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15.
5.
1 Hydroxides and oxides
Zinc hydroxide Zn(OH) 2 is white and amphoteric.
It is not only soluble in acid, but also soluble in strong alkali
.
Zn(OH) 2 +2OH=[Zn(OH) 4 ] 2-
Cd(OH) 2 is white, slightly amphoteric but obviously alkaline
.
[Cd(OH) 4 ] 2- is slowly formed only in hot and concentrated strong alkali , but there is no obvious dissolution
Pure ZnO is white, commonly known as zinc white, and turns yellow when heated (the escape of oxygen causes lattice defects)
.
ZnO is stable, non-toxic, resistant to H 2 S erosion, and is a high-quality additive
CdO is brown (particle size or lattice defects may have different colors), stable (sublimation by heat, but not easy to decompose)
.
CdO can be used to produce decorative glass, enamel, organic matter hydrogenation and dehydrogenation catalysts
CdO is an alkaline oxide, while ZnO is an amphoteric oxide
.
Both Zn(OH) 2 and Cd(OH) 2 can be dissolved in ammonia water to form colorless complex ions
.
15.
5.
The strong acid salts of zinc and cadmium are both soluble in water
.
The ZnCl 2 solution becomes acidic due to the hydrolysis of Zn 2+
Zn 2+ +H 2 O=[Zn(OH)] + +H +
Therefore, anhydrous ZnCl 2 cannot be obtained by evaporating the solution or heating the ZnCl 2 crystal containing crystal water .
ZnCI2 2 concentrated solution due to the formation of H [ZnCI2 2 (OH)] having significant acidity, capable of dissolving the metal oxide
.
Use this property to remove oxides on the metal surface
FeO+2H[ZnCl 2 (OH)]=Fe[ZnCl 2 (OH)]+H 2 O
Zinc sulfide ZnS (white) and cadmium sulfide CdS (yellow) are insoluble in water
.
ZnS is soluble in dilute hydrochloric acid
The co-precipitation of ZnS and BaSO 4 forms a mixture of ZnS·BaSO 4 called lithopone, which is a good white pigment
.
CdS is called cadmium yellow and can be used as yellow pigments and composite fluorescent materials
.
Both Zn 2+ and Cd 2+ are easy to generate four-coordinate tetrahedral ligand ions, both of which are colorless, such as [Zn(NH 3 ) 4 ] 2+ , [Cd(NH 3 ) 4 ] 2+ , [Zn( the CN) .
4 ] 2- , [of Cd (the CN) .
4 ] 2- and the like
.