The potassium dichromate It is an inorganic compound with the formula K2Cr2O7 characterized by being a powerful oxidizing agent. It is an ionic compound with two potassium ions (K +) and the negatively charged dichromate ion (Cr2O7-), in which two hexavalent chromium atoms (with oxidation state +6) are attached to three oxygen atoms, as well as one atom bridging oxygen (Potassium Dichromate Formula, SF).
In the United States it is usually prepared by the reaction of potassium chloride on sodium dichromate according to the equation: 2KCl + NatwoCrtwoOR7 → KtwoCrtwoOR7 + 2NaCl. In Germany it is obtained from potassium chromate produced by roasting chromium ore with potassium hydroxide (O'Neil, 2013).
Potassium dichromate occurs naturally in the mineral form as lopezite, a very rare mineral. The compound is toxic and highly carcinogenic.
Article index
Potassium dichromate is an odorless orange or red triclinic crystal with a metallic taste (National Center for Biotechnology Information, 2017). Its appearance is shown in figure 3.
The compound has a molecular weight of 294.185 g / mol, a density of 2.676 g / ml, a melting point of 398 ° C and a boiling point of 500 ° C, where it decomposes (Royal Society of Chemistry, 2015).
Potassium dichromate is very soluble in water, being able to dissolve 45 mg / l at 25 ° C. In aqueous solution, it ionizes easily in water to produce chromate ions (CrO4two-) and dichromate (CrtwoOR7two-) in equilibrium. It is a mild oxidizing agent widely used in organic chemistry..
On heating it decomposes to give potassium chromate (KtwoCrO4) and chromic anhydride (CrO3) with the evolution of oxygen according to the equation:
4KtwoCrtwoOR7 → 4KtwoCrO4 + 2CrtwoO3 + 3Otwo
Reacts reversibly with bases such as potassium carbonate (KtwoCO3) to give a yellow solution of chromate salts:
KtwoCrtwoOR7 + KtwoCO3 → 2KtwoCrO4 + COtwo
Reacts with cold and dilute acids to give chromic anhydride and with concentrated acids, gives chromate and oxygen salts.
Potassium or sodium dichromate reacts explosively with hydrazine. A drop of anhydrous hydroxylamine on powdered potassium dichromate produces a violent explosion (POTASSIUM BICHROMATE, 2016).
Oxidizing agents, such as chromate and potassium dichromate, can react with reducing agents to generate heat and products that can be gaseous (causing pressurization of closed containers).
Products may be capable of additional reactions (such as combustion in air). Chemical reduction of materials in this group can be rapid or even explosive, but often requires initiation (heat, spark, catalyst, addition of a solvent).
As a hexavalent chromium compound, potassium dichromate is carcinogenic and highly toxic. It is also very corrosive and on contact with the skin and / or eyes can cause severe irritation and burning sensation, and even lead to blindness..
It is also known to affect reproductive health and act as a mutagenic agent (affects genetic material and harms unborn children) (POTASSIUM DICHROMATE, 2016).
Cr (VI) is classified as a known human carcinogen by inhalation route of exposure. The results of occupational epidemiological studies of workers exposed to chromium are consistent among researchers and study populations..
Dose-response relationships have been established for chromium exposure and lung cancer. Workers exposed to chromium are exposed to both Cr (III) and Cr (VI) compounds.
Carcinogenesis of hexavalent chromium can result from the formation of mutagenic oxidative DNA lesions after intracellular reduction to the trivalent form.
Cr (VI) readily passes through cell membranes and is rapidly reduced intracellularly to generate reactive Cr (V) and Cr (IV) intermediates and reactive oxygen species. During Cr (VI) reduction, several potentially mutagenic DNA lesions are formed.
In case of contact with the eyes, the contact lenses should be checked and removed. Next, it is necessary to immediately flush the eyes with plenty of water for at least 15 minutes with cold water.
In case of skin contact, the affected area should be rinsed immediately with plenty of water for at least 15 minutes while removing contaminated clothing and shoes. Cover irritated skin with an emollient and wash clothing and shoes before reuse. If the contact is severe, wash with a disinfectant soap and cover the contaminated skin with an antibacterial cream.
In case of inhalation, the victim should be moved to a cool place. If not breathing, artificial respiration is given. If breathing is difficult, give oxygen.
If the compound is ingested, vomiting should not be induced unless directed by medical personnel. Loosen tight clothing such as a shirt collar, belt, or tie.
In all cases, medical attention should be obtained immediately (Material Safety Data Sheet Potassium dichromate, 2013).
The compound is harmful to the environment. It is dangerous to aquatic life in high concentrations. Chromium is probably produced as the insoluble oxide (CrIII) (Cr2O3.nH2O) in the soil, as organic matter in the soil is expected to reduce any soluble chromate to insoluble chromic oxide (Cr2O3).
Chromium in soil can be transported to the atmosphere through the formation of aerosols. Chromium is also transported from the ground through runoff and water leaching. Most of the chromium in surface waters can be present in particulate matter as sediment.
Some of the particulate chromium would remain as suspended matter and would ultimately be deposited in the sediments. Chromium generally occurs as (CrIII) in soil and is characterized by its lack of mobility, except in cases where Cr (VI) is involved. Chromium (VI) of natural origin is rarely found.
-Potassium dichromate should be handled with care, avoiding contact if possible.
-The container should be kept in a dry place away from heat and sources of ignition..
-Keep away from combustible materials Do not breathe dust.
-Water should not be added to this product if ventilation is insufficient, suitable respiratory equipment should be worn.
-In case of symptoms of poisoning, seek medical attention and show the label to medical personnel whenever possible..
-Avoid contact with skin and eyes. Keep away from incompatibles such as reducing agents, combustible materials, organic materials.
-Oxidizing materials should be stored in a separate safety storage room or cabinet (National Institute for Occupational Safety and Health, 2014).
Potassium dichromate is used to:
-Prepare strong cleaning solutions.
-Prepare various products such as waxes, paints, glues, etc..
-Used in pyrotechnic displays with tungsten and iron.
-It is commonly used in the laboratory as an analytical reagent, different reactions are carried out with potassium dichromate, among them the concentration of ethanol by reverse titration, the determination of silver and sulfur dioxide, among others..
-Potassium dichromate is also used in industry. For example, the construction industry uses this chemical in cement products to improve density and texture..
-Certain woods can change their appearance or color in the presence of potassium dichromate. This is particularly useful when you want your mahogany wood floors or furniture to show off their rich brown colors..
-Other uses of potassium dichromate include the tanning of shoe leather, as an oxidizing agent in the photographic printing process and during the cleaning of glassware or etching of glass materials (Reid, S.F.).
-The compound can be used for the production of chromium alum, green chromium oxide, chromium yellow pigments, welding electrodes, printing inks, as well as used for enamel coloring agents and mordant dyeing.
-It is applied by the enamel industry to mix with feldspar powder and quartz sand to calcine into enamel powder as a green coloring agent. Can be used for modulation, playing the role of oxidation and moisture effect.
-Can be used as mordants for dye, dye medium and printing. It is also used as an oxidizing agent for synthetic perfume. It is commonly used to weld electrodes, printing inks, and passivation of metals. The compound is also used as a raw material for oxidants for organic synthesis and catalysts, as well as pharmaceuticals..
-It is also used to make chemicals from chromium, mordant, ink, glass, spices, pigments, ceramics, varnish, explosives, and pharmaceuticals, etc..
-It can be used as an oxidant, for the manufacture of chromium kalium and for the manufacture of chemical reagents
-It can be used as a reference reagent, redox reagent, chromatographic and oxidant analysis reagent, as well as being used in organic synthesis (potassium dichromate, 2016).
Yet No Comments