Alkali metal hydroxide
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The alkali hydroxides are a class of
chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one element ...
s which are composed of an alkali metal cation and the
hydroxide Hydroxide is a diatomic anion with chemical formula OH−. It consists of an oxygen and hydrogen atom held together by a single covalent bond, and carries a negative electric charge. It is an important but usually minor constituent of water. I ...
anion (OH−). The alkali hydroxides are: *
Lithium hydroxide Lithium hydroxide is an inorganic compound with the formula LiOH. It can exist as anhydrous or hydrated, and both forms are white hygroscopic solids. They are soluble in water and slightly soluble in ethanol. Both are available commercially. While ...
(LiOH) * Sodium hydroxide (NaOH) *
Potassium hydroxide Potassium hydroxide is an inorganic compound with the formula K OH, and is commonly called caustic potash. Along with sodium hydroxide (NaOH), KOH is a prototypical strong base. It has many industrial and niche applications, most of which exp ...
(KOH) *
Rubidium hydroxide Rubidium hydroxide is the inorganic compound with the formula RbOH. It consists of rubidium cations and an equal number of hydroxide anions. It is a colorless solid that is commercially available as aqueous solutions from a few suppliers. Like ot ...
(RbOH) *
Caesium hydroxide Caesium hydroxide is a strong base (pKa= 15.76) containing the highly reactive alkali metal caesium, much like the other alkali metal hydroxides such as sodium hydroxide and potassium hydroxide. Caesium hydroxide is corrosive enough to quickly ...
(CsOH)


Production

Alkali hydroxides are formed in the reaction between alkali metals and water. A typical school demonstration demonstrates what happens when a piece of an alkali metal is introduced to a bowl of water. A vigorous reaction occurs, producing
hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic ...
gas and the specific alkali hydroxide. For example, if sodium is the alkali metal: :Sodium + water → sodium hydroxide + hydrogen gas :2 Na + 2 H2O → 2 NaOH + H2 Sodium hydroxide is an important industrial chemical, where it is produced by the
chloralkali process The chloralkali process (also chlor-alkali and chlor alkali) is an industrial process for the electrolysis of sodium chloride (NaCl) solutions. It is the technology used to produce chlorine and sodium hydroxide (caustic soda), which are commodit ...
.


Properties and uses

The alkali metal hydroxides form white crystals that are
hygroscopic Hygroscopy is the phenomenon of attracting and holding water molecules via either absorption or adsorption from the surrounding environment, which is usually at normal or room temperature. If water molecules become suspended among the substan ...
and readily soluble in water, generating large amounts of heat upon dissolution. The solubility increases down the column as the alkali metal ions become larger and the lattice enthalpies decrease. All alkali metal hydroxides are strong bases, meaning that they dissociate completely in solution to give ions. As strong bases, alkali hydroxides are highly corrosive and are used in
cleaning product Cleaning agents or hard-surface cleaners are substances (usually liquids, powders, sprays, or granules) used to remove dirt, including dust, stains, bad smells, and clutter on surfaces. Purposes of cleaning agents include health, beauty, removing ...
s. Sodium hydroxide is readily available in most hardware stores in products such as a
drain cleaner A drain cleaner is method for unblocking sewer pipes or clogged wastewater drains. The term may also refer to a mechanical device such as a plumber's snake, drain auger, toilet plunger, or similar device. Occasionally, the term is applied to a pl ...
. Similarly, potassium hydroxide is available as a solution used for cleaning terraces and other areas made out of wood. Both NaOH and KOH are also used in the production of soap and detergents (
saponification Saponification is a process of converting esters into soaps and alcohols by the action of aqueous alkali (for example, aqueous sodium hydroxide solutions). Soaps are salts of fatty acids, which in turn are carboxylic acids with long carbon chains. ...
). Due to their hygroscopic properties, alkali hydroxides are used as desiccants. They also readily absorb carbon dioxide and are therefore used in
carbon dioxide scrubber A carbon dioxide scrubber is a piece of equipment that absorbs carbon dioxide (CO2). It is used to treat exhaust gases from industrial plants or from exhaled air in life support systems such as rebreathers or in spacecraft, submersible craft or ...
s.


References

Hydroxides Alkali metals {{Inorganic-compound-stub