3) pH Buffer Question. You need to make IL of buffer solution with a pH of 5.3.

Question

3) pH Buffer Question. You need to make IL of buffer solution with a pH of 5.3. You have 15.82 grams of pyridine (you can look up this species). Assume all activity coefficients = 10. a) present a detailed process for constructing this buffer b) calculate the buffer capacity of this buffer c what would be the final equilibrium pH of this buffer solution you prepared if 0.02 moles of HCI were added and allowed to equilibrate, and then 0.03 moles of NaOH were added. 4) Metal lon Buffer Question. As we did in lecture, report the process for ulizing EDTA as a metal ion buffer to prepare a Ga3+ solution with a buffered free [G#1 of 5x10-8M at pH = 7.0.

Explanation / Answer

3) Prepare buffer pyridine/pyridineH+ with pH = 5.3

a. pKa of pyridineH+ = 5.25

initial moles pyridine = 15.82 g/79.1 g/mol = 0.2 mol

let x moles of HCl is added to prepare buffer

then using Hendersen-Hasselbalck equation,

pH = pKa + log(pyridine/pyridineH+)

5.3 = 5.25 + log((0.2 - x)/x)

1.12x = 0.2 - x

x = 0.2/2.12 = 0.094 mol

so moles of HCl needed = 0.094 mol

mass of HCl needed = 0.094 mol x 36.5 g/mol = 3.43 g

moles pyridine in buffer = 0.2 - 0.094 = 0.106 mol

b. buffer capacity = [pyridine] + [pyridineH+]

                            = (0.106 mol/1L) + (0.094 mol/1L) = 0.2 M

c. when HCl = 0.02 mol was added

pH of solution would be,

pH = 5.25 + log[(0.106 - 0.02)/(0.094 + 0.02)]

      = 5.13

when NaOH = 0.03 mol was added

pH of solution would be,

pH = 5.25 + log[(0.106 + 0.03)/(0.094 - 0.03)]

      = 5.58

4) not enough information to solve the problem

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