Given that
pH = 5
so, pOH = 14-pH = 14 - 5 = 9
Now, from the table, weak base having pKb value close to 9 is pyridine with Kb = 1.7 *10-9 na pKb = 8.77
From Henderson- Hasselbach equation
pOH = pKb + log [conjugate acid]/[base]
9 = 8.77 + log [0.34] / [base]
[base] = 0.2 M
Now, Initial molarity (M1) = 1.6 M
Initial volume required (V1) = ?
Final molarity (M2) = 0.2 M
and final volume (V2) = 700 mL
M1V1 = M2V2
V1 = (0.2 M * 700 mL) / 1.6 M = 87.5 mL
Preparing Buffer Solutions: Calculating the Volume of Weak Base Needed Use the table of K values ...
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