CALCIUM HYDRIDE (CAH2): PROPERTIES, REACTIVITY AND USES - CHEMISTRY - 2025

The calcium hydride is a chemical compound of formula CaH2, which makes alkaline earth hydride. This chemical compound has two ionic bonds between calcium and the two hydride ions, as shown in Figure 1.

It is a saline hydride, which means that its structure is similar to salt. Its crystalline structure is the same as that of lead chloride (cotunnite mineral) as shown in figure 2.

Figure 1: structure of calcium hydride

Figure 2: crystal structure of calcium hydride

All alkali and alkaline earth metals form hydride salts. In chemistry, a hydride is the anion of hydrogen, H- or, more commonly, it is a compound in which one or more hydrogen centers have nucleophilic, reducing or basic properties.

In compounds that are considered hydrides, the hydrogen atom is attached to a more electropositive element or group.

It can be produced by reacting calcium and hydrogen at a temperature between 300 and 400 degrees Celsius. Another way to prepare calcium hydride is to heat calcium chloride together with hydrogen and metallic sodium. The reaction happens as follows:

CaCl2 + H2 + 2Na → CaH2 + 2NaCl

In this reaction, calcium (Ca) and hydrogen (H) create a molecule of calcium hydride while sodium atoms together with chlorine create molecules of sodium chloride (NaCl).

Calcium hydride can also be produced by reducing calcium oxide (CaO) with magnesium (Mg). The reaction is carried out in the presence of hydrogen. This reaction also produces magnesium oxide (MgO). Below is the formula for this chemical reaction:

CaO + Mg + H2 → CaH2 + MgO

Physical and chemical properties of calcium hydride

Calcium hydride is a set of crystals with an orthorhombic structure that are white when pure. Generally, it is rare to find it in this form so it tends to have a grayish hue. It lacks a characteristic odor. Its appearance is shown in figure 3 (Royal Society of Chemistry, 2015).

Figure 3: appearance of calcium hydride

It has a molecular weight of 42.094 g / mol, has a melting point of 816 degrees centigrade and a density of 1.70 g / ml. If it dissolves in water, it reacts violently, producing hydrogen. It also reacts with alcohol (National Center for Biotechnology Information., SF).

Reactivity and hazards

Calcium hydride is a stable chemical, although it is highly reactive to water or moisture. In contact with water, it releases flammable hydrogen gases that can ignite spontaneously.

It is considered an explosive compound. When heated in a reaction with tetrahydrofuran, it can cause an explosion. When mixed with chlorate, hypochlorite, bromate, potassium perchlorate, it becomes sensitive to heat, friction, and becomes explosive (Calcium Hydride 7789-78-8, 2016).

When silver fluoride is crushed with calcium hydride, the mass becomes incandescent. Strong heating of the hydride with chlorine, bromine or iodine leads to incandescence.

Mixtures of the hydride with various bromates, for example barium bromate or chlorates, for example barium chlorate and perchlorates such as potassium perchlorate, explode on grinding. CaH2 reacts incandescently with silver fluoride if it is subject to friction.

This compound must be handled under an inert atmosphere. If not handled properly, it can pose a serious threat to the health and safety of laboratory personnel, first responders, and chemical waste handlers (UC center for laboratory safety, 2013).

Extremely dangerous in case of contact with the skin or eyes, as it is an irritant. Very dangerous in case of contact with the skin as it can be corrosive.

It is also dangerous in case of ingestion and inhalation. The amount of tissue damage depends on the length of the contact. Contact with the eyes can result in corneal damage or blindness.

Contact with the skin can cause inflammation and blisters. Inhalation of dust will produce irritation of the gastrointestinal or respiratory tract, characterized by burning, sneezing and coughing.

Severe overexposure can cause lung damage, suffocation, unconsciousness, and even death. Inflammation of the eye is characterized by redness, watering, and itching. Inflammation of the skin is characterized by itching, peeling, redness, or occasionally blistering.

Repeated low level eye exposure may cause eye irritation. Repeated skin exposure can cause local skin destruction, or dermatitis.

Repeated inhalation of dust can produce varying degrees of respiratory irritation or lung damage. Repeated or prolonged inhalation of dust can cause chronic respiratory irritation (Material Safety Data Sheet Calcium hydride MSDS, 2005).

In case of contact with the eyes, they should be rinsed immediately with plenty of water for at least 15 minutes, occasionally lifting the upper and lower eyelids.

In case of contact with the skin, rinse immediately with plenty of water for at least 15 minutes while removing contaminated clothing and shoes.

In case of ingestion, vomiting should not be induced. A poison control center should be called. It is advisable to leave the place of exposure and move outdoors immediately.

In case of inhalation, if breathing is difficult it is necessary to supply oxygen. Mouth-to-mouth resuscitation should not be given if the victim has swallowed or inhaled the substance.

Artificial respiration should be induced with the aid of a pocket mask fitted with a one-way valve or other suitable respiratory medical device. In all cases, medical attention should be obtained immediately.

Handling and storage

The compound should be kept in a dry container away from heat. It should be kept away from sources of ignition. Dust should not be breathed. Water should not be added to this product

In case of insufficient ventilation, wear suitable respiratory equipment such as a filter mask. In the event of exposure, seek medical attention and display the label where possible. Avoid contact with skin and eyes.

Flammable materials, in general, should be stored in a separate security closet or storage room. Keep the container tightly closed.

Keep in a cool and well-ventilated place. All equipment containing material must be grounded to avoid electrical sparks. The container should be kept dry and in a cool place.

It is a non-flammable material. However, firefighters must wear appropriate equipment while fighting a fire around this chemical compound.

It is never advisable to use water to extinguish a fire around calcium hydride. Dry sand, as well as compounds such as sodium chloride and sodium carbonate can be used for this purpose.

To remove calcium hydride debris, it must be decomposed by adding 25 ml of methanol for each gram of hydride under a nitrogen atmosphere while stirring.

After the reaction is complete, the same volume of water is added to the aqueous calcium methoxide compound and discharged into the drain with plenty of water (national research council, 1995).

Uses and applications

Desiccant agent

Potassium hydride is a relatively mild desiccant. Due to this reason, the use of this compound as a desiccant is safer compared to more reactive agents, such as sodium-potassium and sodium metal alloys. Reacts with water as follows:

CaH2 + 2 H2O → Ca (OH) 2 + 2 H2

The hydrolysis products of this reaction, hydrogen (gas) and Ca (OH) 2 (an aqueous mixture), can be separated from the chemical solvent by following a process of filtration, distillation or decantation.

This chemical compound is an effective desiccant for many basic solvents such as amines and pyridine. It is sometimes used to pre-dry solvents before using more reactive desiccants.

Hydrogen production

In the 1940s, this compound was available as a source of hydrogen under the trade name "Hydrolith."

It has been used as a source of hydrogen for a long time. It is still used to produce pure hydrogen in laboratories for various experiments, advanced fuel cells, and battery applications (American Elements, SF).

The compound has been widely used for decades as a safe and convenient means of inflating weather balloons.

It is also regularly used in laboratories to produce small amounts of highly pure hydrogen for experiments. The moisture content of diesel fuel is calculated from the hydrogen developed after treatment with CaH2.

Reducing agent

When heated between 600 and 1000 degrees centigrade, zirconium oxide, niobium, uranium, chromium, titanium, vanadium and tantalum can be reduced to prepare the powder of these metals, so calcium hydride can be used in metallurgy of dust.

The following reaction illustrates how calcium hydride acts as a reducing agent:

TiO + 2CaH2 → CaO + H2 + Ti

Disadvantage in the use of calcium hydride

This chemical compound is often the preferred choice as a drying agent; However, it also has some disadvantages:

-The drying action of this compound is slow, since it is not soluble in any solvent with which it does not react violently.

-This powdered compound is incompatible with many solvents. Their reaction with chlorocarbons can even cause explosions.

-It cannot be used for deoxygenating solvents, as it is not capable of removing dissolved oxygen.

-Differentiating between calcium hydride and calcium hydroxide is quite difficult due to their similar appearances.

References

1. American Elements. (SF). calcium hydride. Retrieved from americanelements.com: americanelements.com.
2. Calcium Hydride 7789-78-8. (2016). Retrieved from chemicalbook.com: chemicalbook.com.
3. calcium hydride. (sf). Retrieved from chemistry learner: chemistrylearner.com.
4. Material Safety Data Sheet Calcium hydride MSDS. (2005, October 10). Retrieved from sciencelab.com: sciencelab.com.
5. National Center for Biotechnology Information. (SF). PubChem Compound Database; CID = 105052. Retrieved from pubchem.ncbi.nlm.nih.gov: pubchem.ncbi.nlm.nih.gov.
6. national research council. (nineteen ninety five). Prudent Practices in the Laboratory: Handling and Disposal of Chemicals. Washinton: NationalAacademy Press.
7. Royal Society of Chemistry. (2015). calcium hydride ID 94784. Retrieved from chemspider.com: chemspider.com.
8. UC center for laboratory safety. (2013, January 18). standard operating procedure calcium hydride. Retrieved from chemengr.ucsb.edu: chemengr.ucsb.edu.