Calcium carbonate NEW

Calcium carbonate is a chemical compound with the formula CaCO₃. Here's a breakdown of its key chemical characteristics:

Chemical Formula: CaCO₃

• This indicates it contains one calcium (Ca) atom, one carbon (C) atom, and three oxygen (O) atoms per formula unit.

• It's an ionic compound formed by the calcium cation (Ca²⁺) and the carbonate anion (CO₃²⁻).

  Chemical Structure:

• Calcite: Trigonal crystal system.

• Aragonite: Orthorhombic crystal system (common in shells).

• Vaterite: Hexagonal crystal system (less stable).

• The carbonate ion (CO₃²⁻) has a trigonal planar structure, with the carbon atom in the center bonded to three oxygen atoms.

• The calcium ions (Ca²⁺) are electrostatically attracted to the carbonate ions, forming a crystal lattice.

• It exists in several different polymorphs (crystal structures), the most common and stable being:

  Chemical Properties:

• Appearance: Typically a white, odorless powder or colorless crystals. The color in nature (e.g., colored marble) comes from impurities.

• Solubility: Very poorly soluble in pure water. However, its solubility increases significantly in water containing dissolved carbon dioxide (CO₂) because it forms soluble calcium bicarbonate (Ca(HCO₃)₂):
  CaCO₃ (s) + CO₂ (g) + H₂O (l) → Ca²⁺ (aq) + 2HCO₃⁻ (aq)

• Reaction with Acids: Reacts readily with acids (even weak ones like acetic acid in vinegar) to produce carbon dioxide gas (effervescence), water, and a calcium salt:
  CaCO₃ (s) + 2H⁺ (aq) → Ca²⁺ (aq) + CO₂ (g) + H₂O (l)
  This is a key identifying reaction.

• Thermal Decomposition: Decomposes at high temperatures (around 825°C) into calcium oxide (quicklime) and carbon dioxide:
  CaCO₃ (s) → CaO (s) + CO₂ (g)

  Occurrence:

• Limestone: Primarily composed of calcite.

• Chalk: A soft, fine-grained limestone formed from microscopic marine organisms.

• Marble: Metamorphosed limestone (recrystallized).

• Travertine: Formed by precipitation from mineral springs.

• Biological: The primary component of shells of marine organisms (oysters, clams, snails, corals), pearls, eggshells, and the skeletons of some plankton.

• Geological: A major component of sedimentary rocks:

  Key Uses (Driven by its Chemical Properties):

• Dietary calcium supplement.

• Antacid (neutralizes stomach acid).

• Food additive (E170) for coloring or firming.

• Filler in pharmaceuticals.

• Filler in paper, paint, plastics, rubber.

• Raw material for producing quicklime (CaO) and slaked lime (Ca(OH)₂).

• Flux in smelting iron ore.

• Construction: Crushed stone (limestone, marble), cement ingredient, dimension stone (marble).

• Agriculture: Soil conditioner to neutralize acidity (lime).

• Manufacturing:

• Health & Food:

• Environmental: Used in flue gas desulfurization to remove sulfur dioxide (SO₂).

In summary, calcium carbonate (CaCO₃) is a ubiquitous ionic compound formed from calcium and carbonate ions. Its relatively low solubility in water (except in acidic conditions), its vigorous reaction with acids producing CO₂, and its thermal decomposition are defining chemical characteristics. Its abundance in biological structures and geological formations makes it one of the most common minerals on Earth, with wide-ranging industrial and biological importance.