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Category: Hydrogen Products

Hydrogen, consisting of one proton and one electron, is the most basic and abundant element in the universe and the third most abundant (next to oxygen and silicon) on planet Earth. In fact, about 15% of all atoms on Earth are hydrogen atoms. Hydrogen is the lightest element, though accounts for roughly 90% of the universe by weight. Hydrogen is a Block S, Group 1, Period 1 element. The number of electrons in each of Hydrogen’s shells is 1 and its electronic configuration is 1s1.

Arsine

Arsine is flammable and highly toxic gas with formula AsH3. It is one of the simpler compounds of Arsenic. Reaction of arsenic-containing substances with newly formed hydrogen in water or acids leads to formation of Arsine gas. Although Arsine is odorless, it is possible to smell like mild garlic when it is present at above about 0.5 ppm

Other names for Arsine

Arsine is known by many other names like

  • Arsenic Hydride
  • Hydrogen Arsenide
  • Arseniuretted Hydrogen
  • Arsenious Hydride
  • Arsenic Trihydride

Chemical definition of Arsine

Arsines refers to a group of organoarsenic compounds of the formula AsH3−xRx, where R denotes aryl or alkyl. For instance, As(C6H5)3 that is known as Triphenylarsine is an Arsine.

Molecule of Arsine

Commercial availability of Arsine

It is generally commercially available as a liquefied compressed gas in cylinders.

Properties of Arsine

Some of the main properties of Arsine are

  • It is colorless
  • It is odorless, but smells like mild garlic when present at above about 0.5 ppm
  • It is slightly soluble in water (20% at 20º C)
  • It has a molecular weight of 78.0 daltons
  • It has a boiling point (760 mm Hg) of  -62.5ºC.
  • It is denser than air with gas density of 2.7 (air = 1)
  • It is extremely flammable and may be ignited by heat, sparks, or flames.
  • It is a stable compound and decomposes only gradually at room temperature. Humidity, presence of light and specific catalysts (namely aluminum) is some of the factors that determine its rate of decomposition.
  • It can react dangerously with halogens like fluorine and chlorine or some of their compounds, resulting in explosions
  • It reacts violently with strong oxidizing agents such as potassium permanganate and nitric acid
  • As is common with heavy hydrides such as SbH3, H2Te and SnH4, it is unstable thermodynamically though stable kinetically
  • It can be oxidized with concentrated O2 or dilute O2 concentration. This is a relatively simple process that can be represented by the chemical formula:             2 AsH3 + 3 O2 → As2O3 + 3 H2O
  • Unlike PH3, this substance does not form stable chains, although H2As–AsH2 and even H2As–As(H)–AsH2 have been spotted. Diarsine is unstable above −100 °C.
  • Although usually regarded as non-basic, isolable salts of the tetrahedral groups [AsH4] + can be produced by pronation of arsines by superacids.

Uses and applications of Arsine

This substance has varied uses.

  • It finds its use in the semiconductor industry as a dopant. For silicon and germanium, arsenic is an n-dopant in relation to P. More importantly, Arsine is deployed at 700–900 °C to manufacture the semiconductor GaAs by chemical vapor deposition (CVD): Ga(CH3)3 + AsH3 → GaAs + 3 CH4
  • Acidic properties of As–H bond are often harnessed. Thus, arsine can be deprotonated: AsH3 + NaNH2 → NaAsH2 + NH3
  • The use of arsine was suggested in chemical warfare because of arsine gas being colorless, almost odorless, and 2.5 times denser than air, ideal for a blanketing effect. Despite such favorable traits, arsine was never formally used as a weapon, due to its high flammability and its reduced efficacy in comparison to non-flammable substitute phosgene.
  • It is sometimes used in soldering, galvanizing, burnishing, and lead plating.

Health effects of exposure to Arsine

Exposure to Arsine majorly occurs through inhalation. It is non-irritating and creates no urgent warning signs. Symptoms like nausea, dizziness and abdominal pain may be experienced within few hours of contact with 3 ppm of Arsine. Exposure to large dose of Arsine may lead to additional health implications including convulsions, paralysis, and respiratory failure. Skin contact with liquid Arsine can lead to frostbite. Severe exposure to Arsine is fatal in most cases. Those who survive may have long-term effects including

  • Kidney damage
  • Numbness
  • Pain in extremities
  • Neurological problems such as loss of memory, confusion and irritation

Treatment for exposure to Arsine

Blood transfusions and IV (intravenous) fluids may be required. Hemodialysis may be needed in case of some patients.

Precautions for exposure to Arsine

As no antidote to Arsine exists, the best precaution is to avoid it. However, if exposed, one needs to move immediately to an area of fresh air to reduce serious implications. You are advised to change your cloth and wash yourself thoroughly if you think that you are exposed to Arsine.

References:

http://www.atsdr.cdc.gov/mhmi/mmg169.html

http://www.bt.cdc.gov/agent/arsine/facts.asp

http://www.epa.gov/iris/subst/0672.htm

http://www.hpa.org.uk/Topics/ChemicalsAndPoisons/CompendiumOfChemicalHazards/Arsine/

Calcium Hydride

Calcium Hydride is a chemical compound mainly used as a desiccant or a drying agent. This grey powder reacts with water and releases hydrogen gas. All alkali metals and alkaline earth metals form saline hydrides. Calcium Hydride is an example of saline hydride crystallizing in the lead chloride (PbCl2) motif.

Identification of Calcium Hydride

CAS number: 7789-78-8

PubChem: 105052

ChemSpider: 94784

EC number: 232-189-2

Calcium Hydride Preparation

This chemical compound can be produced by reacting calcium and hydrogen in a temperature between 300 and 400°C. Another way to prepare Calcium Hydride is to heat calcium chloride along with hydrogen and sodium metal. The reaction happens in the following way:

Calcium Hydride Picture


Picture 1 – Calcium Hydride

CaCl2 + H2 + 2 Na → CaH2 + 2 NaCl

In this reaction the calcium (Ca) and hydrogen (H) create a Calcium Hydride molecule while the sodium atoms create sodium chloride molecules along with chlorine.

Calcium Hydride can also be produced by reducing calcium oxide (CaO) with magnesium (Mg). The reaction is done in the presence of hydrogen. This reaction also produces magnesium oxide. Following is the formula for this chemical reaction:

CaO + Mg + H2 → CaH2 + MgO

Formula of Calcium Hydride

The formula for this chemical compound is CaH2.

Properties of Calcium Hydride

Here are some of the basic physical and chemical properties of this compound:

Appearance: This compound is white in its pure form; however, it usually appears as grey powder.

Odor: It is odorless.

Solubility: This powder reacts violently with water to produce hydrogen. It also reacts in alcohol.

Molar Mass: The molars mass of this material is 42.094 g/mol.

Specific Gravity: Its specific gravity is 1.9.

Melting Point: It has a melting point of 816 °C.

Density: Its density is 1.70 g/ cm3.

Uses of Calcium Hydride

There are two main uses of this compound: one is as a desiccant while the other is for producing hydrogen.

Use of Calcium Hydride as a desiccant

It is a relatively mild desiccant. Due to this reason, using this compound as a desiccant is safer compared more reactive agents like sodium-potassium alloys and sodium metal.  It reacts with water in the following way:

CaH2 + 2 H2O → Ca(OH)2 + 2 H2

The hydrolysis products of this reaction  ̶  hydrogen (gas) and Ca(OH)(an aqueous mixture)  ̶  can be separated from the chemical solvent following the process of filtration, distillation or decantation.

This chemical compound is an efficient desiccant for many basic solvents like amines and pyridine. It is sometimes used for pre-drying solvents before using more reactive desiccants.

Use of Calcium Hydride for Hydrogen Production

In the 1940s, this compound was available as a hydrogen source under the trade-name of “Hydrolith”. It has been used as a source of hydrogen for a very long time. It is still used for producing pure hydrogen in laboratories for various experiments.

Apart from these two uses, this powdered compound is also used as a strong reducing agent.

Disadvantages of using Calcium Hydride

This chemical compound is often the preferred choice for drying agent; however, it also has some disadvantages:

  • The drying action of this compound is slow as it is not soluble in any solvent with which it does not react violently.
  • This powdered compound is incompatible with many solvents. Its reaction with chlorocarbons can even result in explosions.
  • It cannot be used for deoxygenating solvents as it is unable to remove dissolved oxygen.
  • Differentiating between Calcium Hydride and Calcium hydroxide is quite difficult because of their similar appearances.

Material Safety Data Sheet (MSDS)s of Calcium Hydride

This material is not inflammable. However, this powder can cause serious health hazards for humans if comes to direct contact.

Toxicology

It can cause severe irritation in case of direct contact with eyes and skin. Accidental inhalation and ingestion may also cause hazardous effects on human health.

First Aid Measures

Eye Contact: The victim should immediately remove any contact lenses and flush the eyes with plenty of water at least for 15 minutes. Immediate medical assistance is required.

Skin Contact: One should immediately wash the affected skin area with a disinfectant soap and lots of water and apply an anti-bacterial cream. The contaminated clothes and shoes should be removed and washed properly before re-use. It is important to seek immediate medical aid.

Inhalation: The victim should be removed to a well ventilated area. Oxygen and artificial respiration should be provided in case the victim is experiencing breathing difficulty. One should immediately seek medical attention.

Ingestion: It is not advisable to induce vomiting without proper medical direction in case of accidental ingestion. Any tight clothing like tie, belt and waistband should be loosened or removed. Getting immediate medical assistance is important.

Personal Safety Measure

Using NIOSH approved splash goggles, protective gloves, synthetic apron and dust respirators is important for proper personal protection.

Fire Fighting Measures

It is a non-flammable material. However, fire fighters should use proper fire fighting gear while extinguishing a fire around this chemical compound. It is never advisable to use water to extinguish a fire around Calcium Hydride as it will react violently with water producing hydrogen gas. Dry sand as well as compounds like sodium chloride and sodium carbonate can be used for this purpose.

Availability of Calcium Hydride

There are numerous companies all over the world who supply this material. It is also available online at reasonable prices.

Calcium Hydride is highly useful in various industries as desiccant. It is counted among the most important hydrogen sources used for industrial and experimental purposes.

References:

http://www.espimetals.com/index.php/msds/478-calcium-hydride

http://www.sciencelab.com/msds.php?msdsId=9927122

http://chemicalland21.com/industrialchem/IUH/CALCIUM%20HYDRIDE.htm

https://ecat.fishersci.ca/%28S%28chq3ba45gaqnnd45w1icsbzn%29%29/ViewMSDS.aspx?cat=C94100

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