Calcium carbonate solubility

Definition

Calcium carbonate solubility rides on the carbonate balance, which is strongly controlled by pH. Raising pH shifts bicarbonate toward carbonate, and calcium finds that carbonate and moves toward scale.

Lowering pH keeps the same calcium comfortably dissolved, so two waters at pH 7.8 and 8.6 can read identical on a hardness test yet behave like completely different fluids on a heat exchanger. This pH dependence is the exact trap behind the over-neutralization at 13.4, where white scale precipitated. It is also why neutralization of high-calcium acid must be controlled carefully.

Related concepts

Carbonate system shift with pH · Ionic lattice · pH controls chemistry

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Part of The Blueprint of Water · 🧪 chemistry