Show the equilibrium of different species of CO2 dissolved i

Show the equilibrium of different species of CO₂ dissolved in water.

Solution

The first step is to dissolution of CO₂ (g) in H₂O

CO₂ (g) + H₂O -> CO₂ (aq)

The second step is that the CO₂ (aq) forms Carbonic acid when it reacts with H₂O

CO₂ (aq) + H₂O <----------> H₂CO₃ (aq) (Carbonic acid)

The formed carbonic acid cannot be dissociated completely.

H₂CO₃ (aq) <---------> H⁺ + HCO₃^- (aq) (K_a1 ) = dissociation constant)

HCO₃^- <---------> H⁺ + CO₃^-2 (aq) (K_a2 = second dissociation constant)

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