General Description
Grayish-colored lump or crystalline solid. Irritating to skin and eyes. Used to make other chemicals.
Reactivity Profile
When silver fluoride is ground with CALCIUM HYDRIDE(7789-78-8) the mass becomes incandescent [Mellor 3:389 1946-47]. Heating the hydride strongly with chlorine, bromine, or iodine leads to incandescence. Mixtures of the hydride with various bromates, i.e. barium bromate; chlorates, i.e. barium chlorate, and perchlorates, i.e. potassium perchlorate; explode on grinding, [Mellor, 1946, vol. 3, 651]. CaH2 reacts incandescently with AgF if subject to friction. (Mellor, 1941, Vol. 3, 389, 651).
Air & Water Reactions
Ignites in air or reacts violently, sometimes explosively, with air of high humidity [Bretherick 1979 p. 107]. Reacts exothermically with water to generate flammable hydrogen gas and calcium hydroxide, a base. [Merck, 11th ed. 1989].
Hazard
Evolves highly flammable hydrogen when
wet; solid product is slaked lime. Irritating to skin.
Health Hazard
Inhalation or contact with vapors, substance or decomposition products may cause severe injury or death. May produce corrosive solutions on contact with water. Fire will produce irritating, corrosive and/or toxic gases. Runoff from fire control may cause pollution.
Fire Hazard
Produce flammable gases on contact with water. May ignite on contact with water or moist air. Some react vigorously or explosively on contact with water. May be ignited by heat, sparks or flames. May re-ignite after fire is extinguished. Some are transported in highly flammable liquids. Runoff may create fire or explosion hazard.
Description
Calcium hydride is a gray powder (white if pure,
which is rare). It reacts vigorously with water liberating
H2 gas. CaH2 is thus used as a drying agent,
i.e. a desiccant. It is prepared directly from the metal
or by reacting CaCO3 with hydrogen at elevated temperatures. The overall reaction is shown as
follows:
CaCO3＋heat＋H2→CaH2＋H2O＋CO2
CaH2 is a saline hydride, meaning that its structure is
salt-like. The alkali metals and the alkaline earth metals
all form saline hydrides. These species are insoluble in
all solvents with which they do not react because they
have extended structures. CaH2 crystallizes in the
PbCl2 structural pattern.
The reaction of CaH2 with water can be represented
as follows:
CaH2＋2H2O0Ca(OH)2＋2H2
The two hydrolysis products, H2, a gas, and Ca(OH)2,
an aqueous mixture of solid plus liquid (i.e. a slurry), are readily separated from the solvent by distillation, filtration, or decantation.
Physical properties
Grayish orthorhombic crystal or powder; stable at ambient temperature; density 1.70 g/cm3; melts at 816°C; reacts with water and alcohol.
Preparation
Calcium hydride may be prepared from its elements by direct combination of calcium and hydrogen at 300 to 400°C. It also can be made by heating calcium chloride with hydrogen in the presence of sodium metal:
CaCl2 + H2 + 2Na → CaH2 + NaCl
Alternatively, calcium hydride may be prepared by the reduction of calcium oxide with magnesium in the presence of hydrogen:
CaO + Mg + H2 → CaH2 + MgO.
Production Methods
Calcium hydride ignites in air on heating and can explode violently if mixed and rubbed with a strong oxidizing agent such as perchlorate or bromate. Contact with water produces hydrogen which can create a fire hazard in a confined space.
Reactions
Once
ignited, it burns with a strongly exothermic reaction:
CaH2+O2→CaO+H2O
The reaction of calcium hydride with water is
also very exothermic. Heating is necessary to
initiate the reaction with alcohols to form alcoholates. The reaction with ammonia takes place
at 700 ℃ with formation of calcium amide. At
high temperature (600 – 1000℃) calcium
hydride is a powerful reducing agent.
Flammability and Explosibility
Notclassified
reaction suitability
reagent type: reductant
Potential Exposure
Calcium hydride is used as a dryingand reducing agent and a cleaner for blocked up oil wells.
First aid
If this chemical gets into the eyes, remove anycontact lenses at once and irrigate immediately for atleast 30 min, occasionally lifting upper and lower lids. Seekmedical attention immediately. If this chemical contacts theskin, remove contaminated clothing and wash immediatelywith soap and water. Seek medical attention immediately. Ifthis chemical has been inhaled, remove from exposure, beginrescue breathing (using universal precautions, includingresuscitation mask) if breathing has stopped and CPR if heartaction has stopped. Transfer promptly to a medical facility.When this chemical has been swallowed, get medical attention. Give large quantities of water and induce vomiting. Donot make an unconscious person vomit. Medical observationis recommended for 24-48 h after breathing overexposure,as pulmonary edema may be delayed. As first aid for pulmonary edema, a doctor or authorized paramedic may consideradministering a corticosteroid spray.
storage
Color Code—Red Stripe: Flammability Hazard:Do not store in the same area as other flammable materials.Calcium hydride must be stored to avoid contact with wateror steam since violent reactions occur and flammablehydrogen gas is produced. Store in tightly closed containersin a cool, well-ventilated area.
Shipping
Calcium hydride should carry a “DANGEROUSWHEN WET” label. It falls in Hazard Class 4.3 andPacking Group I.
Incompatibilities
Reacts with water, moist air, and steam,releasing flammable hydrogen gas and may self-ignite inair. Incompatible with metal halogenates, silver fluoride,and tetrahydrofuran.
