Calcium is a reducing metal that does not exist in nature as a elementary substance. It usually forms compounds with other substances, such as calcium oxide, calcium hydroxide and calcium carbonate.
Calcium carbonate
Calcium carbonate is a chemical compound with the formula CaCO₃. It is a common substance found in rocks, such as limestone and chalk. It also occurs in eggshells, snail shells, and the shells of marine animals such as clams and oysters. It will be corroded by acid. It breaks down into carbon dioxide and calcium oxide at high temperatures.
CaCO₃(s) + 2HCl(aq) → CaCl₂(aq) + H₂O(l) + CO₂(g)
Calcium oxide
Calcium oxide, commonly known as quicklime or burnt lime, is a widely used chemical compound. It is a white, alkaline crystalline solid at room temperature. Quicklime reacts with water to produce slaked lime and gives off a lot of heat. It will even boil if there is not too much water. Calcium oxide is hygroscopic and is often used as a desiccant and dehydrating agent. It is also used to heat food in the field.
CaCO₃(s) → CaO(s) + CO₂(g)
CaO(s) + H₂O(l) → Ca(OH)₂(aq)
Calcium hydroxide
Calcium hydroxide, also known as slaked lime or hydrated lime, is a white powder that is the raw materials for cement, and an important chemical raw material for many industries. It is formed by mixing calcium oxide with water. This compound is slightly soluble in water. It can react with acid and acidic oxide. Calcium carbonate is produced when there is not enough carbon dioxide. Calcium bicarbonate is produced when there is sufficient carbon dioxide.
Ca(OH)₂(aq) + H₂SO₄(aq) → CaSO₄(s) + 2H₂O(l)
Ca(OH)₂(aq) + CO₂(g) → CaCO₃(s) + H₂O(l)
Ca(OH)₂(aq) + 2CO₂(g) → Ca(HCO₃)₂(aq)