Ionic EquilibriumHard
Question
A buffer solution is prepared in which the concentration of NH3 is 0.30 M and the concentration of NH4+ is 0.20 M. If the equilibrium constant, Kb for NH 3 equals 1.8 × 10-10 , what is the pH of this solution ? (log 2.7 = 0.43)
Options
A.9.43
B.11.72
C.8.73
D.9.08
Solution
pOH = pKb + log 
= - log Kb + log
= - log 1.8 × 10-5 + log
= 5 - 0.25 + (- 0.176)
= 4.75 - 0.176 = 4.57
∴ pH = 14 - 4.57 = 9.43
= - log Kb + log
= - log 1.8 × 10-5 + log
= 5 - 0.25 + (- 0.176)
= 4.75 - 0.176 = 4.57
∴ pH = 14 - 4.57 = 9.43
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