-
Categories
-
Pharmaceutical Intermediates
-
Active Pharmaceutical Ingredients
-
Food Additives
- Industrial Coatings
- Agrochemicals
- Dyes and Pigments
- Surfactant
- Flavors and Fragrances
- Chemical Reagents
- Catalyst and Auxiliary
- Natural Products
- Inorganic Chemistry
-
Organic Chemistry
-
Biochemical Engineering
- Analytical Chemistry
- Cosmetic Ingredient
-
Pharmaceutical Intermediates
Promotion
ECHEMI Mall
Wholesale
Weekly Price
Exhibition
News
-
Trade Service
From the elemental potential diagram of chromium, it can be seen that hexavalent chromium is easily reduced to trivalent chromium, and divalent chromium is easily oxidized to trivalent chromium.
The most stable oxidation state of chromium is +3
.
1.
Oxides and hydroxides
Cr 2 O 3 is a dark green solid with a high melting point.
It is often used as a green paint, commonly known as chrome green
.
Cr 2 O 3 is slightly soluble in water, isomorphous with Al 2 O 3 and has amphoteric properties
The Cr 2 (SO 4 ) 3 solution is used for electroplating
.
Similar to a-Al 2 O 3 , Cr 2 O 3 burned at high temperature is insoluble in acids and alkalis
.
It needs to be eutecticized with K 2 S 2 O 4 to be converted into water-soluble salts Cr 2 (SO 4 ) 3 and K 2 SO 4
Similar to the amphoteric of Al(OH) 3 , Cr(OH) 3 is also amphoteric, soluble in acids and strong bases
.
Cr(OH) 3 +NaOH=Na[Cr(OH) 4 ]
2.
Salts and coordination compounds
The anhydrous trihalide CrF 3 (green), CrCl 3 (purple red), and CrBr 3 (dark green) solids are relatively stable and will not decompose when heated to the melting point
.
Trivalent chromium salts are often prone to crystal water, colorful in color, and similar in composition to the corresponding aluminum salts
.
CrCl 3 ·6H 2 O is a common chromium salt.
It is a coordination compound and has different colors due to different inner boundary ligands
If [of Cr (H 2 O) .
6 ] 3+ inner boundary H 2 O was gradually NH2 .
The important coordination compounds of trivalent chromium are K 3 [Cr(C 2 O 4 )] 3H 2 O (purple), K 3 [Cr(NCS) 6 ] 4H 2 O (purple), K 3 [ Cr(CN) 6 ] (yellow), [Cr(en 3 )]I 3 (yellow)
.
The presence of NH 4 + inhibits the dissociation of NH 3 ·H 2 O and facilitates the coordination of NH 3
.
However , the coordination reaction between Cr 3+ and ammonia is still incomplete, so NH 3 ·H 2 O cannot be used to separate Al 3+ and Cr 3+ , but the reducibility of Cr(Ⅲ) in alkaline solution is used.
, So that it can be converted into soluble CrO 4 2- .
Al(OH) 3 is a colloidal precipitate, which is difficult to filter
.
Adjust the solution to weak acidity with acetic acid to dissolve Al(OH) 3 , and then add BaCl 2 solution to make CrO 4 2- to generate BaCrO 4 precipitation to achieve the purpose of separation
.
Similar to AlCl 3 ·6H 2 O, CrCl 3 ·6H 2 O is hydrolyzed when heated and dehydrated
.
Chromium sulfate is not hydrolyzed during heating and dehydration, because the product H 2 SO 4 does not volatilize
.
Chromium sulfate has different colors due to different crystal water content, such as Cr 2 (SO 4 )3·18H 2 O (purple), Cr 2 (SO 4 ) 3 ·6H 2 O (green), Cr 2 (SO 4 ) 3 (red)
.
And of Al 3+ similar, of Cr 3 + due to the high charge, easy and OH - binding, gray-blue hydrolysis of Cr (OH) in an alkaline solution 3 precipitate
.
Important Cr(Ⅲ) compounds or complexes include Cr(NO 3 ) 3 ·9H 2 O (purple), K 3 [Cr(CN) 6 ] (yellow), K 2 [Cr(C 2 O 4 ) 3 ]·3H 2 O (purple), K 3 [Cr(NCS) 6 ]·4H 2 O (purple)
.
3.
Reducibility
Cr(Ⅲ) has strong reducibility in alkaline solution and is easily oxidized to the highest price
.
Strong oxidizing agent is needed in acid solution to oxidize Cr(Ⅲ)
.
