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Glossary

Hydroxide

Hydroxides are salt-like substances that contain negative lattice components (anions) in the form of hydroxide ions (OH-). Soluble hydroxides such as sodium hydroxide and potassium hydroxide form strong alkaline solutions (alkalis) with water. These are known as sodium hydroxide or potassium hydroxide. Less soluble hydroxides, e.g. barium hydroxide and calcium hydroxide form weak alkaline suspensions with water. The saturated solutions are called barite or lime water. If these two substances come into contact with carbon dioxide, they become cloudy. In the chemical laboratory, metal hydroxides are generally prepared by adding salt solutions with sodium or potassium hydroxide solution and then filtering off the precipitates, washing and air-drying them. In some cases, pure hydroxides are not formed in this process, but – after precipitation – oxide hydroxides, e.g. iron (III) oxide-hydroxide.