Calcium

Calcium: the essentials

 Brief description: calcium as the element is a grey silvery metal. The metal is rather hard. Calcium is an essential constituent of leaves, bones, teeth, and shells. Calcium is the fifth most abundant element in the earth's crust and makes up more than 3% of the crust. Calcium does not occur as the metal itself in nature and instead is found in various minerals including as limestone, gypsum and fluorite. Stalagmites and stalactites contain calcium carbonate (CaCO₃). Calcium carbonate is the basis of the cement industry.

Calcium is classified chemically as one of the alkaline earth elements (that is, in Group 2 of the periodic table. The metal is rather reactive. It readily forms a white coating of calcium nitride (Ca₃N₂) in air. It reacts with water and the metal burns with a yellow-red flame, forming largely the nitride.

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Isolation

Isolation: calcium metal is readily available commercially and there is no need to make it in the laboratory. Commercially it can be made by the electrolysis of molten calcium chloride, CaCl₂.

cathode: Ca²⁺(l) + 2e^- → Ca

anode: Cl^-(l) → ¹/₂Cl₂ (g) + e^-

The calcium chloride is made by the action of hydrochloric acid upon calcium carbonate. Calcium chloride is also a byproduct in the Solway process used to make sodium carbonate.

CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂

Alternatively, and on small scale, calcium can be made through the reduction of CaO with aluminium or of CaCl₂ with sodium metal

6CaO + 2Al→ 3Ca + Ca₃Al₂O₆

CaCl₂ + 2Na→ Ca + 2NaCl

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