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Buffered Solutions

Buffered Solutions. What is a buffer? Calculations involving Buffers. What are buffers?. Buffers are solutions of a weak conjugate acid-base pair . They are particularly resistant to pH changes , even when strong acid or base is added. Buffer Solutions.

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Buffered Solutions

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  1. Buffered Solutions What is a buffer? Calculations involving Buffers

  2. What are buffers? • Buffers are solutions of a weak conjugate acid-base pair. • They are particularly resistant to pH changes, even when strong acid or base is added.

  3. Buffer Solutions • Consist of a weak acid and its salt • HF and NaF • Consist of a weak base and its salt • NH3 and NH4Cl

  4. How are they resistant to pH changes?How do buffers “work” ? • If we mix a weak acid (HA) with its conjugate base (A-), both the acid and base components remain present in the solution. • This is because they do not undergo any reactions that significantly alter their concentrations. • The weak acid and weak base remain in the solution with high concentrations since they rarely react with the water.

  5. How do buffers “work”? • The acid/conjugate base may react with one another, HA + A- → A- + HA, but when they do so, they simply trade places and the concentrations [HA] and [A-] do not change. • In addition, HA and A-rarely react with water. • Weak acid rarely dissociates in water (will rarely lose its proton H+ to water). • Conjugate base is weak, it rarely steals a proton H+ from water.

  6. Example • A buffered solution contains 0.50 M acetic acid (Ka = 1.8 x 10 -5) and 0.50 M sodium acetate. Calculate the pH of this solution.

  7. Equilibrium and Buffers • pH of Buffers determined by two factors: #1. value of Ka for the weak acid/base (Ka) #2. ratio of concentrations of conjugate acid/ base pair [HA] / [A-] Henderson –Hasselbach Equation

  8. Sample Exercise 17.3 p. 709 • Common Ion Effect, neglect x • LIST • THINK • ICE • SOLVE

  9. Henderson-HasselbachEqn • Can be used when the ratio is known [HA]/[A-] • Can be used when Ka or Kb is known (pKa)

  10. Sample Exercise 17.4 p. 710 • Work Backwards using Kb and [OH-] • Get out Buffers Made Easy Handout! • Let’s watch and learn!

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