A buffer solution is prepared in which the concentration of NH₃ is 0.30M and the concentration of NH⁴⁺ is 0.20 M. If the equilibrium constant, 
for NH₃ equals 1.8 × 10⁻⁵, what is the pH of this solution ? (log 2.7 = 0.433).
(a) 9.08
(b) 9.43
(c) 11.72
(d) 8.73
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(b) 9.43
pOH = pKb + log([salt]/[base])
= - log(1.8×10^-5) + log(0.2/0.3)
= 4.57
pH = 14 - pOH = 14 - 4.57 = 9.43
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