What is Calcium Hydride (CaH2)? - Properties & Uses

Updated by Reginald Davey 08/09/2022

The chemical formula for Calcium Hydride is CaH2.

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Introduction

Calcium hydride has the formula CaH2. A grey powder (in its pure form, white), this chemical compound, when exposed to water, undergoes a vigorous reaction. Calcium hydride possesses a salt-like structure, and thus is classed as a saline hydride. This alkaline earth hydride possesses a cotunnite crystalline structure. Two ionic bonds exist between the calcium and hydrogen ions.

Preparation

Calcium hydride is easily prepared at high temperatures of 300-400oC from its constituent elements by direct combination. One processing route used is a two-step reduction process wherein vacuum distillation is used to convert CaO to calcium metal. It is then heated in the presence of hydrogen to form CaH2. Metallic sodium can be used in the process.

Properties

The molecular mass of calcium hydride is 42.094 g.mol. Its melting point is 816oC, and its density is 1.9 g.cm-3. As mentioned, whilst being extremely stable it is highly reactive in water and also reacts with alcohols.

Reactivity and Safety Considerations

Due to its high reactivity when in contact with water, special safety considerations need to be implemented for handling calcium hydride. It is also highly explosive when it reacts with other compounds such as tetrahydrofuran, potassium perchlorate, chloride, bromate, and hypochlorite. Furthermore, it can become incandescent when mixed with silver fluoride.

Because of these reactivity issues, calcium hydride must be handled in an inert atmosphere. The material is also extremely dangerous for individuals handling it due to being an irritant and highly corrosive. Ingestion and inhalation can cause lung damage and respiratory inflammation. Skin contact can cause blisters and dermatitis, and eye contact can lead to potential corneal damage and even blindness.

Severe overexposure to calcium hydride can be fatal. The severity of medical conditions is dependent on exposure time. Proper PPE must be used by laboratory and industrial workers handling this substance. The material must be stored in cool, dry places away from ignition sources. Waste products should be disposed of safely, with decomposition using methanol being a recommended method.

Industrial Uses

There are several industrial uses for this material. It is commonly used as a desiccant as it is a mild drying agent compared to substances with higher reactivity, such as sodium-potassium alloys. It can be employed for drying basic solvents such as pyridine and amines.

It is also used in hydrogen production and has a history of use for this purpose which goes back to the 1940s when it was marketed as a product called Hydrolith. It is still used to produce pure hydrogen for purposes such as fuel cell research. It is also used to evaluate the moisture content of diesel.

A third use of this industrial chemical is as a reducing agent. It is commonly utilized in powder metallurgy to reduce oxides of substances such as vanadium, uranium, zirconium, tantalum, and niobium under temperatures of between 600 and 1000oC.

Disadvantages

Whilst calcium hydride is extremely useful for key chemical processes, there are some critical drawbacks to the material. A slow drying agent, it is unsuitable for solvents that do not react well with it. In its powder form, it is incompatible with many common solvents. It is also unsuitable for deoxygenated solvents as it cannot remove dissolved O2.

Finally, the features of calcium hydride and calcium hydroxide are remarkably similar, meaning that distinguishing between these two compounds is problematic.

Density

The density of Calcium Hydride is tabulated below.

Property Value
Density ( g.cm-3 ) 1.9

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Further Reading and More Information

Sharma, P & Middleton, R (1987) Sample preparation and production of negative ions of calcium hydride for 41Ca AMS Interactions with Materials and Atoms 9 (1-2) pp. 63-66 [online] sciencedirect.com. Available at:

https://doi.org/10.1016/0168-583X(87)90205-9

Rees, A (2022) Calcium hydride: Properties, Reactivity, Handling, and Uses [online] en.lifeder.com. Available at:

https://en.lifeder.com/calcium-hydride/

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