Calculate K_b of Conjugate Base from K_w

The dissociation of diprotic acid H₂C₃H₂O₄ is as follows:

K_a1 corresponds to the dissociation of first acid H₂C₃H₂O₄, while K_a2 corresponds to the dissociation of the second acid HC₃H₂O₄^-.

We can calculate base dissociation constant K_b from acid dissociation constant K_a via this formula.

K_w is the ionic product of water and this formula only applies to conjugate acid-base pairs.

Hence to calculate K_b of HC₃H₂O₄^-, we need to use the K_a of its conjugate acid partner H₂C₃H₂O₄.

Therefore answer to this question is option C.

Topic: Ionic Equilibria, Physical Chemistry, A Level Chemistry, Singapore

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