Calcium Carbonate (CaCO₃) — Properties, Uses & Safety

Overview

Calcium carbonate (CaCO3) is an ionic compound with a molar mass of 100.09 g/mol, composed of calcium cations (Ca2+) and carbonate anions (CO32−). It appears as a white powder or crystalline solid and is one of the most abundant minerals on Earth, found naturally as chalk, limestone, marble, travertine, and the shells of marine organisms like clams, oysters, and coral. These different forms represent the same chemical compound in various crystal structures and purities — calcite and aragonite are the two main polymorphs. Calcium carbonate has a melting point of approximately 825 °C (with decomposition) and is only slightly soluble in water (0.013 g/L), though it dissolves readily in acidic solutions with effervescence: CaCO3 + 2 HCl → CaCl2 + H2O + CO2. This acid-base reaction, which produces visible carbon dioxide bubbles, is a classic chemistry demonstration and the basis of the geological acid test for identifying carbonate rocks. When heated strongly, calcium carbonate undergoes thermal decomposition: CaCO3 → CaO + CO2, producing quicklime (calcium oxide) — a reaction fundamental to cement and lime production for thousands of years. Calcium carbonate is widely used as an antacid (Tums), a dietary calcium supplement, a filler in paper and plastics, a whitening agent in paints and coatings, and a key ingredient in cement and concrete manufacturing. It has no significant GHS hazard classifications. For chemistry students, calcium carbonate is a cornerstone compound that illustrates ionic bonding, polyatomic ions, acid-base reactions with gas evolution, thermal decomposition, the carbon cycle, solubility rules, and Le Chatelier's principle (ocean acidification shifts the equilibrium of CaCO3 dissolution). Its presence in geology, biology, industry, and medicine makes it one of the most interdisciplinary compounds in the curriculum.

IUPAC Name

calcium carbonate

CAS Number

471-34-1

PubChem CID

10112

Molecular Formula

CaCO₃

Molar Mass

100.09 g/mol

State at STP

solid

Appearance

White powder or crystalline solid

Physical Properties

Melting Point

825 °C

Density

2.711 g/cm³

Solubility in Water

0.013 g/L at 25 °C

ΔH°f

-1206.9 kJ/mol

ΔG°f

-1128.8 kJ/mol

Composition

Reactions