He Calcium hydride Is a chemical compound of the formula CaH2, which makes it an alkaline earth metal hydride. This formula has a structure similar to salt.
This chemical compound has two Ionic bonds Between the calcium and the two hydride ions as shown in figure 1.
Figure 1: calcium hydride structure
As I said, CaH2 is a saline hydride, which means that its structure is similar to salt. Its crystal structure is the same as that of lead chloride (mineral cotunnite) as shown in figure 2.
Figure 2: crystal structure of calcium hydride
All the alkali metals And alkaline earth metals form hydride salts. In chemistry, a hydride is the anion Of hydrogen, H- or, more commonly, is a compound in which one or more hydrogen centers have nucleophilic, reducing or basic properties.
In compounds which 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 the calcium chloride together with hydrogen and sodium metal. The reaction takes place as follows:
CaCl2 + H2 + 2Na → CaH2 + 2NaCl
In this reaction calcium (Ca) and hydrogen (H) create a calcium hydride molecule while sodium atoms together with chlorine create sodium chloride (NaCl) molecules.
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). Here is the formula for this chemical reaction:
CaO + Mg + H2 → CaH2 + MgO
(Calcium hydride, s.f.)
Physical and chemical properties of calcium hydride
Calcium hydride is a set of crystals of white orthorhombic structure when it is pure. Generally, it is rare to find it in this form so it usually has a grayish tint. It lacks a distinctive odor. Their 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 Celsius 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., S.F.).
Reactivity and hazards
Calcium hydride is a stable chemical, although it is highly reactive to water or moisture. In contact with water, it releases inflammable gases of hydrogen that can ignite spontaneously.
It is considered an explosive compound. When heated in a reaction with Tetrahydrofuran , May 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 the silver fluoride is triturated with calcium hydride, the mass becomes incandescent. The 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, are exploited when grinding. CaH2 reacts incandescently with silver fluoride if subject to friction.
This compound should be handled under an inert atmosphere. If not handled properly, it can pose a serious threat to the health and safety of laboratory personnel, rescuers and chemical waste handlers (UC center for laboratory safety, 2013).
Extremely hazardous in case of contact with skin or eyes, as it is irritating. Very hazardous in case of skin contact as it may be corrosive.
It is also dangerous if swallowed and inhaled. The amount of tissue damage depends on the length of the contact. Contact with eyes may result in corneal damage or blindness.
Contact with skin may cause swelling and blisters. Inhalation of dust will produce irritation of the gastrointestinal or respiratory tract, characterized by burning, sneezing and coughing.
Severe overexposure may cause lung damage, asphyxia, 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 exposure of the eyes to a low level may cause irritation to the eyes. Repeated exposure to the skin may result in local skin destruction, or dermatitis.
Repeated inhalation of dust may produce a varying degree of respiratory irritation or lung damage. Repeated or prolonged inhalation of dust may cause chronic respiratory irritation (Material Safety Data Sheet Calcium hydride MSDS, 2005).
In case of contact with eyes, rinse immediately with plenty of water for at least 15 minutes, occasionally lifting the upper and lower eyelids.
In case of contact with skin, rinse immediately with plenty of water for at least 15 minutes while removing contaminated clothing and shoes.
In case of ingestion do not induce vomiting. Call a poison control center. 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. Do not give mouth-to-mouth breathing if the victim ingested or inhaled the substance.
Artificial respiration should be induced with the aid of a pocket mask equipped with a one-way valve or other suitable respiratory medical device. In all cases, medical attention should be sought immediately.
Handling and storage
The compound should be kept in a dry container away from heat. Keep away from sources of ignition. Do not breathe dust. Do not add water to this product
In case of insufficient ventilation, wear suitable respiratory equipment such as a filter mask. In case of exposure, seek medical attention and show the label as much as possible. Avoid contact with skin and eyes.
Flammable materials, in general, should be stored in a separate security cabinet or storage room. Keep the container tightly closed.
Keep in a cool, well-ventilated place. All equipment containing material to avoid electrical sparks should be grounded. The container should be kept dry and in a cool place.
It is a non-flammable material. However, firefighters should wear appropriate equipment while extinguishing a fire around this chemical.
It is never advisable to use water to extinguish a fire around the calcium hydride. Dry sand can be used as well as compounds such as sodium chloride and sodium carbonate for this purpose.
To remove calcium hydride debris, it must be decomposed by adding 25 ml of methanol per gram of hydride under a nitrogen atmosphere while stirring.
After completion of the reaction, the same volume of water is added to the aqueous calcium methoxide compound and discarded in the drain with water (National Research Council, 1995).
Uses and applications
1 - Desiccant agent
Potassium hydride is a relatively mild desiccant. Because of 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 following a filtration, distillation or decantation process.
This chemical 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.
2 - Production of hydrogen
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, S.F.).
The compound has been widely used for decades as a safe and convenient medium for inflating weather balloons.
It is also used regularly in laboratories to produce small quantities of highly pure hydrogen for experiments. The moisture content of the diesel fuel is calculated by the hydrogen developed after treatment with CaH2.
3 - 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 that 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 powder compound is incompatible with many solvents. Its reaction with chlorocarbons can even cause explosions.
- It can not be used for deoxygenating solvents as it is not able to remove dissolved oxygen.
- Differentiate between calcium hydride and calcium hydroxide Is quite difficult because of their similar appearances.
References
- American Elements. (S.F.). Calcium hydride. Retrieved from americanelements.com: americanelements.com.
- Calcium Hydride 7789-78-8. (2016). Retrieved from chemicalbook.com: chemicalbook.com.
- Calcium hydride. (S.f.). Retrieved from chemistry learner: chemistrylearner.com.
- Material Safety Data Sheet Calcium hydride MSDS. (2005, October 10). Retrieved from sciencelab.com: sciencelab.com.
- National Center for Biotechnology Information. (S.F.). PubChem Compound Database; CID = 105052. Retrieved from pubchem.ncbi.nlm.nih.gov: pubchem.ncbi.nlm.nih.gov.
- National research council. (nineteen ninety five). Prudent Practices in the Laboratory: Handling and Disposal of Chemicals. Washington: National academy Press.
- Royal Society of Chemistry. (2015). Calcium hydride ID 94784. Retrieved from chemspider.com: chemspider.com.
- UC center for laboratory safety. (2013, January 18). Standar operatin procedure calcium hydride. Retrieved from chemengr.ucsb.edu: chemengr.ucsb.edu.