What compound is the principal scale former?

The principal scale former in many contexts, particularly in water treatment, heating systems, and plumbing, is calcium carbonate. This compound typically precipitates out of solution when water with high levels of dissolved calcium ions is heated or evaporated. As water temperature increases or as it loses water through evaporation, the solubility of calcium carbonate decreases, leading it to form scale.

Scale formation occurs when the hardness of water (mainly due to calcium and magnesium ions) reacts chemically under certain conditions, causing calcium carbonate to crystallize. This crystallized substance adheres to surfaces within pipes, boilers, and other equipment, leading to reductions in efficiency and potential equipment failures if not properly managed.

The other compounds mentioned have different roles. Potassium carbonate is more soluble and not typically associated with significant scale formation. Magnesium sulfate, while it can contribute to hardness, is less common as a scale former compared to calcium carbonate. Sodium carbonate can precipitate but does not predominantly contribute to scale in the same manner as calcium carbonate. Thus, calcium carbonate's role as a principal scale former is well-documented in both practical and theoretical contexts within environmental health and water chemistry.