Upsetting Buffers

Dealing with acidic and/or basic buffers.
The buffer is upset by the addition of a small amount of either strong acid or strong base.

Acidic Buffer:
HA  +  H2O  <=>   H3O+   +  A-
  add strong acid (H3O+), llbm shifts to left (reactant) side
    thus [HA] increases, [A-] decreases
  add strong base (OH-), llbm shifts to the right (product) side
     {Why? OH- joins with H3O+ to create H2O}
    thus decreasing [HA], increasing [A-]

Basic Buffer:
Base + H2O  <=>  BaseH+   +   OH-
    add strong acid (H3O+), llbm shifts to right (product) side
           {Why? OH- joins with H3O+ to create H2O}
       thus [Base] decreases,  [BaseH+] increases
    add strong base (OH-), llbm shifts to the left (reactant) side
    thus increasing [Base], decreasing [BaseH+]

Typical Question:
500.0mL of a 0.10M NH3/0.080M NH4Cl solution has 3.00mL of 3.00M NaOH added. Determine the pH of the resulting solution.

-write the llbm reaction for the weak (in this case weak base NH3)
-determine the concentration change of the strong (base in this example) will undergo as it is added to the buffer solution (c1V1=c2V2)**
-organize and ICE chart to track changes to the two components of the buffer (the weak and its salt)
-calculate [OH-] at llbm, (since it is a basic buffer in this example)
-determine pOH
-finally determine pH

**since a small amount of strong base is being added to a much larger volume, the strong base concentration will be greatly impacted.
However the addition of a few mLs to the much larger buffer volume will have negligible impact on the initial buffer concentrations
-buffer concentrations are impacted by the llbm shift that results from the addition of the strong base (or acid)

Homework: From the Buffer/Neutralization/Titration Handout
5,6,7,8
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