Question

2. The weak base B (Kb = 1.0 * 10-5) equilibrates between water (phase 1) and benzene (phase 2). (a) Define the distribution coefficient, D, for this system. (b) Explain the difference between D and K, the partition coefficient. (c) Calculate D at pH 8.00 if K = 50.0,(d) Will D be greater or less at pH 10 than at pH 8? Explain why.

Answer 1

Part (a). The distribution coefficient (D) = [B]_{phase 2}/{[B]_{phase 1} + [BH⁺]}

Where [B]_{phase 2} is the concentration of weak base in benzene.

[B]_{phase 1} is the concentration of the weak base in water.

And [BH⁺] is the concentration of the proton-abstracted base species.

Part (b). The partition coefficient (K) = [B]_{phase 2}/[B]_{phase 1}