Kalkwasser
From ReefPedia
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[edit] KalkwasserCalcium hydroxide Molecular formula: Ca(OH)2 |
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Introduction
Calcium hydroxide, also known as slaked lime, is a chemical compound with the chemical formula Ca(OH)2. 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 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,[1] calcium hydroxide decomposes into calcium oxide (CaO) and water. A suspension of fine calcium hydroxide particles in water is called milk of lime. The clear solution of calcium hydroxide is called limewater. The term "Kalkwasser" was coined by Peter Wilkins and literally means, "limewater" in German. Kalkwasser is considered to be a medium strength base.
Limewater can be made by dissolving either calcium oxide (CaO) or calcium hydroxide (Ca(OH)2) in water. When (CaO) is used, it first hydrates to Ca(OH)2 on contact with water (H2O):
(1) CaO + H2O → Ca(OH)2 + heat
Consequently, there is little difference between using CaO and Ca(OH)2 except that (CaO) gives off a substantial amount of heat when it hydrates. When these materials dissolve, they dissociate in the water to calcium ions (Ca++) and hydroxide ions (OH-):
(2) Ca(OH)2 → Ca++ + 2OH
Limewater turns milky if carbon dioxide is passed through it, due to precipitation of calcium carbonate. Kalkwasser powder and Kalkwasser solutions should be stored in a sealed container. Once Kalkwasser powder is mixed with water, all particulate matter should be allowed to settle to the bottom for at least one hour before dosing to an aquarium.
Kalkwasser solution needs to be added slowly to the tank and to an area with a lot of circulation. Dripping slowly ensures that the pH of the tank water is not raised too fast. Dripping into an area of high circulation ensures the Kalkwasser solution is dispersing quickly, to avoid a local high concentration, which may result in precipitation of calcium carbonate solids. Kalkwasser can be dosed at any time in the day, however, dosing at night helps to counteract the typical lowering of pH that occurs in reef tanks at night during the lights out period.
FAQ
Commonly asked questions regarding Kalkwasser.
