pH Effect on Carbonate Speciation

Definition

The way pH changes the identity of the dissolved species available, controlling whether carbonate exists to form calcium carbonate.

At low pH, hydrogen ions convert carbonate into bicarbonate and carbonic acid, species that stay dissolved with calcium, so scale is limited. As pH rises, carbonate becomes favored and calcium gains access to the doubly charged carbonate ion that forms a low solubility solid. Raising pH does not strengthen the lattice; it allows the right lattice pieces to coexist, which is why pH is the gatekeeper for calcium carbonate scale.

Related concepts

Precipitation · Temperature Effect on Solubility · Alkalinity

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Part of The Blueprint of Water · 🧪 chemistry