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Buffering Capacity Addition of STRONG Acids or Bases

Buffering Capacity Addition of STRONG Acids or Bases . What is buffering capacity? What changes to pH occur with addition of strong acids or strong base?. Buffer Characteristics (Qualitative). 1. Buffer Capacity – amount of acid or base the buffer sln can neutralize before pH changes

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Buffering Capacity Addition of STRONG Acids or Bases

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  1. Buffering CapacityAddition of STRONG Acids or Bases What is buffering capacity?What changes to pH occur with addition of strong acids or strong base?

  2. Buffer Characteristics (Qualitative) • 1. Buffer Capacity – amount of acid or base the buffer sln can neutralize before pH changes • 2. Effective pH Range – numeric range over which the buffer acts effectively • Work to resist pH change best when pH = pKa • Use buffers whose acidic form pH ~ pKa

  3. What is buffering capacity? • Goal of a buffer is to keep the pH of a solution within a narrow range. • While the ratio of [A-]/[HA] influences the pH of a solution, the actual concentrations of A-and HA influence the effectiveness of a buffer. • The more A- and HA molecules available, the less of an effect addition of a strong acid or base will have on the pH of a system.

  4. Effect of Strong Acid or Base on Buffer • Assume that all of strong is used up in rxns • Strong completely dissociates, all H+ or OH- • Open text to pg. 711

  5. Practice Exercise • Calculate the pH of a solution that results when 0.10 mol gaseous HClis added to 1 L of a buffered solution containing 0.25 M NH3 (Kb = 1.8 x 10 -5) and 0.40 M NH4Cl. • LIST • THINK • STOICHIOMETRY • H-H Eqnor [H+]eqn

  6. Be a Chemist! Choose a Buffer! • Optimal buffering occurs when [HA] = [A-] • So, when choosing a buffer, you want [A-]/[HA] to be close to 1 • The pKa of the weak acid to be used in a buffer should be as close as possible to the desired pH. Suppose you need a buffered solution with a pH of 4 • Best choice for of a weak acid is one with pKa = 4 or Ka = 1 x 10 -4

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