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One liter of buffered solution should be prepared with a general concentration of 0.320M with a pH of 5.83 :
- Pyridine solution (formula: C5H5N) in water at a concentration of 1.00M - HCl solution in water at a concentration of 0.85M - Distilled water   In addition, given: pKb (pyridine) = 8.75   What are the volumes to be taken from each ingredient to prepare the buffer?

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asked by jehan
  1. You need two equations to start.
    Here is equation 1 where Py is pyridine and HPy is when HCl is added. Remember that pKa + pKb = pKw = 14 so pKa is 14-8.75 = 5.25
    pH = pKa + log (py/Hpy)
    5.83 = 5.25 + log base/acid
    Solve for B/A.
    Equation 2 is
    A + B = 0.320
    Solve those two equations simultaneously for A and B (acid and base or HPy and Py)

    So you will start with 320 millimoles Py (obviouly that is 320 mL of 1 M Py) and add x mL of 0.85 M HCl to get the final acid concentration you want.
    I assume you can get the rest of this on your own. Post your work if you get stuck. BTW, you won't have a liter of solution when you finish the alculations so you will need to add water to make it up to the desired 1 L.

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    posted by DrBob222
  2. thank you very much for your help

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    posted by jehan

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