Carbonate system shift with pH

Definition

The balance among carbonic acid, bicarbonate, and carbonate is strongly controlled by pH. Raising pH shifts carbonic acid toward bicarbonate and bicarbonate toward carbonate, while lowering pH reverses the sequence.

As pH rises during neutralization, carbonate reappears, and with calcium already present at high concentration, calcium carbonate can re-form instantly and undo hours of work. This is why over-neutralization caused white scale to precipitate out of solution. The carbonate system is the basis of alkalinity buffering, explored further in the next chapter.

Related concepts

Calcium carbonate solubility · Over-neutralization · Carbonate conversion cascade

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Part of The Blueprint of Water · 🧪 chemistry