Calcium bicarbonate, also called calcium hydrogen carbonate, has a chemical formula Ca(HCO₃)₂. The term does not refer to a known solid compound; it exists only in aqueous solution containing the calcium (Ca), bicarbonate (HCO₃), and carbonate (CO₃) ions, together with dissolved carbon dioxide (CO₂). The relative concentrations of these carbon-containing species depend on the pH; bicarbonate predominates within the range 6.36-10.25 in fresh water.