Buffers

  1. Buffers are chemical equilibrium systems that resist wide changes in pH.
  2. You can create a buffer by dissolving a weak acid and its conjugate base into the same solution.
  3. For example, if acetic acid (HC2H3O2) and (NaC2H3O2) were dissolved into the same solvent then you would create a buffer.
    1. The conjugate base of HC2H3O2 is C2H3O2-1, so by dissolving NaC2H3O2 into water you get plenty of C2H3O2-1 ions (the conjugate base).
    2. The sodium ions don't play any role so we will leave them out of the chemical equation:
      HC2H3O2(aq) H+1(aq) + C2H3O2-1(aq)
    3. Notice this is the same as the equilibrium equation for the dissociation of acetic acid with a Ka of 1.8 x 10-5
    4. Given such a small kA, not many acetate ions will form naturally. However, by adding sodium acetate, a large number these ions will be present. So, once we set up the buffer there will be a large number of undissociated HC2H3O2 and a large number of C2H3O2-1 ions.
    5. Now consider adding a strong acid to this equilibrium system (addition of a H+1 donor). According to Le Chetalier what will happen to this system?
    6. Now consider adding a strong base to this equilibrium system (addition of a H+1 acceptor). Anything with OH-1 ions will dissolve to react with the H+1 ions to form H2O. According to Le Chetalier what will happen to this system?
  4. The importance of buffers can not be emphasized enough. Without buffers we would not be able to maintain the proper pH of our blood. Blood pH must remain between 7.35 and 7.45 or we might die.
  5. There are several buffer systems in our bodies which help to maintain our proper pH levels. One of them involves our breathing.
  6. Our blood contains significant amounts of both carbonic acid (H2CO3) and its conjugate base, the bicarbonate ion (HCO3-1). This creates the equilibrium system: H2CO3(aq) + H2O(l) H3O+1(aq) + HCO3-1(aq)
  7. Carbonic acid also forms the equilibrium:
    H2O(l) + CO2(aq) H2CO3(aq)
  8. By combining these two equations we get:
    2 H2O(l)+CO2(aq)H2CO3(aq)+H2O(l)H3O+1(aq)+HCO3-1(aq)
  9. As our body's metabolic processes produce acids, equilibrium is shifted from right to left and we exhale the CO2, maintaining proper levels of all chemicals.
  10. You can raise your blood pH by hyperventilating which removes excessive amount of carbon dioxide causing the entire system of equilibrium equations to shift left removing hydronium ions from the system. If you hyperventilate for too long you could enter Alkalosis.

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