Calciumhydrid

BeschreibungCalcium 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.

VerwendenTo prepare rare metals by reduction of their oxides; as a drying agent for liquids and gases; to generate hydrogen: 1 g of calcium hydride in water liberates 1 liter of hydrogen at STP; in organic syntheses.

synthetischeCalcium 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.