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The binary compounds formed by alkali metals and oxygen include ordinary oxides, peroxides, superoxides and ozonides
.
The oxygen in the peroxide M 2 O 2 has no single electrons, is a diamagnetic substance, and the OO bond level is 1
.
Alkali metals burn in sufficient air, Li generates ordinary oxides Li 2 O, Na generates peroxides Na 2 O 2 , and K, Rb, and Cs generate superoxides KO 2 , RbO 2 , and CsO 2
.
The dry hydroxide powder of Na, K, Rb, and Cs reacts with O 3 to generate ozonide MO 3
.
1.
Ordinary Oxide
Lithium oxide Li 2 O can be obtained by burning elemental Li in sufficient air, sodium oxide Na 2 O can be made by reducing sodium nitrite with sodium azide , and potassium oxide K 2 O can be made by reducing potassium nitrate with elemental potassium .
.
From alkali metal oxide of Li 2 O to Cs 2 gradually deepened O color
.
Li 2 O and Na 2 O are white, K 2 O is light yellow, Rb 2 O is bright yellow, and Cs 2 O is orange-red
.
Alkali metal oxides react with water to form corresponding hydroxides and emit a lot of heat
.
2.
Peroxide
All alkali metals can form peroxides
.
Peroxide can be regarded as a salt of H 2 O 2 and its stability increases as the radius of alkali metal ions increases
.
The least stable Li 2 O 2 decomposes above 195°C, while Na 2 O 2 decomposes above 675°C
.
The hydrated lithium hydroxide LiOH·H 2 O reacts with hydrogen peroxide to form LiOOH·H 2 O, which is slowly heated and dehydrated under reduced pressure to obtain Li 2 O 2
.
Metal Na burns in sufficient air to generate Na 2 O 2
.
2Na+O 2 =Na 2 O 2
Alkali metal peroxide reacts with water or dilute acid to generate hydrogen peroxide
.
Na 2 O 2 +2H 2 O=2NaOH+H 2 O 2
Na 2 O 2 +H 2 SO 4 =Na 2 SO 4 +H 2 O
The generated hydrogen peroxide is unstable and easily decomposes to release oxygen
.
Alkali metal peroxides are alkaline and react with CO 2 to release oxygen
.
2Na 2 O 2 +2CO 2 =2Na 2 CO 3 +O 2
Na 2 O 2 is often used as a CO 2 absorbent in gas masks and submarines and provides oxygen
.
Li 2 O 2, which has the lightest mass, is usually used in aerospace airtight cabins
.
Alkali metal peroxides have strong oxidizing properties
.
For example, Na 2 O 2 can oxidize Fe to Na 2 FeO 4 and Cr 2 O 3 to Na 2 CrO 4
.
Here, Na 2 O 2 is not only an oxidizing agent, but also a melting agent
.
Peroxides are also reductive and will be oxidized when encountering strong oxidants
.
5Na 2 O 2 + 2MnO .
4 - + 16H + = 5O 2 + 2Mn 2 + + 10Na + + 8H 2 O
3.
Superoxide and ozonide
Li cannot form superoxide, and Na superoxide is also very unstable
.
This is mainly because Li + and Na + have small radii and strong polarization ability
.
The cationic superoxides KO 2 , RbO 2 and CsO 2 with large radius are relatively stable and can be prepared by burning simple substances in sufficient air
.
Superoxides have colors, KO 2 is orange, RbO 2 is dark brown, and CsO 2 is orange
.
Superoxide can also absorb CO 2 and release oxygen, which decomposes into oxide and oxygen at high temperature
.
Superoxide is highly oxidizing and reacts violently with water or other protic solvents to generate oxygen and hydrogen peroxide
.
2KO 2 +2H 2 O=O 2 +H 2 O 2 +2KOH
Li cannot form ozonide
.
The dry hydroxide powder of Na, K, Rb, and Cs reacts with ozone O 3 to generate the corresponding ozonide MO 3
.
4KOH+4O 3 =4KO 3 +2H 2 O+O 2
The ozonide reacts with water to form hydroxide and release oxygen
.
4KO 3 +2H 2 O=4KOH+5O 2
The ozonide is unstable and can slowly decompose into superoxide at room temperature
.
2KO 3 =2KO 2 +O 2
4.
Hydroxide
Alkali metal hydroxides are strong bases, which are easy to absorb moisture in the air, dissolve in water and emit a lot of heat
.
The solubility of hydroxide increases as the radius of alkali metal ions increases
.
The most important of the alkali metal hydroxides is sodium hydroxide NaOH, also known as caustic soda, caustic soda and caustic soda
.
The main method of industrial production of sodium hydroxide is the electrolysis of sodium chloride aqueous solution, and the specific methods include mercury cathode method, diaphragm method and ion membrane method
.
