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 NH3 equals 1.8 10-5, what is the pH of this solution? ( 2.7 = 0.43)
- 9.08
- 9.43
- 11.72
- 8.73
Answer
(2) 9.43
Solution
For a basic buffer: [OH-] = Kb [NH3][NH4+]
= 1.8 10-5 0.300.20
= 2.7 10-5 M
pOH = - (2.7 10-5)
= 5 - 0.43 = 4.57
pH = 14 - 4.57 = 9.43
Answer: (2)