Determine the pH of a buffer solution that is 0.027molL with respect to aqueous NH3

pKb = 4.75 and 0.025 molL with respect to NH4Cl.

Use the Henderson - Hasselbalch equation:

pOH = pKb + log ( [salt]/[base])
pOH = 4.75 + log (0.025/0.027)
pOH = 4.75 + log 0.926
pOH = 4.75 + (-0.03)
pOH = 4.72

pH = 14.00 - 4.72
pH = 9.28