Calcium bicarbonate

Calcium bicarbonate is the dissolved ionic compound Ca(HCO₃)₂, formed when carbon dioxide-rich water dissolves calcium carbonate. It contributes to temporary water hardness and can decompose into calcium carbonate, carbon dioxide, and water.

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Carbonic acid: Carbonic acid is the weak acid formed when carbon dioxide dissolves in water. It supplies the acidity that helps carbon dioxide-rich water dissolve calcium carbonate.
Temporary hardness: Temporary hardness is water hardness caused mainly by dissolved calcium and magnesium bicarbonates. Calcium bicarbonate is a principal source of this removable form of hardness.
Bicarbonate: Bicarbonate is the polyatomic ion HCO₃⁻, an intermediate form in the carbonic acid system. Two bicarbonate ions pair with one calcium ion in the dissolved compound.
Calcium sulfate: Calcium sulfate is an ionic compound composed of calcium and sulfate ions. It can cause permanent hardness, unlike hardness associated with bicarbonate that heating can reduce.
Calcium carbonate: Calcium carbonate is an ionic compound found in limestone, chalk, and many shells. Its dissolution in carbon dioxide-rich water produces dissolved calcium and bicarbonate ions.
Water softening: Water softening is the removal or reduction of dissolved minerals that cause hardness. Treatments target calcium ions supplied by bicarbonate-bearing hard water.
Calcium ion: The calcium ion is the divalent cation Ca²⁺, common in minerals and natural waters. Its positive charge balances the two bicarbonate ions.
Sodium bicarbonate: Sodium bicarbonate is the soluble ionic compound NaHCO₃, commonly called baking soda. It contains the same bicarbonate ion but does not supply calcium hardness.
Carbon dioxide: Carbon dioxide is a colorless gas composed of one carbon atom and two oxygen atoms. Dissolved carbon dioxide drives the formation of bicarbonate-bearing water.
Limescale: Limescale is a hard deposit composed mostly of calcium carbonate, formed from mineral-rich water. Heating can precipitate calcium carbonate from water containing calcium bicarbonate.