused by the way you describe the use of buffer solutions. I usually know them being used to guard against excessive pH changes in a medium in which something else is being performed. Obviously, that something else would mean that you can’t reuse the buffer. But maybe I am grossly misunderstanding. $\endgroup$ – Jan Oct 3 '17 at 7:06
  • $\begingroup$ Yeah, I'm actually revisiting the basics of the subject of buffers (where you are just playing with buffers and acids\bases to see what happens...), so I thought about this situation. I guess it doesn't really come up in the lab, as you said. But perhaps as an exercise in a buffer teaching lab? Would the question be valid there? $\endgroup$ – Don_S Oct 3 '17 at 7:13
  • $\begingroup$ A buffer is an equimolar mixture of a weak acid and it's conjugate weak base. Right? What you have after adding a lot of strong base is a spent buffer solution, which has practically no conjugate acid. $\endgroup$ – Karl Oct 3 '17 at 10:38
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    $\begingroup$ In principle, your suggestion works though you should recognize that the buffer is not active until you have added enough of the other component to bring it back to the buffer range. There's no reason in practice that anyone would want to do this, since it's much easier just to create a new buffer solution. $\endgroup$ – Zhe Oct 3 '17 at 13:59

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