Limestone

Limestone

Limestone – CaCO3; various forms of lime are used to put on pastures to raise the pH because many soils are naturally acidic. Intensive cropping also lowers the pH. The lime is basic so it neutralises the soil and brings the pH closer to 7.

Quicklime – CaO; formed from limestone in a lime kiln (oven with extremely high temperatures).

CaCO3  (s) -> CaO (s) + CO2 (g)

Slaked Lime – Ca(OH)2; the solid product, in a form of white powder, of the exothermic reaction that occurs when a minimal amount of water is added to quicklime.

CaO (s) + H2O (l) -> Ca(OH)2 (s)

Limewater – a solution of slaked lime in excess water. The slaked lime is only sparingly soluble but produces an alkaline solution containing calcium and hydroxide ions.

Ca(OH)2 (s) <- -> Ca2+ (aq) + 2 OH- (aq)

Mortar – a mixture of slaked lime, sand and water and is a thick paste. It sets when it dries, then over a long period of time becomes hard due to the formation of calcium carbonate as it absorbs carbon dioxide from the atmosphere.

Ca(OH)2 (s) + CO2 (g) -> CaCO3 + H2O (l)

Cement – made from heating limestone with sand and silicates such as clay. It is a mixture of calcium silicates and aluminates. When water is added, a complex series of reactions occur which make it set.