Polyprotic acids contain more than one dissociable proton. Each dissociation ste

Question

Polyprotic acids contain more than one dissociable proton. Each dissociation step has its own acid-dissociation constant, K_a1, K_a2, etc. For example, a diprotic acid H_2A reacts as follows: H_2A(aq) + H_2O(1) H_3O^+ (aq) + HA^- (aq) K_a1 = [H_3O^+] [HA^-]/[H_2A] HA^- (aq) + H_2O(l) + H_3O^+(aq) + A^2- (aq) K_a2 = [H_3O^+] [A^2-]/[HA^-] calculate the equilibrium concentration of H_3O^+ in a 0.40 M solution of carbonic acid Express your answer to two significant figures and include the appropriate units. Calculate the equilibrium concentration of CO_3^2- in a 0.40 M solution of carbonic acid Express your answer to two significant figures and include the appropriate units.

Explanation / Answer

in general for diprotic acid A-2 concentration = Ka2 .

Ka1 for carbonic acid = 4.5×10–7
Ka2 for carbonic acid = 4.7×10–11

so

[CO3-2] = Ka2 = 4.7×10–11 M -------------------------->answer

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