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Alkali metals or their compounds can make the flame show a characteristic color in a high-temperature flame.
This method is called a flame color experiment
.
Among them, the lithium flame is dark red, the sodium flame is yellow, the potassium flame is purple, the material flame is purple, and the absolute flame is blue
1.
Solubility of salt
Lithium salts have special solubility.
Strong acid salts are easier to dissolve in water, while some weak acid salts have poor solubility, such as LiF, Li 2 CO 3 , and Li 3 PO 4 , which have lower solubility
.
Important alkali metal insoluble salts are: NaBiO 3 , sodium zinc uranyl acetate NaAc·Zn(Ac) 2 ·3UO 2 (Ac)2·9H 2 O (yellow-green), sodium antimonate Na[Sb(OH) 6 ]; KCIO 4 , K 3 [Co(NO 2 ) 6 ] (yellow), potassium hydrogen tartrate KHC 4 H 4 O 6 , potassium tetraphenylborate K[B(C 6 H 5 ) 4 ], K 2 [PtCl 6 ] (Yellow); Rb 2 [SnCl 6 ]; CsClO 4
.
2.
Salt crystal water and double salt
Alkali metals with a small radius have a greater attraction to water molecules and are easy to form crystal hydrated salts
.
However, alkali metal halides generally do not contain water of crystallization
Among nitrates, only lithium nitrate has crystal water (LiNO 3 ·H 2 O, LiNO 3 ·3H 2 O), and other nitrates have no crystal water
.
Crystalline alkali metal sulphate only water of Li 2 SO .
Potassium has a slightly larger radius, and potassium salt is less deliquescent than sodium salt
.
Therefore, the laboratory commonly uses potassium salts as reagents, such as KI, KBr, KMnO 4 , K 2 Cr 2 O 7 and so on
In addition to lithium, alkali metal ions can form a series of double salts, such as KCl·MgCl 2 ·6H 2 O (carnallite), K 2 SO 4 ·Al 2 (SO 4 ) 3 ·24H 2 O (alum), K 2 SO 4 ·MgCl 2 ·6H 2 O (soft potash), K 2 SO 4 ·Cr 2 (SO 4 ) 3 ·24H 2 O (chrome potash)
.
The lower solubility of double salt than simple salt is the main factor in the formation of double salt
3.
Thermal stability of oxo acid salt
The polarizing ability of alkali metal ions affects the thermal stability of its oxo acid salt
.
The smaller the radius of the alkali metal ion, the stronger the polarization ability, the more unstable its oxo acid salt, and the lower the decomposition temperature
Li 2 CO 3 =Li 2 O+CO 2
The difference in the polarization ability of alkali metal ions sometimes also affects the thermal decomposition products of its oxo acid salt
.
Take nitrate as an example.
Due to the strong polarizing ability of lithium ion, the product of thermal decomposition of nitrate is metal oxide; while the thermal decomposition product of other alkali metal nitrate is nitrite, which is decomposed at higher temperature.
Oxide, nitrogen and oxygen
.
4.
Important alkali metal salt
The most important of the alkali metal salts is NaCl, commonly known as table salt and rock salt, which are abundant in sea water (the mass fraction of NaCl is nearly 2.
7%), as well as its minerals (rock salt)
.
NaCl is a necessity in people's daily life and an important chemical raw material
.
Historically, the production of NaOH with NaCl as a raw material was a sign of the beginning of the chemical industry, and Na, NaOH, Cl 2 , Na 2 CO 3 and HCl can be produced with NaCl as a raw material
.
NaCl is also widely used in food processing, petroleum industry, textile industry, etc.
, and the amount used as a road snow remover is also quite large
.
Sodium carbonate Na 2 CO 3 , commonly known as soda and soda ash, is one of the most important alkaline compounds
.
The commercially available product is sodium carbonate Na 2 CO 3 ·10H 2 O containing 10 crystal water , which is easy to lose part of the crystal water and become weathered
.
Sodium carbonate is an important chemical raw material, which is used in the production of pulp, soap, detergent and other chemical reagents
.
The methods of industrial production of sodium carbonate include ammonia-soda method and joint soda production method
.
Sodium bicarbonate NaHCO 3 , commonly known as baking soda, is widely used in food processing and is also an important chemical raw material.
It can be easily dehydrated and converted into Na 2 CO 3 when heated
.
Anhydrous sodium sulfate Na 2 SO 3 , commonly known as sodium sulfate, is widely used in industries such as papermaking and ceramics
.
Sodium sulfate decahydrate Na 2 SO 4 ·10H 2 O, commonly known as Glauber's salt, is an energy storage material
.
Potassium nitrate KNO 3 is widely used as fertilizer; potassium nitrate is oxidizing and explosive, and can be used to make explosives
.
Lithium salt was originally mainly used to produce lithium stearate, which was used as a thickener for lubricants
.
Li 2 CO 3 is used to lower the melting point when electrolyzing lead, and a small dose of oral LiCO 3 can effectively treat manic depression
.
In recent years, lithium batteries and lithium ion batteries have been widely used in electronic products such as smart phones, making the use of lithium and product development more and more attention
.
Related links: Alkali metal oxygenates
