Calcium hydroxide
Calcium hydroxide (traditionally called slaked lime) is an inorganic compound with the chemical formula Ca(OH). It is a colorless crystal or white powder and is obtained when calcium oxide (called "lime" or "quicklime") is mixed, or slaked with water. It has many names including hydrated lime, caustic lime, builders' lime, slack lime, cal, or pickling lime. Calcium hydroxide is used in many applications, including food preparation, where it has been identified as E number E526. Limewater is the common name for a saturated solution of calcium hydroxide.
Nickel compounds
Nickel hydroxides are used in nickel–cadmium and Nickel–metal hydride batteries.
Nickel(II) hydroxide Ni(OH), the main hydroxide of nickel is coloured apple green. It is known as the mineral theophrastite.
β-NiO(OH) is a black powder with nickel in the +3 oxidation state. It can be made by oxidising nickel nitrate in a cold alkaline solution with bromine. A mixed oxidation state hydroxide NiO(OH) is made if oxidation happens in a hot alkaline solution. A Ni hydroxide: nickel peroxide hydrate NiO, can be made by oxidising with alkaline peroxide. It is black, and unstable and oxidises water.