Description
Hydrogen telluride has the formula, H2Te. The simplest hydride of Te, it is rarely encountered because of its tendency to decompose to the constituent elements. Most compounds with Te–H bonds are unstable with respect to loss of H2. H2Te is chemically and structurally similar to H2S, and both are acidic species with H–X–H angles approaching 90°.The tellurides of the alkaline earth metals tend to immediately decompose on exposure to air, with liberation of tellurium. H2Te is prepared by the acidification of salts of Te
2-,such as Al2Te3 and Na2Te.
Na2Te can be generated by the reaction of Na and Te in anhydrous ammonia. The intermediate in the acidification, the HTe is a stable anion.
H2Te is an endothermic compound, and is unstable in air, rapidly decomposing into water and elemental tellurium:
2H2Te+ O2 → 2H2O+ 2Te
It is almost as acidic as phosphoric acid (pK
a=8.1×10
-3), having a pK
a value of about 2.3×10
-3. It reacts with many metals to form tellurides. However, many of these are unstable relative to their decomposition to the elements. Its CAS number is 7783-09-7 and its molecular weight is 129.6158 g/mol. It is a colorless gas and is toxic if breathed. Its density is 3.310 g/cm3 and its melting point is –49°C with a boiling point of –2.2°C. Its solubility in water is 0.701 g/100 ml of water at 20°C.
Physical properties
Colorless gas; strong garlic-like odor; stable to light when dry but under-goes photochemical decompostion in the presence of moisture and dust; den-sity 5.68 g/L; liquefies to a colorless unstable liquid at -2°C, decomposed bylight; liquid density 2.57 g/mL at -20°C; solidifies at -49°C; soluble in water,alcohol and alkalies; pKa 2.6 (for first dissociation constant at 18°C) and 11.0(the dissociation constant at 25°C) for the second replaceable hydrogen.
Preparation
Hydrogen telluride is prepared by the reaction of aluminum telluride,Al
2Te
3 with hydrochloric acid:
Al2Te
3 + 6HCl → 3H
2Te + 2AlCl
3
It also may be prepared by electrolysis of a 50% sulfuric acid solution using atellurium cathode.
