Potassium Chromate. Obtaining, chemical and physical properties. Application

Potassium chromium or chromium-fiber potassium (international names: Kalium chromicum, Kaliumchromat, Potassium chromate) is an inorganic compound, yellow crystals of rhombic system, soluble in water. Refers to chromic acid salts of H2CrO4, which does not exist in the free state. The substance of the potassium chromate is the following formula: CrK2O4

How is potassium chromate obtained?

Potassium chromium is obtained in several ways:

1. By oxidation of potassium chromium oxide with chlorate (reaction occurs at a temperature of 500-700 degrees):

Cr2O3 (chromium oxide) + KClO3 (potassium chlorate) + K2CO3 (potassium carbonate) = 2K2CrO4 (potassium chromate) + KCl (potassium chloride) + 2CO2 (carbon dioxide)

2. By dissolving the chromium oxide in potassium hydroxide :

CrO3 (chromium oxide) + 2KOH (potassium hydroxide) = K2CrO4 (potassium chromate) + H2O (water)

3. By decomposition of potassium dichromate with its heating (the reaction is carried out at a temperature of 500-600 degrees):

4K2Cr2O7 (potassium bichromate) = 4K2CrO4 (potassium chromate) + 2Cr2O3 (chromium oxide) + 3O2 (oxygen)

4. By the action of a concentrated solution of potassium hydroxide on potassium bichromate :

K2Cr2O7 (potassium dichromate) + 2KOH (potassium hydroxide) = 2K2CrO4 (potassium chromate) + H2O (water)

5. In nature, a mineral is rarely found, which is called "tarapacate." This is chromium-fiber potassium with impurities.

Chemical properties of potassium chromate:

1. In dilute acids, chromium-fiber potassium is converted to potassium dichromate, the formula of which is K2Cr2O7. An example is the following reaction:

2K2CrO4 (potassium chromate) + 2HCl ( dilute hydrochloric acid ) = K2Cr2O7 (potassium dichromate) + 2KCl (potassium chloride) + H2O (water)

2. When interacting with concentrated acids, another reaction occurs, for example:

K2CrO4 (potassium chromate) + 2HCl (concentrated hydrochloric acid) = K (Cr (Cl) O3) ( chromium complex complex ) + KCl (potassium chloride) + H2O (water)

3. When interacting with hot concentrated potassium acids, chromate exhibits oxidative properties. An example is the following reaction, carried out at a temperature of 90 degrees:

2K2CrO4 (potassium chromate) + 16HCl (hydrochloric acid) = 2CrCl3 (chromium chloride) + 3Cl2 (chlorine in the form of gas) + 4KCl (potassium chloride) + 8H2O (water)

4. Chromium-fiber potassium can enter into exchange reactions. For example:

K2CrO4 (potassium chromate) + 2AgNO3 (silver nitrate) = Ag2CrO4 (silver chromate precipitates) + 2KNO3 (potassium nitrate)
K2CrO4 (potassium chromate) + Hg2 (NO3) 2 (mercury nitrate) = Hg2CrO4 (mercury chromate precipitated) + 2KNO3 (potassium nitrate)

Physical properties of potassium chromate:

1. The density is 2.732 g / cm3.
2. The potassium chloride melts at a temperature of 968.3 ° C. At a temperature of 668 degrees goes into the red hexagonal phase - it acquires a different color - red. However, upon cooling, it becomes yellow again.
3. Forms crystals of yellow color of a rhombic system.
4. Belongs to the space group P-nam.
5. Refers to paramagnets.
6. Poorly soluble in ethanol, soluble in water. Insoluble in ethyl and diethyl alcohol.
7. The molar mass is 194.19 g / mol.

Optical properties of potassium chromate:

The refractive index is 1.74

Where is potassium chromate applied?

1. In the leather industry is used as a tanning agent. When dyeing fabrics is used as a mordant.
2. It is used as one of the components of the composition of electrolytes of special chemical degreasing.
3. As a bleach for wax and oil.
4. In organic synthesis as an oxidizer, for example, in the production of dyes.
5. Also, chromium-fiber potassium is used to prepare electrochemical silver oxidation solution and for passaging products from copper and silver alloys.
6. In medicine it is used as a homeopathic remedy.
7. A mixture of equal volumes of concentrated sulfuric acid and a solution of K2Cr2O7 saturated in the cold beforehand is used in dishwashing laboratories.

Potassium dichromate (technical name - hrompeak)

It is a crystal of red-orange color. It does not form crystalline hydrates, has a density of 2.684 grams per cubic centimeter, melts at a temperature of 397 degrees. Upon further heating, it decomposes. The solubility in water at 20 degrees is equal to 12.48 grams of salt per 100 grams of water. Potassium dichromate has been widely used as an oxidizer in pyrotechnics, the match industry and in chromometry as a reagent.