Carbonic acid (H₂CO₃) is a diprotic acid, meaning it can donate two protons (H⁺). It has two dissociation constants, Ka1 and Ka2, representing each step of proton donation.

Here are the equations for the dissociation constants of carbonic acid:

1. First dissociation:

H₂CO₃(aq) ⇌ H⁺(aq) + HCO₃⁻(aq)

Ka1 = [H⁺][HCO₃⁻] / [H₂CO₃] = 4.3 × 10⁻⁷

2. Second dissociation:

HCO₃⁻(aq) ⇌ H⁺(aq) + CO₃²⁻(aq)

Ka2 = [H⁺][CO₃²⁻] / [HCO₃⁻] = 4.7 × 10⁻¹¹

Note: The values of Ka1 and Ka2 are given at 25°C.