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Chemistry Question on Equilibrium

For a polybasic acid, the dissociation constants have a different values for each step, e.g., H3A<=>H++H2A− {H3A <=> H+ +H2A^-} ; K=Ka1K=K_{a_1} H2A−<=>H++H2A2− {H2A- <=> H+ +H2A^{2-}} ; K=Ka2K=K_{a_2} HA2−<=>H++A3− {HA^{2-} <=> H+ +A^{3-}} ; K=Ka3K=K_{a_3} What is the observed trend of dissociation constants in successive stages?

A

Ka1>Ka2>Ka3K_{a_1} > K_{a_2} > K_{a_3}

B

Ka1=Ka2=Ka3K_{a_1} = K_{a_2} = K_{a_3}

C

Ka1<Ka2<Ka3K_{a_1} < K_{a_2} < K_{a_3}

D

Ka1=Ka2+Ka3K_{a_1} = K_{a_2} + K_{a_3}

Answer

Ka1>Ka2>Ka3K_{a_1} > K_{a_2} > K_{a_3}

Explanation

Solution

The values of dissociation constants for successive stages decrease.