Calcium Carbonate, Oxide and Hydroxide

Calcium Carbonate, also known as limestone or chalk, is a common substance found in rocks. Its chemical formula is CaCO3.
This compound is insoluble in water but will react with acids to form calcium salt, water, and carbon dioxide. This reaction is an example of a reaction between an acid and a carbonate.
When heated, Calcium Carbonate decomposes to form Calcium Oxide and Carbon Dioxide. The process is called thermal decomposition. The equation for this reaction is: CaCO3 → CaO + CO2
The production of Calcium Oxide is a key industrial process carried out on a massive scale. Calcium Oxide, also known as Quicklime or Burnt Lime, has a chemical formula of CaO.
Calcium Oxide is a white crystalline solid with a melting point of about 2,600°C. It is used in the manufacture of cement, paper, and glass, among other uses.
Calcium Oxide is a strong alkaline substance. When mixed with water, a vigorous reaction occurs producing Calcium Hydroxide and a large amount of heat. This process is known as ‘slaking’.
The chemical equation for the reaction between Calcium Oxide and Water is: CaO + H2O → Ca(OH)2
Calcium Hydroxide is a soft, white crystalline powder with the chemical formula Ca(OH)2. It is also known as Slaked Lime.
Calcium Hydroxide can be dissolved in water to form an alkaline solution known as ‘limewater’. It is used in agriculture to neutralise acidic soils.
An interesting chemical property of limewater is that it turns milky or cloudy when carbon dioxide is bubbled through it. This reaction forms Calcium Carbonate and water, providing a method to test for carbon dioxide. The equation for this reaction is: Ca(OH)2 + CO2 → CaCO3 + H2O
The limestone cycle refers to the series of reactions between calcium carbonate, calcium oxide and calcium hydroxide. Understanding these reactions is important because they demonstrate conservation of mass, as the same calcium ions are present throughout the whole cycle.