If a buffer solution is 0.130 M in a weak base (K_b = 3.1 Times 10^-8) and 0.440

Question

If a buffer solution is 0.130 M in a weak base (K_b = 3.1 Times 10^-8) and 0.440 M in its corrugate add what Is the pH? A weak base ionizes as follows. B(aq) + H_2O(l) BH^+ (aq) + OH^- (aq) You can convert K_b to pK_a,. then use the Henderson- Hasselbalch equation to find pH, or you can just use the K_b expression to find (OH^-], then convert that to a pH. For a buffer, you can assume that the initial concentrations of B and BH^+ are equal to their equilibrium concentrations. Thus, you can plug the given values directly into the K_b expression.

Explanation / Answer

This is a basic buffer so

pOH = pKb + log(Hb+/B)

pOH = -log(3.1*10^-5) + log(0.44/0.13) = 5.0381

pH = 14-pOH = 14-5.0381 = 8.9619

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