‘What is the pH of 0.50 M H2S (given that Ka = 8.91 × 10−8)?

H2S ==> H+ + HS-
Ka = [H+][HS-]/[H2S] = 8.91×10^-8
(x)^2/0.5 = 8.91×10^-8
x^2 = 4.445×10^-8
x = 2.11×10^-4 = [H+]
pH = -log 2.11×10^-4
pH = 3.68

pH = 0.5(pKa – lg(1)) = 7.05*0.5 = 3.55

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