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Buffered Solutions

Buffered solutions play a crucial role in maintaining pH stability, even when strong acids or bases are introduced. For instance, when 0.001 mol of HCl is added to pure water, its pH falls sharply from 7 to 2, a change of 5 units! However, the same addition to a 0.1 M acetic acid and sodium acetate solution results in a minor pH shift from 4.74 to 4.66. A buffered solution typically contains a weak acid and its conjugate base, which work together to resist significant pH changes by neutralizing added H+ or OH- ions, demonstrating essential buffering characteristics.

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Buffered Solutions

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  1. Buffered Solutions Pg 585 - 586

  2. Buffers • Buffered solution = resists a change in pH • EVEN when a strong acid or base is added! • Examples: • When 0.001 mol of HCl is added to 1L of pure water, the water’s pH drops from 7 to 2 • A pH change of 5 units! • When 0.001 mol of HCl is added to a solution of 0.1M acetic acid (HC2H3O2) and 0.1M sodium acetate (NaC2H3O2), the pH change is from 4.74 to 4.66 • A pH change of 0.08 pH units

  3. What makes a buffered solution? • A solution is buffered by the presence of a weak acid and its conjugate base • Example of a buffered solution: • An aqueous solution of acetic acid and sodium acetate • HC2H3O2, NaC2H3O2 • NaC2H3O2 Na+, C2H3O2- • Buffering capacity: measured by how much H+ or OH- the buffer can absorb without a significant change in the pH of the solution

  4. What are the characteristics of a buffer? • The solution contains a weak acid and its conjugate base • The buffer resists changes in pH by reacting with any H+ or OH- added • These ions cannot accumulate! • Any added H+ reacts with the base A- • H+ + A- HA • This produces a weak acid that will only slightly change the overall pH of the solution • Any added OH- reacts with the weak acid HA • OH- + HA  H2O + A-

  5. How does a buffer work? • What happens when we add HCl to a buffered solution? (NaC2H3O2) • HCl  H+ + Cl- • NaC2H3O2  Na+ + C2H3O2- • H+ + C2H3O2-  HC2H3O2 (weak acid!)

  6. How does a buffer work? • What happens when we add the NaOH to a buffered solution? • NaOH  Na+ + OH- • HC2H3O2 + OH-  H2O + C2H3O2- • The OH- has a strong affinity for the H+ in acetic acid, water will be produced instead of having the OH- concentration increase!

  7. Determine the following buffer systems:

  8. Which of the following pairs would work as a buffer system? • HNO2, NaNO3 • H2SO4, NaOH • HF, KF • HCl, NaCl • Answer  HF and KF

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