The pH of a 1.00 10-3 M solution of pyrrolidine is 10.82. Calculate Kb.?

Answer 1

Pyrrodiline is a weak base that reacts with water:

B + H2O <==> BH+ + OH-

pH = 10.82, pOH = 14 - pH (at 25 oC), pOH = 14 - 10.82 = 3.18

[BH+] = [OH-] = 10^(-3.18) = 6.6*10^(-4) M

[B] = 10^(-3) - 6.6*10^(-4) = 3.4*10(-4) M

Kb = [BH+] * [OH-] /[B] = 6.6*10^(-4) * 6.6*10^(-4) / 3.4*10^(-4)

Kb = 1.28*10^(-3) or 1.3*10^(-3) approx.