Chem. Concepts: Buffers

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Chem. Concepts Buffers

• A General Overview
• Eric Liu
• Mr. Michael Gangluff
• Chemistry AP

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What is a Buffer?

• A buffer is a solution that resists changes in pH
• when small amounts of acid or base are added to
  it.

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What is it made of?
Buffers can be placed into two categories acidic
buffers and basic buffers

• Acidic buffers
• Consists of a weak acid and a salt of its
  conjugate base
• e.g. CH3COOH and CH3COONa
• pH less than 7

• Basic buffers
• Consists of a weak base and a salt of its
  conjugate acid
• e.g. NH3 and NH4Cl
• pH greater than 7

Our blood is a buffer, as cells can only survive
within a narrow pH range
The pH of a buffer can be changed by altering the
ratio of acid and its conjugate base or base and
its conjugate acid. The amount of acid/conjugate
base or base/conjugate acid determine its buffer
capacity, or amount of acid or base that can be
added for it to still maintain constant pH
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How does it work?

• Buffers follow one of the following equilibriums
• There are both products and reactants present in
  both cases
• Buffers use Le Chateliers Principle, which
  states that a system will relieve stress put on a
  system by shifting to the left or right side of
  the equation accordingly.
• In other words, if you add reactant to the
  equilibrium, the system would respond by removing
  reactant (and thus creating product), and vise
  versa

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How does it work?
If acid is added to the system

• The H3O from the acid will cause the system to
  shift left
• Or react with OH- to form H2O

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How does it work?
If base is added to the system

• The OH- from the base will cause the system to
  shift to the left
• Or react with H3O to form H2O

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Summary

• Buffers are solutions that resist changes in pH
  with the addition of small amounts of acid or
  base
• They consist of a weak base and its conjugate
  acid salt or a weak acid and its conjugate base
  salt
• They work through Le Chateliers Principle,
  shifting to the left or right to counterbalance
  the addition of acid or base