(1) pKa of acetic acid = 4.75
From Henderson equation
pH = pKa + log {[Conjugate base] / [Acid]}
pH = 4.75 + log {[NaC2H3O2] / [HC2H3O2]}
pH = 4.75 + log (0.125 / 0.100)
pH = 4.75 + log 1.25
pH = 4.75 + 0.097 = 4.85
pH = 4.85
(2) pKb of pyridine= 8.75
We know from Henderson equation
pOH = pKb + log {[Conjugate acid] / [Base]}
pOH = 8.75 + log{[pyridinium hydrochloride] / [pyridine]}
pOH = 8.75 + log(0.010 / 0.006)
pOH = 8.75 + log 1.67 = 8.75 + 0.22 = 8.97
pH = 14.00 - pOH = 14.00 - 8.97 = 5.03
pH = 5.03
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