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1.
Nature
Alkali metal elements are silver-white, with metallic luster, good conductivity, ductility, low hardness, low melting point and low density
.
The melting point of lithium is 180.
Alkali metals are all active metals with strong reducing properties and can directly combine with many non-metallic elements to form ionic compounds
.
Li most active when heated with N 2 reaction
6Li+N 2 =2Li 3 N
The strong reducibility of alkali metals can be used to prepare precious metals or rare metals
.
E.
Alkali metals (except Li) react violently with water due to the low melting point of alkali metals and the greater solubility of their hydroxides
.
A large amount of hydrogen is generated in the reaction and it is prone to explosion.
In the laboratory, it is necessary to use alkali metal element carefully to avoid contact with water
2Na+2H 2 O=2NaOH+H 2
Alkali metals react with H2 at high temperatures to form ionic hydrides
.
For example, NaH can be generated at 380℃
2Na+H 2 O=2NaH
Among them, H is in the -1 oxidation state
.
Among the alkali metal hydrides, LiH is the most stable, melting at 688.
2.
Preparation of simple substance
Alkali metals are active in chemical properties and exist in the form of compounds in nature, which are difficult to reduce
.
Molten salt electrolysis and thermal reduction are commonly used in industry to produce alkali metals in large quantities
Lithium and sodium are usually produced by electrolytic melting of chlorides, while potassium, minerals and tortoises are produced by metal thermal reduction
.
The production of metallic sodium uses graphite as the anode and cast steel as the cathode.
It is obtained by electrolysis of NaCl molten salt at 580°C
.
2NaCl(l)=2Na(1)+Cl 2 (g)
Since the boiling point of Na (883°C) is close to the melting point of NaCl (801°C), CaCl 2 is usually added as a flux to reduce the melting temperature of the salt (the melting point of the mixed salt is about 500°C) to avoid the loss of Na volatilization
.
Lower operating temperature can also reduce the solubility of Na in the melt
Potassium is very soluble in molten chloride, making it difficult to separate.
It is not suitable for production by molten salt electrolysis
.
The industry usually uses its low boiling point (potassium's boiling point of 759°C) to mass-produce metallic potassium by thermal reduction
.
KCI is reduced with metallic Na (boiling point 883°C) at 850°C to obtain metallic potassium
.
Na(1)+KCI(l)=NaCl(l)+K(g)
Potassium escapes and is collected in the form of vapor, with a purity of 99.
99%
.
The production of rubidium and cesium also adopts thermal reduction method, which is obtained by reducing its chloride with metallic calcium
.
The response is as follows
Related links: Elements and compounds of gallium, indium, and thallium
