碱金属.（Alkali metal）.docVIP

碱金属.（Alkali metal） I. presence and preparation 1. existence Because alkali metals are chemically active, they exist in nature in a combination state. In alkali, sodium and potassium is widely distributed in the earths crust, their abundance are 2.5. The main mineral is albite, potassium feldspar, Na[AlSi3O8] K[AlSi3O8] and K2SO4.Al2 KCl.MgCl2.6H2O Carnallitite alunite (SO4) 3.24H2O. The amount of NaCl in the water for 2.7, plant ash also contains potassium salt. The important minerals of lithium are spodumene Li2O.Al2O3.4SiO2, and lithium, rubidium and cesium are less abundant and dispersed in nature and are classified as rare metals. 2. preparation Because alkali metals are very lively, they are usually prepared by electrolysis of their molten compounds. Sodium and potassium are produced mainly by electrolytic molten chlorides. The preparation of sodium chloride electrolysis of molten metal sodium The raw material used for electrolysis is the mixed salt of sodium chloride and calcium chloride. If only sodium chloride is used for electrolysis, not only high temperature is needed, but also the sodium (NaCl) and 1073K (1156K) of the electrolyte are easily dispersed in the molten salt, which is difficult to separate. If the calcium chloride, one can reduce the melting point of the electrolyte (mixed salt melting point of about 873K), to prevent the volatilization of sodium, and can reduce the dispersion of sodium metal, because the molten mixture density than sodium, sodium to float. Total response: 2NaCl==, 2Na + Cl2 The electrolytic sodium contains about 1% calcium. Thermal reduction method The methods of making metals are heat reduction, metal substitution and thermal decomposition. Generally, coke or carbide is used as reducing agent in thermal reduction process, for example: K2CO3 + 2C = 2K + 3CO 2KF + CaC2, ====CaF2 + 2K + 2C Metal replacement method Potassium, rubidium and cesium can also be produced by electrolysis, but metals such as Na, Ca, Mg and Ba are ofte