Buffer Capacity

1 M NaOH is added incrementally to beakers containing DI water, and 0.01 M, 0.1 M, and 1 M acetate buffer solutions to which universal indicator has been added.  The DI water changes dramatically with the addition of a single drop.  The 1 M buffer solution, on the other hand, has to be transferred to a larger beaker to accommodate the acid/base addition before it begins to change!

Curriculum Notes 

This demo is good for showing buffer capacity in a general chemistry class. About 10-15 minutes.

Lead Time 
One day of lead time is required for this project.

This demo has a great "wow" factor.  I like to ham it up by acting like I'm getting bored with adding the acid or base dropwise, 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.


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.

© Copyright 2012 Email: Randy Sullivan, University of Oregon Chemistry Department and UO Libraries Interactive Media Group