Carbon and its Compounds


Calcium carbonate \(CaCO_3\) is one of the most known chemicals. Calcium carbonate is a non-toxic and odourless compound. \(CaCO_3\) is found as a white mineral that occurs naturally in chalks, limestones and marbles. It is a common substance present in rocks as the mineral’s calcite and aragonite. CaCO3 is most notably limestone. It is a type of sedimentary rock that mainly consists of calcite and is the main component of eggshells,  snail shells,  seashells and pearls. Calcium Carbonate has medical use too as if as a calcium supplement or as an antacid. Though excessive consumption of calcium carbonate is hazardous and cause poor digestion.


Chemistry of \(CaCO_3\)

Calcium carbonate shares the typical properties of other carbonates as given below:

\(CaCO_3(s) + 2 H^+(aq) \rightarrow  Ca{2+}(aq) + CO_2(g) + H_2O(l)\)

  • It releases carbon dioxide upon heating. It is a thermal decomposition reaction, or calcination to above \(840^oC in the case of CaCO_3\), to give calcium oxide, commonly known as quicklime, with reaction enthalpy 178 kJ/mol.

\(CaCO_3(s) \rightarrow CaO(s) + CO_2(g)\)

  • Calcium carbonate reacts with water that is saturated and with carbon dioxide to form the soluble calcium bicarbonate.

\(CaCO_3(s) + CO_2(g) + H_2O(l) \rightarrow  Ca(HCO_3)_2(aq)\)

This reaction is important in the erosion of carbonate rock, forming caverns, and results to hard water in many regions.

  • An unusual form of calcium carbonate is the hexahydrate, ikaite, i.e., \(CaCO_3·6H_2O\). Ikaite is stable only at a temperature below \(8^oC\).

Preparation of \(CaCO_3\) (Calcium carbonate)

The vast majority of calcium carbonate is in use in industry and is extracted by mining or quarrying. The pure form of calcium carbonate as if for food or pharmaceutical use is produced from a pure quarried source. This source is usually marble.

\(CaCO_3\) is obtained with the help of carbon dioxide and slaked lime as raw materials. When carbon dioxide is allowed to pass through slaked lime as a result calcite is obtained.

Calcium carbonate is prepared with the help of calcium oxide. Water is added to provide calcium hydroxide and later carbon dioxide is passed through this solution. It is done to precipitate the desired calcium carbonate, referred to in the industry as precipitated calcium carbonate (PCC):

\(CaO + H_2O → Ca(OH)_2\)

\(Ca(OH)_2 + CO_2 → CaCO_3 \downarrow  + H_2O\)

Uses of \(CaCO_3\)

Some common uses of calcium carbonate are given below.

  • Calcium carbonate plays an important role in construction, be it as a building material such as marble or as an ingredient in cement.
  • Calcium carbonate is in use in medicinal industries. Industries manufacture antacids, tablets made of base materials etc.
  • It is in use as calcium supplements.
  • Calcium carbonate is in use in the manufacture of paints, paper, plastics, etc.

FAQs on \(CaCO_3\)

Question 1: What are the applications of calcium carbonate.

Answer: The applications are:

  • Calcium carbonate is largely in use in the pulp and paper industry. It can be in use as a filter and pigment, making possible the production of a whiter, as if higher quality pigment than other minerals.
  • Calcium carbonate is in use in the construction industry as a filler in concrete, as if increasing its durability and appearance and purifying metals for use in construction applications.
  • It is present in fertilizers to provide calcium to plants and pH stabilization of the soil.
  • Calcium carbonate is an additive to food products for livestock animals and humans. It is a supplement in vitamins.
  • Calcium carbonate in water and sewer treatment plants is in use to remove the acidity and impurities.

Question 2: What are the properties of calcium carbonate.

Answer: The properties are:

  • Calcium carbonate is a fluffy powder.
  • It easily decomposes to produce carbon dioxide when heated up to 1200K.
  • When calcium carbonate reacts with dilute acid, it gives carbon dioxide as a by-product.

\(CaCO_3 + H_2SO_4 \rightarrow  CaSO_4 + H_2O + CO_2\)

  • At 1200K, it decomposes to give carbon dioxide and calcium oxide.
    \(CaCO_3 \rightarrow  CaO + CO_2\)
  • On reacting with dilute acids, it gives carbon dioxide.
    \(CaCO_3 + 2HCl \rightarrow  CaCl_2 + H_2O + CO_2\)
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