Calcium Carbonate

Calcium carbonate (CaCO3) is an inorganic chemical compound made up of calcium, carbon, and oxygen. Under normal temperatures and pressures, this diatomic chemical looks like a fine white powder and is mostly tasteless and odourless.

Physical description

Calcium carbonate is a white, odourless powder and can even take the form of colourless crystals. Practically insoluble in water, it can be found in rocks. The mining of limestone yields ground calcium carbonate. When extracted, the carbonate retains a high degree of purity and may be used as a fine powder or as a slurry. Precipitated calcium carbonate is a byproduct of the Solvay procedure or is manufactured industrially by decomposing limestone to calcium oxide and then recarbonising it (which is used to make sodium carbonate). When it comes to purity, precipitated calcium carbonate is superior to ground calcium carbonate.

Calcium carbonate is the main component of eggshells, gastropod shells, seashell skeletons, and pearls. It is also found in shellfish bones and pearls. Calcium carbonate is created by hard water calcium ions combining with carbonate ions to form a limescale. Despite its medical uses as a calcium supplement or antacid, excessive use can cause hypercalcemia and digestive issues.

Chemical properties of calcium carbonate

Molecular weight: 100.09 g/mol

Number of hydrogen bond donors: 0

Number of hydrogen bond acceptors: 3

Number of rotatable bonds: 0

Number of heavy atoms: 5

Number of isotope atoms: 0

Types of calcium carbonate

Calcite, aragonite, and vaterite are the three polymorphic forms of calcium carbonate that may be found in the earth’s crust.

Calcite

Calcite is the least soluble and the least stable form of calcium carbonate. It is a mineral found in sedimentary, metamorphic, and igneous rocks such as limestone and marble. It is widely used in many sectors, including building, agriculture, and pharmaceuticals.

Vaterite

Vaterite has a hexagonal form. While less stable than calcite and aragonite, it has a higher solubility than these minerals. It may be found in nature in various places, including springs, organic tissue, urinary calculi, gallstones, and plants. It is used in regenerative drugs as well as personal care items.

Aragonite

Aragonite is more soluble and less stable than calcite. It is formed by biological and physical processes in both freshwater and marine environments. Aragonite feeds the sea’s biodiversity and helps keep pH levels in check. It removes pollutants like zinc, cobalt, and lead from wastewater.

Structure of calcium carbonate

Under typical circumstances, the hexagonal -CaCO3 crystal structure is the most thermodynamically stable structure of calcium carbonate (mineral calcite). Other forms of calcium carbonate may be created, including the denser (2.83 g/cm3) orthorhombic -CaCO3 (found in aragonite) and hexagonal -CaCO3 (found in vaterite), which is less dense. Aragonite may be formed through precipitation at temperatures greater than 85 degrees Celsius, while vaterite can be formed through precipitation at temperatures less than 60 degrees Celsius. Calcium atoms in calcite are linked by six oxygen atoms; calcium atoms in aragonite are linked with nine oxygen atoms. Calcite is composed of calcium atoms coordinated with six oxygen atoms. The structure of vaterite is still not completely known. While both strontium carbonate (SrCO3) and barium carbonate (BaCO3) accept the calcite structure, magnesium carbonate (MgCO3) adopts the aragonite structure, which reflects the greater ionic radius of strontium carbonate and barium carbonate.

Preparation of calcium carbonate

A large proportion of the calcium carbonate used in industries is mined or quarried from the earth’s crust. Solid calcium carbonate (for culinary or medicinal applications, for instance) can be manufactured from a pure quarry resource (usually marble).

1) As raw materials, slaked lime and carbon dioxide are mostly used to produce calcium carbonate. Calcite is formed when a carbon dioxide molecule is transported through slaked lime and evaporated. Another technique of obtaining calcite is adding sodium carbonate into calcium chloride, which is a chemical reaction.

CaCl2 + Na2CO3 → CaCO3 + 2NaCl

Ca (OH)2 + CO2 → CaCO3 + H2O

Calcium hydrogen-carbonate is formed when excessive quantities of carbon dioxide are released.

2) It is possible to produce it on a big scale by flowing carbon dioxide gas over calcium hydroxide solution (otherwise called slaked lime). Nevertheless, if there is an excessive amount of carbon dioxide going through, it leads to the creation of soluble calcium hydrogen-carbonate, which is toxic.

Ca (OH)2 + CO2→ CaCO3 + H2O

Chemical reactions

Calcium carbonate exhibits many of the same characteristics as other carbonates. These include:

● When it comes into contact with acids, it releases carbon dioxide

CaCO3(s) + 2 H+(aq) → Ca2+(aq) + CO2(g) + H2O(l)

● The thermal breakdown of calcium carbonate occurs when the compound is heated to above 840 degrees Celsius, producing calcium oxide (commonly known as quicklime), with enthalpy of the process equal to or more than 178 kilograms per mol of calcium carbonate.

CaCO3(s) → CaO(s) + CO2(g)

● Calcium carbonate combines with carbon dioxide-saturated water to generate soluble calcium bicarbonate, then soluble in water again.

CaCO3(s) + CO2(g) + H2O(l) → Ca(HCO3)2(aq)

Conclusion

Calcium carbonate is used in architecture and buildings in the form of marble. It is also present in several types of cement. Further, it is used in tile and mortar manufacturing, coatings and other corrosion inhibitors, adhesives and paints, and so on. Calcium carbonate also neutralises acids.