Calcium hydride is the

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 ...

with the formula , an alkaline earth hydride. This grey powder (white if pure, which is rare) reacts vigorously with water, liberating

hydrogen Hydrogen is a chemical element; it has chemical symbol, symbol H and atomic number 1. It is the lightest and abundance of the chemical elements, most abundant chemical element in the universe, constituting about 75% of all baryon, normal matter ...

gas. is thus used as a drying agent, i.e. a desiccant. is a saline hydride, meaning that its structure is salt-like. The alkali metals and the alkaline earth metals heavier than beryllium all form saline hydrides. A well-known example is sodium hydride, which crystallizes in the NaCl motif. These species are insoluble in all solvents with which they do not react. crystallizes in the ( cotunnite)

structure A structure is an arrangement and organization of interrelated elements in a material object or system, or the object or system so organized. Material structures include man-made objects such as buildings and machines and natural objects such as ...

Preparation

Calcium hydride is prepared from its elements by direct combination of calcium and hydrogen at 300 to 400 °C.

Uses

Reduction of metal oxides

is a reducing agent for the production of metal from the metal oxides of Ti, V, Nb, Ta, and U. It is proposed to operate via its decomposition to Ca metal: :

Hydrogen source

has been used for hydrogen production. In the 1940s, it was available under the trade name "Hydrolith" as a source of hydrogen:

The trade name for this compound is "hydrolith"; in cases of emergency, it can be used as a portable source of hydrogen, for filling airships. It is rather expensive for this use.

The reference to "emergency" probably refers to wartime use. The compound has, however, been widely used for decades as a safe and convenient means to inflate weather balloons. Likewise, it is regularly used in laboratories to produce small quantities of highly pure hydrogen for experiments. The moisture content of diesel fuel is estimated by the hydrogen evolved upon treatment with CaH.

Desiccant

The reaction of with water can be represented as follows: : The two hydrolysis products, gaseous and , are readily separated from the dried solvent. Calcium hydride is a relatively mild desiccant and, compared to molecular sieves, probably inefficient. Its use is safer than more reactive agents such as

sodium Sodium is a chemical element; it has Symbol (chemistry), symbol Na (from Neo-Latin ) and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 element, group 1 of the peri ...

metal or sodium-potassium alloy. Calcium hydride is widely used as a desiccant for

basic Basic or BASIC may refer to: Science and technology * BASIC, a computer programming language * Basic (chemistry), having the properties of a base * Basic access authentication, in HTTP Entertainment * Basic (film), ''Basic'' (film), a 2003 film ...

solvents such as

amine In chemistry, amines (, ) are organic compounds that contain carbon-nitrogen bonds. Amines are formed when one or more hydrogen atoms in ammonia are replaced by alkyl or aryl groups. The nitrogen atom in an amine possesses a lone pair of elec ...

s and pyridine. It is also used to dry alcohols. Despite its convenience, has a few drawbacks: *It is insoluble in all solvents with which it does not react vigorously, in contrast to , thus the speed of its drying action can be slow. *Because and are almost indistinguishable in appearance, the quality of a sample of is not obvious visually.

History

During the

Battle of the Atlantic The Battle of the Atlantic, the longest continuous military campaign in World War II, ran from 1939 to the defeat of Nazi Germany in 1945, covering a major part of the naval history of World War II. At its core was the Allies of World War II, ...

, German submarines used calcium hydride as a

sonar decoy A sonar decoy is a device for decoying sonar. One may be released from a submarine or a surface vessel. A decoy acts as false targets for human operators and/or sonar-homing weapons such as acoustic torpedoes. Many count as a type of torpedo defenc ...

called bold.

Other calcium hydrides

Although the term calcium hydride almost always refers to CaH, a number of molecular hydrides of calcium are known. One example is (Ca(μ-H)(thf)( nacnac)).

References

{{Hydrides by group Metal hydrides Calcium compounds Desiccants Hydrogen storage