Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references
Calcium hydride is the chemical compound with the formula CaH2, and is therefore an alkaline earth hydride. This grey powder (white if pure, which is rare) reacts vigorously with water liberating hydrogen gas. CaH2 is thus used as a drying agent, i.e. a desiccant.[2]
CaH2 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. CaH2 crystallizes in the PbCl2 (cotunnite) structure.[3]
Contents
1Preparation
2Uses
2.1Reduction of metal oxides
2.2Hydrogen source
2.3Desiccant
2.4Sonar decoy
3See also
4References
Preparation
Calcium hydride is prepared from its elements by direct combination of calcium and hydrogen at 300 to 400 °C.[4]
Uses
Reduction of metal oxides
CaH2 is a reducing agent for the production of metal powders from the oxides of Ti, V, Nb, Ta, and U. It is proposed to operate via its decomposition to Ca metal:[4]
TiO2 + 2 CaH2 → Ti + 2 CaO + 2 H2
Hydrogen source
CaH2 has been used for hydrogen production. In the 1940s, it was available under the trade name "Hydrolith"[5] 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.'[6]
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 CaH2.[4]
Desiccant
The reaction of CaH2 with water can be represented as follows:
CaH2 + 2 H2O → Ca(OH)2 + 2 H2
The two hydrolysis products, gaseous H2 and Ca(OH)2, are readily separated from the dried solvent.
Calcium hydride is a relatively mild desiccant and, compared to molecular sieves, probably inefficient.[7] Its use is safer than more reactive agents such as sodium metal or sodium-potassium alloy. Calcium hydride is widely used as a desiccant for basic solvents such as amines and pyridine. It is also used to dry alcohols.[2]
Despite its convenience, CaH2 has a few drawbacks:
It is insoluble in all solvents with which it does not react vigorously, in contrast to LiAlH4, thus the speed of its drying action can be slow.
Because CaH2 and Ca(OH)2 are almost indistinguishable in appearance, the quality of a sample of CaH2 is not obvious visually.
Sonar decoy
During the Battle of the Atlantic, German submarines used calcium hydride as a sonar decoy called bold.[8]
^ abGawley, R. E., Davis, A., "Calcium Hydride," in Encyclopedia of Reagents for Organic Synthesis, 2001, John Wiley & Sons, Ltd. doi:10.1002/047084289X.rc005
^ abcPeter Rittmeyer, Ulrich Wietelmann “Hydrides” in Ullmann's Encyclopedia of Industrial Chemistry 2002, Wiley-VCH, Weinheim. doi:10.1002/14356007.a13_199
^Hydrolith in thefreedictionary.com
^Adlam G.H.J. and Price L.S., A Higher School Certificate Inorganic Chemistry, John Murray, London, 1940
^Williams, D. B. G., Lawton, M., "Drying of Organic Solvents: Quantitative Evaluation of the Efficiency of Several Desiccants", The Journal of Organic Chemistry 2010, vol. 75, 8351. doi: 10.1021/jo101589h
^McNeil, Ian (2002-06-01). An Encyclopedia of the History of Technology. ISBN 9781134981649.
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Calcium compounds
CaAl2O4
CaB6
CaBr2
Ca(BrO3)2
CaC2
CaCN2
Ca(CN)2
CaCO3
CaC2O4
CaCl2
Ca(ClO)2
Ca(ClO3)2
CaCrO4
CaF2
CaH2
Ca(HCO3)2
CaH2S2O6
CaI2
Ca(IO3)2
Ca(MnO4)2
CaN6
Ca(NO3)2
CaO
CaO2
Ca(OH)2
CaP
CaS
CaSO3
CaSO4
CaSe
CaSi
CaSi2
CaTiO3
Ca2P2O7
Ca2SiO4
Ca3Al2O6
Ca3(AsO4)2
Ca3(BO3)2
Ca3(C6H5O7)2
Ca3N2
Ca3P2
Ca4(PO4)2O
Ca3(PO4)2
Ca(H2PO4)2
CaHPO4
C36H70CaO4
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Binary compounds of hydrogen
Alkali metal hydrides
LiH
NaH
KH
RbH
CsH
Lithium hydride, LiH ionic metal hydride
Beryllium hydride Left (gas phase): BeH2 covalent metal hydride Right: (BeH2)n (solid phase) polymeric metal hydride
Clash Royale CLAN TAG #URR8PPP A coarse-grained mafic intrusive rock Gabbro Photomicrograph of a thin section of gabbro Gabbro ( / ˈ ɡ æ b r oʊ / ) is a phaneritic (coarse-grained), mafic intrusive igneous rock formed from the slow cooling of magnesium-rich and iron-rich magma into a holocrystalline mass deep beneath the Earth's surface. Slow-cooling, coarse-grained gabbro is chemically equivalent to rapid-cooling, fine-grained basalt. Much of the Earth's oceanic crust is made of gabbro, formed at mid-ocean ridges. Gabbro is also found as plutons associated with continental volcanism. Due to its variant nature, the term "gabbro" may be applied loosely to a wide range of intrusive rocks, many of which are merely "gabbroic". Contents 1 Etymology 2 Petrology 3 Distribution 4 Uses 5 See also 6 References 7 External links Etymology The term "gabbro" was used in the 1760s to name a set of rock types that were found in the ophiolites of the Apenn
Clash Royale CLAN TAG#URR8PPP
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