Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references
Calcium hydroxide, also known as slaked lime, is a chemical compound with the chemical formula Ca(OH)2. It is a colourless crystal or white powder, and is obtained when calcium oxide (called lime or quicklime) is mixed, or "slaked" with water. It can also be precipitated by mixing an aqueous solution of calcium chloride and an aqueous solution of sodium hydroxide. A traditional name for calcium hydroxide is slaked lime, or hydrated lime. The name of the natural mineral is portlandite.
If heated to 512°C, calcium hydroxide decomposes into calcium oxide and water. A suspension of fine calcium hydroxide particles in water is called milk of lime. The solution is called lime water and is a medium strength base that reacts violently with acids and attacks many metals in presence of water. It turns milky if carbon dioxide is passed through, due to precipitation of calcium carbonate.
Because of its strong basic properties, calcium hydroxide has varied uses, such as
A flocculant, in water and sewage treatment and improvement of acid soils
An ingredient in whitewash, mortar, and plaster
An alkali used as a lye substitute in no-lye hair relaxers
A chemical depilatory agent found in Nair
An ingredient in baby formula milk
A chemical reagent
In the reef aquarium hobby for adding bio-available calcium in solution for calcium-using animals such as algae, snails, hard tube worms, and Corals (often referred to as Kalkwasser mix)
In the tanning industry for neutralization of extra acid
In the petroleum refining industry for the manufacture of additives to oils (salicatic, sulphatic, fenatic)
In the chemical industry for manufacture of calcium stearate
In the food industry for processing water (for alcoholic and soft drinks)
For clearing a brine of carbonates of calcium and magnesium in the manufacture of salt for food and pharmacopoeia
In Native American and Latin American cooking, calcium hydroxide is called "cal". Corn cooked with cal becomes nixtamal which significantly increases its nutrition value, and is also considered tastier and easier to digest.
In chewing Betel nut or coca leaves, calcium hydroxide is usually chewed alongside to keep the alkaloidstimulants chemically available for absorption by the body
In the petrochemical industry for manufacturing solid oil of various marks
In the manufacture of brake pads
In the manufacture of ebonite
For preparation of dry mixes for painting and decorating