Calcium hydride

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]

Calcium hydride
Calcium hydride
Names
IUPAC name
Calcium hydride
Other names
Calcium(II) hydride
Calcium dihydride
Hydrolith
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.029.263
EC Number 232-189-2
Properties
CaH2
Molar mass 42.094 g/mol
Appearance gray powder (white when pure)
Density 1.70 g/cm3, solid
Melting point 816 °C (1,501 °F; 1,089 K)
reacts violently
Solubility reacts in alcohol
Structure
Orthorhombic, oP12
Pnma, No. 62
Thermochemistry
41.4 J·mol−1·K−1[1]
−181.5 kJ·mol−1
-142.5 kJ/mol
Hazards
GHS pictograms The exclamation-mark pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS)The corrosion pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS)Water-react. 1The environment pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS)
GHS signal word DANGER
H260
NFPA 704
Flammability code 3: Liquids and solids that can be ignited under almost all ambient temperature conditions. Flash point between 23 and 38 °C (73 and 100 °F). E.g., gasolineHealth code 3: Short exposure could cause serious temporary or residual injury. E.g., chlorine gasReactivity code 2: Undergoes violent chemical change at elevated temperatures and pressures, reacts violently with water, or may form explosive mixtures with water. E.g., phosphorusSpecial hazard W: Reacts with water in an unusual or dangerous manner. E.g., cesium, sodiumNFPA 704 four-colored diamond
3
3
2
Related compounds
Other cations
Sodium hydride,
Potassium hydride
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

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]

See also

References

  1. ^ Zumdahl, Steven S. (2009). Chemical Principles 6th Ed. Houghton Mifflin Company. p. A21. ISBN 978-0-618-94690-7.
  2. ^ a b Gawley, R. E., Davis, A., "Calcium Hydride," in Encyclopedia of Reagents for Organic Synthesis, 2001, John Wiley & Sons, Ltd. doi:10.1002/047084289X.rc005
  3. ^ Wells, A.F. (1984) Structural Inorganic Chemistry, Oxford: Clarendon Press. ISBN 0-19-855370-6.
  4. ^ a b c Peter Rittmeyer, Ulrich Wietelmann “Hydrides” in Ullmann's Encyclopedia of Industrial Chemistry 2002, Wiley-VCH, Weinheim. doi:10.1002/14356007.a13_199
  5. ^ Hydrolith in thefreedictionary.com
  6. ^ Adlam G.H.J. and Price L.S., A Higher School Certificate Inorganic Chemistry, John Murray, London, 1940
  7. ^ 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
  8. ^ McNeil, Ian (2002-06-01). An Encyclopedia of the History of Technology. ISBN 9781134981649.
9 Ceti

9 Ceti is the Flamsteed designation for a star in the equatorial constellation of Cetus. It has an apparent visual magnitude of 6.39, which is below the limit that can be seen with the naked eye by a typical observer. (According to the Bortle scale, it is possible for some observers to see it from dark rural skies.) Based upon measurements made by the Hipparcos spacecraft, this star is around 68 light years away from the Sun. There is a magnitude 12.57 optical companion at an angular separation of 214 arc seconds along a position angle of 294° (as of 1999), although the pair are not physically associated as they have different proper motions.This is a solar analog, which is defined as a "Population I dwarf with gross properties not very different from those of the Sun". It is a G-type main sequence star with a stellar classification of G3 V, which means it is generating energy through the fusion of hydrogen into helium at its core. The mass and radius of the star are similar to the Sun, although the abundance of elements other than hydrogen and helium is about 50% greater. It is much younger than the Sun, being an estimated 850 million years of age. The effective temperature of the stellar atmosphere is around 5,807 K, giving it the yellow-hued glow of a G-type star.In 1980, this was found to be a variable star with a periodicity of 7.655 days, and it was given variable star designation BE Cet. This variation in luminosity was interpreted to be the result of rotational modulation of star spot activity in the photosphere, and hence it is classified as a BY Draconis variable. There is considerable variation in the strength of the surface activity—to the point where it has appeared inactive during some observation runs. The strength of the surface magnetic field was measured to be 450 G. The spectrum of this star includes lines of titanium oxide and calcium hydride, which, for a star of this class, is further evidence of star spot activity. Star spots cover an estimated 3% of the surface.This star has been examined for evidence of a planetary companion or a debris disk, but as of 2015 none has been found. The age of the star and its motion through space suggest that it is a member of the Hyades stellar kinematic group.

Ames Project

The Ames Project was a research and development project that was part of the larger Manhattan Project to build the first atomic bombs during World War II. It was founded by Frank Spedding from Iowa State College in Ames, Iowa as an offshoot of the Metallurgical Laboratory at the University of Chicago devoted to chemistry and metallurgy, but became a separate project in its own right. The Ames Project developed the Ames Process, a method for preparing pure uranium metal that the Manhattan Project needed for its atomic bombs and nuclear reactors. Between 1942 and 1945, it produced over 1,000 short tons (910 t) of uranium metal. It also developed methods of preparing and casting thorium, cerium and beryllium. In October 1945 Iowa State College received the Army-Navy "E" Award for Excellence in Production, an award usually only given to industrial organizations. In 1947 it became the Ames Laboratory, a national laboratory under the Atomic Energy Commission.

Barium hydride

Barium hydride is a chemical compound with the chemical formula Ba(H)2.

Beryllium hydride

Beryllium hydride (systematically named poly[beryllane(2)] and beryllium dihydride) is an inorganic compound with the chemical formula (BeH2)n (also written ([BeH2])n or BeH2). This alkaline earth hydride is a colourless solid that is insoluble in solvents that do not decompose it. Unlike the ionically bonded hydrides of the heavier Group 2 elements, beryllium hydride is covalently bonded (three-center two-electron bond).

Bold (decoy)

Bold (a term derived from kobold) was a German sonar decoy, used by U-boats during the Second World War from 1942 onwards. It consisted of a metal canister about 10 cm (3.9 in) in diameter filled with calcium hydride. It was launched by an ejector system colloquially referred to as Pillenwerfer (English: "pill thrower").

When mixed with seawater, the calcium hydride produced large quantities of hydrogen which bubbled out of the container, creating a false sonar target. A valve opened and closed, holding the device at a depth of about 30 m (98 ft). The device lasted 20 to 25 minutes.

The Royal Navy called it SBT (Submarine Bubble Target).

Calcium monohydride

Calcium monohydride is a molecule composed of calcium and hydrogen with formula CaH. It can be found in stars as a gas formed when calcium atoms are present with hydrogen atoms.

Hydride

In chemistry, a hydride is the anion of hydrogen, H−, or, more commonly, it is a compound in which one or more hydrogen centres have nucleophilic, reducing, or basic properties in it. In compounds that are regarded as hydrides, the hydrogen atom is bonded to a more electropositive element or groups. Compounds containing hydrogen bonded to metals or metalloid may also be referred to as hydrides. Common examples are ammonia (NH3), methane (CH4), ethane (C2H6) (or any other hydrocarbon), and Nickel hydride (NiH), used in NiMH rechargeable batteries.

Almost all of the elements form binary compounds with hydrogen, the exceptions being He, Ne, Ar, Kr, Pm, Os, Ir, Rn, Fr, and Ra.

Hydrolith

Hydrolith may refer to:

the philosopher's stone

a trade name for calcium hydride

a technique used in immersion lithography

Intramolecular reactions of diazocarbonyl compounds

Intramolecular reactions of diazocarbonyl compounds include addition to carbon–carbon double bonds to form fused cyclopropanes and insertion into carbon–hydrogen bonds or carbon–carbon bonds.

List of UN numbers 1401 to 1500

The UN numbers from UN1401 to UN1500 as assigned by the United Nations Committee of Experts on the Transport of Dangerous Goods.

Magnesium hydride

Magnesium hydride is the chemical compound with the molecular formula MgH2. It contains 7.66% by weight of hydrogen and has been studied as a potential hydrogen storage medium.

N,N-Diisopropylethylamine

N,N-Diisopropylethylamine, or Hünig's base, is an organic compound and an amine. It is named after the German chemist Siegfried Hünig. It is used in organic chemistry as a base. It is commonly abbreviated as DIPEA, DIEA, or i-Pr2NEt.

Petroleum ether

Petroleum ether is the petroleum fraction consisting of aliphatic hydrocarbons and boiling in the range 35‒60 °C; commonly used as a laboratory solvent. Despite the name, petroleum ether is not classified as an ether; the term is used only figuratively, signifying extreme lightness and volatility.

Sonar decoy

A sonar decoy is a device for decoying sonar. Most are released from submarines to act as a false target.

Standard Gibbs free energy of formation

The standard Gibbs free energy of formation of a compound is the change of Gibbs free energy that accompanies the formation of 1 mole of a substance in its standard state from its constituent elements in their standard states (the most stable form of the element at 1 bar of pressure and the specified temperature, usually 298.15 K or 25 °C).

The table below lists the Standard Gibbs function of formation for several elements and chemical compounds and is taken from Lange's Handbook of Chemistry. Note that all values are in kJ/mol. Far more extensive tables can be found in the CRC Handbook of Chemistry and Physics and the NIST JANAF tables. The NIST Chemistry WebBook (see link below) is an online resource that contains standard enthalpy of formation for various compounds along with the standard absolute entropy for these compounds from which the Standard Gibbs Free Energy of Formation can be calculated.

Standard enthalpy of formation

The standard enthalpy of formation or standard heat of formation of a compound is the change of enthalpy during the formation of 1 mole of the substance from its constituent elements, with all substances in their standard states. The standard pressure value p⦵ = 105 Pa (= 100 kPa = 1 bar) is recommended by IUPAC, although prior to 1982 the value 1.00 atm (101.325 kPa) was used. There is no standard temperature. Its symbol is ΔfH⦵. The superscript Plimsoll on this symbol indicates that the process has occurred under standard conditions at the specified temperature (usually 25 °C or 298.15 K). Standard states are as follows:

For a gas: the hypothetical state it would have assuming it obeyed the ideal gas equation at a pressure of 1 bar

For a solute present in an ideal solution: a concentration of exactly one mole per liter (1 M) at a pressure of 1 bar

For a pure substance or a solvent in a condensed state (a liquid or a solid): the standard state is the pure liquid or solid under a pressure of 1 bar

For an element: the form in which the element is most stable under 1 bar of pressure. One exception is phosphorus, for which the most stable form at 1 bar is black phosphorus, but white phosphorus is chosen as the standard reference state for zero enthalpy of formation.For example, the standard enthalpy of formation of carbon dioxide would be the enthalpy of the following reaction under the above conditions:

C(s, graphite) + O2(g) → CO2(g)All elements are written in their standard states, and one mole of product is formed. This is true for all enthalpies of formation.

The standard enthalpy of formation is measured in units of energy per amount of substance, usually stated in kilojoule per mole (kJ mol−1), but also in kilocalorie per mole, joule per mole or kilocalorie per gram (any combination of these units conforming to the energy per mass or amount guideline).

All elements in their standard states (oxygen gas, solid carbon in the form of graphite, etc.) have a standard enthalpy of formation of zero, as there is no change involved in their formation.

The formation reaction is a constant pressure and constant temperature process. Since the pressure of the standard formation reaction is fixed at 1 bar, the standard formation enthalpy or reaction heat is a function of temperature. For tabulation purposes, standard formation enthalpies are all given at a single temperature: 298 K, represented by the symbol ΔfH⦵298 K.

Tert-Butyl alcohol

tert-Butyl alcohol (TBA), also called tert-butanol or t-butanol, is the simplest tertiary alcohol, with a formula of (CH3)3COH (sometimes represented as t-BuOH). It is one of the four isomers of butanol. tert-Butyl alcohol is a colorless solid, which melts near room temperature and has a camphor-like odor. It is miscible with water, ethanol and diethyl ether.

Triethylamine

Triethylamine is the chemical compound with the formula N(CH2CH3)3, commonly abbreviated Et3N. It is also abbreviated TEA, yet this abbreviation must be used carefully to avoid confusion with triethanolamine or tetraethylammonium, for which TEA is also a common abbreviation. It is a colourless volatile liquid with a strong fishy odor reminiscent of ammonia and is also the smell of the hawthorn plant. Like diisopropylethylamine (Hünig’s base), triethylamine is commonly employed in organic synthesis.

Triphenylmethane

Triphenylmethane, or triphenyl methane, is the hydrocarbon with the formula (C6H5)3CH. This colorless solid is soluble in nonpolar organic solvents and not in water. Triphenylmethane is the basic skeleton of many synthetic dyes called triarylmethane dyes, many of them are pH indicators, and some display fluorescence. A trityl group in organic chemistry is a triphenylmethyl group Ph3C, e.g. triphenylmethyl chloride (trityl chloride) and the triphenylmethyl radical (trityl radical).

Calcium compounds
Alkali metal hydrides
Alkaline earth hydrides
Group 13 hydrides
Group 14 hydrides
Pnictogen hydrides
Hydrogen chalcogenides
Hydrogen halides
Transition metal hydrides
Lanthanide hydrides
Actinide hydrides

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