Calcium Carbonate

Calcium carbonate — now an essential compound in modern chemistry — was shaping our world long before it even had a name. From the towering pyramids of Egypt to the elegant marble sculptures of ancient Greece, calcium carbonate has been shaping human civilisation for millennia. In this article, we will be understanding this marvellous compound of not just modern but also historical importance. So let’s begin. 

1.0What is Calcium Carbonate?

Calcium carbonate is among the most ubiquitous substances on the planet. It's a white, powdery chalk substance that may look dull at first sight, but it plays a significant role in numerous aspects of our lives. From the blackboard chalk to the shells of sea creatures and even the indigestion tablets we take, calcium carbonate is ubiquitous.

Scientifically, calcium carbonate is a chemical compound. It contains three elements: calcium (Ca), carbon (C), and oxygen (O). When mixed, they form a solid, typically white substance with a very pungent smell. You can see it in rocks, eggshells, snail shells, seashells, pearls, and even in your bones and teeth.

2.0Calcium Carbonate Formula

The chemical formula for calcium carbonate is CaCO₃, where Ca represents Calcium ions, C stands for Carbon, and O means Oxygen ions. The calcium carbonate formula breaks down into two ions Ca²⁺ and CO₃^2–, each of which represents:  

• The carbonate ion has a trigonal planar structure in which one carbon atom is covalently bonded to three oxygen atoms. This structure in the CaCO₃ compound is connected to Calcium (Ca) via a polyatomic ionic bond. 
• Ca²⁺: This is a calcium ion with a +2 charge. It's a metallic cation that comes from group 2 of the periodic table (alkaline earth metals).
• CO₃²⁻: This is the carbonate ion, made up of one carbon (C) atom and three oxygen (O) atoms. The ion carries an overall -2 charge.

So when calcium carbonate is formed, one Ca²⁺ ion combines with one CO₃²⁻ ion to form a neutral compound.

3.0Physical Properties of Calcium Carbonate

*Molar mass or molecular weight of calcium carbonate is the mass of one mole of a compound, calculated by summing the atomic masses of all atoms in that compound. It is calculated in grams per mole (g/mol). 

For example, the mass of each element of one mole of calcium carbonate can be expressed as: 

• Calcium (Ca) = 40.08 g/mol
• Carbon (C) = 12.01 g/mol
• Oxygen (O) = 16.00 g/mol × 3 = 48.00 g/mol

Hence, the molar mass of calcium carbonate, when you add it all up, will be given like this:

40.08 (Ca) + 12.01 (C) + 48.00 (O₃) = 100.09 g/mol

4.0Chemical Properties of Calcium Carbonate

The chemical formula for calcium carbonate is CaCO₃, forming an ionic bond in its structure. The compound is a versatile material forming powerful bonds with different chemicals, such as: 

1. Reaction with Acids: When reacted with acids, Calcium carbonate releases carbon dioxide gas and gives off salt and water as products. 

CaCO_3​ + 2HCl → CaCl₂ ​+ CO₂ ​↑ + H₂​O

2. Thermal Decomposition: Calcium Carbonate undergoes thermal decomposition to form calcium oxide and carbon dioxide when heated strongly: 

CaCO₃ ​ CaO + CO₂​↑

3. Reaction with Water: Although calcium carbonate doesn’t directly react with water, it reacts only when there is carbon dioxide present. It gives off calcium bicarbonate as the product: 

CaCO₃ ​+ H₂​O + CO₂​ → Ca(HCO₃​)₂​

This reaction is important in natural water systems, like the formation of limestone caves or the temporary hardness of water.

5.0Preparation and Formation of Calcium Carbonate

Calcium carbonate is a versatile compound which can either be formed naturally or prepared manually in laboratories or industries. 

Natural Formation of Calcium Carbonate: 

Naturally, the calcium carbonate is formed by thousands of years of geological and biological processes, generally in natural water bodies. The reaction involved in this formation: 

$\mathrm{Ca}(\mathrm{OH}{)}_2+{\mathrm{CO}}_2\to {\mathrm{CaCO}}_3\downarrow +{\mathrm{H}}_2\mathrm{O}$

Laboratory or Industrial Preparation: 

a) From Calcium Hydroxide and Carbon Dioxide (Limewater Test): This is the most common method, which leaves a white milky precipitate confirming the presence of CO₂.

$\mathrm{Ca}(\mathrm{OH}{)}_2+{\mathrm{CO}}_2\to {\mathrm{CaCO}}_3\downarrow +{\mathrm{H}}_2\mathrm{O}$

b) From Calcium Chloride and Sodium Carbonate (Double Displacement Reaction): This method is used industrially to produce ${\mathrm{CaCO}}_3$ as a filler or pigment.

${\mathrm{CaCl}}_2+{\mathrm{Na}}_2{\mathrm{CO}}_3\to {\mathrm{CaCO}}_3\downarrow +2\mathrm{NaCl}$

6.0Where is Calcium Carbonate Located?

Calcium carbonate is mostly a naturally occurring compound which exists in numerous forms and shapes, for example:

• Limestone: It is a sedimentary rock composed predominantly of calcium carbonate, which is mined and used as an important raw material in various industries.
• Marble: A more compact, attractive form of limestone, which is frequently utilised in buildings as well as sculptures.
• Chalk: A soft, powdery form, which was previously widely used on school blackboards.
• Sea animal shells: Corals, snails, and clams all use calcium carbonate to build protective shells.

7.0Calcium Carbonate Uses

The uses of calcium carbonate are numerous across various industries and in everyday life. Let's decompose:

• Antacids: Calcium carbonate is one of the significant ingredients in over-the-counter antacids. It neutralises stomach acid and gives relief from heartburn or indigestion.
• Calcium supplements: It is used to supplement individuals who don't have sufficient calcium from their diet, particularly for bone development.
• Pharmaceutical filler: It's utilised in tablets to provide bulk to them.
• Cement and concrete: Limestone, predominantly calcium carbonate, is subjected to heat and blending to produce cement, the very foundation of the building industry.
• Marble and ornamental stone: Slabs of calcium carbonate marble are employed in flooring, kitchen countertops, and statues.
• Soil treatment: It serves to neutralise the pH of acid soils. Farmers add powdered limestone (calcium carbonate) to neutralise the soil and enable them to grow crops.
• Food additive (E170): It's applied as a white food colour or anti-caking agent in foods such as sugar, chewing gum, or baking powder.
• Processing aid: It's employed in wine and beer manufacture to regulate the acidity.
• Paper making: It is utilised as a filler to provide smoothness and brightness in paper.
• Paints: Applied as a white filler and pigment to enhance consistency.
• Plastic production: Incorporated into plastics to make them stiffer and more durable.

8.0Environmental Significance

Calcium carbonate is also involved in the global carbon cycle. Marine organisms utilise calcium carbonate to build shells. As they perish, the shells settle on the ocean floor and eventually form limestone. The process sequesters carbon for millions of years, maintaining atmospheric carbon dioxide levels in balance. 

Besides these effects on the biosphere, calcium carbonate also forms some of the most spectacular natural architecture, like limestone caves, through its decomposition over millions of years. 

However, this equilibrium is threatened by ocean acidification. When more carbon dioxide flows into the oceans, it decreases the pH of water, making it more difficult for marine animals to construct shells from calcium carbonate.