Calcium carbonate is one of the most popular chemicals which is first encountered in school classrooms, where the use of chalk (form of CaCO3) is found. It is found in the earth’s crust. It is also found in many forms such as marble, limestone, etc. Although they are available in various forms they are chemically similar and only differ physically. They are also referred to as calcite.
What is Calcium Carbonate?
- It is a chemical compound with the formula CaCO3.
- It is a white insoluble powder-like substance which occurs naturally in minerals, chalk, marble, limestone, calcite, shells, pearl, etc.
- Medicinally, it is used as an antacid or as a calcium supplement. It is also used as fillers in cosmetics. It is added to swimming pools as a disinfectant agent and as pH corrector.
- It finds extensive usage in the manufacturing industry as a building material (marble), ingredient for quick lime and cement.
- On the large scale, it is prepared by passing carbon dioxide gas through calcium hydroxide (slaked lime). However, if carbon dioxide is passed in excess, it forms the soluble calcium hydrogen-carbonate.
Ca(OH)2 + CO2→ CaCO3 + H2O
- At 1200K, calcium carbonate decomposes to give carbon dioxide and calcium oxide.
CaCO3 → CaO + CO2
- On reacting with dilute acids, calcium carbonate gives carbon dioxide.
CaCO3 + H2SO4 → CaSO4 + H2O +CO2
Preparation of CaCO3
CaCO3 is obtained by using carbon dioxide and slaked lime as raw materials. When carbon dioxide is passed through slaked lime, calcite is obtained. Another method to obtain calcite is by adding sodium carbonate to calcium chloride.
\(~~~~~~~~~~~~~~~~~\)Ca (OH)2 + CO2 → CaCO3 + H2O
\(~~~~~~~~~~~~~~~~~\)CaCl2 + Na2CO3 → CaCO3 + 2NaCl
When carbon dioxide is passed in excess it leads to the formation of calcium hydrogen-carbonate.
Properties of CaCO3
- It is a fluffy powder.
- It has low solubility in water.
- It decomposes to give carbon dioxide when heated up to 1200K.
- When it reacts with a dilute acid, it liberates carbon dioxide as a by-product.
\(~~~~~~~~~~~~~~~~~\)CaCO3+H2SO4 → CaSO4+H2O+CO2
Uses of calcium carbonate
- It plays an important role in construction, be it as a building material (marble) or as an ingredient in cement.
- It is used in medicinal industries which manufacture antacids, tablets which are made of base materials etc.
- It is used as calcium supplements.
- It is used in the manufacture of paints, paper, plastics, etc.