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Buffered Solutions

Buffered Solutions. Pg 585 - 586. 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!

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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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