Recall that EDTA exists in various forms depending on the pH of the solution. Among the different forms, the fully unprotonated species is thought of as the one that chelates with metal ions. So, the formation constant expression for a metal–EDTA complex considers only the fully unprotonated form of EDTA, which predominates only at high pH. At any given pH, different forms of EDTA are in equilibrium, and the concentrations of these forms sum to the total concentration of uncomplexed EDTA. So, the fraction of EDTA in the fully unprotonated form is needed. Rearranging this expression and substituting it in the formation constant equation gives a modified factor termed the conditional formation constant. The fraction of EDTA in the fully unprotonated form is a constant at a given pH, so the conditional formation constant is pH-dependent. The higher the pH, the higher the conditional formation constant, and the more stable the metal–EDTA complex.