Just as pHpH is the negative logarithm of [H3O+][H3O+], pKapKais the negative logarithm of KaKa
pKa=−logKapKa=−logâ¡Ka
The Henderson-Hasselbalch equation is used to calculate the pHpHof buffer solutions:
pH=pKa+log[base][acid]pH=pKa+logâ¡[base][acid]
Notice that the pHpH of a buffer has a value close to the pKapKaof the acid, differing only by the logarithm of the concentrationratio [base]/[acid][base]/[acid]. The Henderson-Hasselbalchequation in terms of pOH and pKbpKb is similar.
pOH=pKb+log[acid][base]
How many grams of dry NH4ClNH4Cl need to be added to 1.80 LL ofa 0.100 MM solution of ammonia, NH3NH3, to prepare a buffersolution that has a pHpH of 8.85? KbKb 1.8×10−51.8×10−5.
Express your answer with the appropriate units.
