Buffer Capacity


1 M NaOH(aq) is added incrementally to beakers containing deionized water, and 0.01 M, 0.1 M, and 1 M acetic acid-acetate buffer solutions to which Universal Indicator has been added.  Also, 1 M HCl(aq) is added incrementally to the water and to the acetic acid-acetate buffer solutions.  The color of the indicator in the deionized water changes dramatically with the addition of a single drop of acid or base.  The three buffer solutions of 0.01 M, 0.1 M, and 1 M all will resist the change in pH when small amounts of acid and or base are added.  The 1 M buffer solution, on the other hand, has to be transferred to a larger beaker to accommodate the acid/base addition before the solution begins to change color!

Buffer capacity demonstration set-up image

Buffer capacity is defined after the presentation of the demonstration.

Curriculum Notes 
This demonstration is good for showing the concept of buffer capacity in a general chemistry class. About 10 minutes of class time is necessary.
One day of lead time is required for this project.

Web page authors: Randy Sullivan and T. Greenbowe, University of Oregon.  This page is under construction.

Buffer capacity of a buffer solution is the ability of the buffer to neutralize incoming acid and or base and maintain a pH.  The concentration of the weak acid and the conjugate base, in the case of an acidic buffer, determines the buffer capacity.

As described above.


  • 4 ea. 150 mL beakers containing 100 mL of the following solutions: 0.5 M Acetic Acid/0.5 M Sodium Acetate, 0.05 M Acetic Acid/0.05 M Sodium Acetate, 0.005 M Acetic Acid/0.005 M Sodium Acetate, each with a couple of dropperfuls of universal indicator solution added and a stir bar in the beaker.
  • stir plate
  • 1 ea. large dropper bottle of 1 M NaOH.
  • 1 ea. 250 mL bottle containing 1 M NaOH.
  • 1 ea. 400 mL beaker containing a stir bar.


  • Place the beaker of DI water on the stir plate and turn on and adjust the stir plate.
  • Add a couple of drops of 1 M NaOH to the solution until it changes to violet.
  • Repeat with the remaining solutions, proceeding to the next higher buffer concentration each time.  it will require more and more base to effect the change each time.
  • By the time you get to the IM buffer solution, you will need to transfer the solution to the 400 mL beaker to accomplish the change.

Safety Precautions 

  • Always wear goggles when performing chemistry demonstrations.
  • If you get base on your hands, rinse thoroughly with water.
  • I you get base in your eyes flush with copious amounts of water.

Prep. Notes 
As described above.

Randy's Notes
This demonstation has a great "wow" factor.  The demonstration maintains the attention of students. I like to ham it up by acting like I'm getting bored with adding the acid or base dropwise to the 1 M acetic acid-acetate buffer solution, and then add it by the dropperful.  Then I get bored with adding it by the dropperful and pour directly from the dropper bottle.  When that runs out, I pull out the 250 mL bottle and start pouring from that.

An alternate presentation of buffer capacity using a didactic approach is found on the followintg URL:

Buffer capacity demonstration didactic lecture V3