The successive equilibrium constants for the stepwise dissociation of a tribasic acid are K₁ , K₂ and K₃ , respectively. The equilibrium constant for the overall dissociation is

Step-by-step solution

For a tribasic acid like H ₃ PO ₄ has three ionisation constant. The overall ionisation constants (K) will be product of ionisation constants of three steps, i.e. K=K₁ K₂ K₃ H ₃ PO ₄ H ⁺+ H ₂ PO ₄⁻ H ₂ PO ₄⁻ H ⁺+ HPO ₄²⁻ HPO ₄²⁻ H ⁺+ PO ₄³⁻ Adding Eqs. (i), (ii) and (iii), we get gathered H ₃ PO ₄ 3 H ⁺+ PO ₄³⁻ K= [ PO ₄³⁻ ] [ H ⁺ ]^3 [ H ₃ PO ₄ ] gathered Multiply mathematical Eqs. (i), (ii) and (iii), we get gathered K₁ K₂ K₃= [ H ⁺ ] [ H ₂ PO ₄⁻ ] [ H ₃ PO ₄ ] [ H ⁺ ] [ HPO ₄²⁻ ] [ H ₂ PO ₄⁻ ] [ H ⁺ ] [ PO ₄³⁻ ]