Calcium Carbonate

**Molecular formula:** CaCO₃ **Molar mass:** 100,086 g/mol **Description:** Calcium carbonate is a white, crystalline substance that is only slightly soluble in water. It is an ionic compound composed of calcium cations (Ca²⁺) and carbonate anions (CO₃²⁻). In the presence of carbon dioxide and water, calcium carbonate dissolves to form calcium bicarbonate through the following reaction: CaCO₃+ CO₂ + H₂O → Ca(HCO₃)₂. This reversible reaction is responsible for the natural formation of stalactites and stalagmites in caves. **Applications:** Calcium carbonate is widely used as a fertilizer and in the construction industry. Upon heating, it decomposes to produce calcium oxide (CaCO₃ → CaO + CO₂), commonly known as burnt lime. When calcium oxide reacts with water (CaO + H₂O → Ca(OH)₂), it forms calcium hydroxide, also known as slaked lime. Slaked lime is a key component in lime mortar, which is made by mixing slaked lime, sand and water. **Occurrence:** In nature, calcium carbonate is found in limestone rocks, which are mainly composed of the minerals calcite and aragonite. It is a common and widely distributed mineral on Earth.