Calcium carbonate is insoluble in water.
Elementary calcium reacts with water at room temperature, according to the following reaction mechanism:
Ca (s) + 2H2O (g) → Ca(OH)2 (aq) + H2 (g)
This reaction forms calcium hydroxide that dissolves in water as a soda and hydrogen gas. Calcium compounds are more or less water-soluble. When compounds are insoluble in water, the general reason is that the bonding within that species is stronger than the bonding between it and water.
- Calcium carbonate has very low solubility in pure water (15 mg/L at 25°C), but in rainwater saturated with carbon dioxide, its solubility increases due to more soluble calcium formation bicarbonate.