He potassium dichromate Is an inorganic compound of formula K 2 Cr 2 O 7. It is characterized as being a powerful oxidizing agent.
It is an ionic compound with two potassium ions (K +) and negatively charged dichromate ion (Cr2O7-), in which two hexavalent chromium atoms (with oxidation state +6) are bound to three oxygen atoms, as well as one atom Of oxygen bridge (Potassium Dichromate Formula, SF).
Figure 1: Structure of potassium dichromate.
In the United States it is usually prepared by the reaction of potassium chloride on sodium dichromate according to the equation:
2KCl + Na 2 Cr 2 OR 7 → K 2 Cr 2 OR 7 + 2NaCl
In Germany it is obtained from potassium chromate produced by toasting the chromium ore with potassium hydroxide (O'Neil, 2013).
Potassium dichromate occurs naturally in mineral form as lopezite, a very rare mineral. The compound is toxic and highly carcinogenic.
Figure 2: mineral lopezite.
Physical and chemical properties
Potassium dichromate are orange or odorless triclinic crystals with a metallic taste (National Center for Biotechnology Information, 2017). Their appearance is shown in figure 3.
Figure 3: appearance of potassium dichromate.
The compound has a molecular weight of 294.185 g / mol, a density of 2.666 g / ml, a melting point of 398 ° C and a boiling point of 500 ° C, where it is decomposed (Royal Society of Chemistry, 2015).
The potassium dichromate is very soluble in water, being able to dissolve 45 mg / l at 25 ° C. In aqueous solution it is easily ionized in water to produce the chromate ions (CrO 4 2- ) And dichromate (Cr 2 OR 7 2- ) in equilibrium. It is a moderately oxidizing agent widely used in organic chemistry.
On heating it decomposes to give potassium chromate (K 2 CrO 4 ) And chromic anhydride (CrO 3 ) With the evolution of oxygen according to the equation:
4K 2 Cr 2 OR 7 → 4K 2 CrO 4 + 2Cr 2 O3 + 30 2
Reacts reversibly with bases such as potassium carbonate (K 2 CO 3 ) To give a yellow solution of chromate salts:
K 2 Cr 2 OR 7 + K 2 CO3 → 2K 2 CrO 4 + CO 2
Reacts with cold and dilute acids to give chromic anhydride and with concentrated acids, gives chromate salts and oxygen.
Potassium or sodium dichromate reacts explosively with hydrazine. A drop of anhydrous hydroxylamine on powdered potassium dichromate produces a violent explosion (POTASSIUM BICHROMATE, 2016).
Reactivity and hazards
Oxidizing agents, such as chromate and potassium dichromate, may react with the reducing agents to generate heat and products which may be gaseous (causing pressurization of the closed containers).
The products may be capable of additional reactions (such as combustion in the air). The chemical reduction of the 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 acts as a mutagenic agent (affects genetic material and harms unborn children) (POTASSIUM DICHROMATE, 2016).
Cr (VI) is classified as a human carcinogen known to the exposure inhalation route. The results of occupational epidemiological studies of workers exposed to chromium are consistent between the researchers and the study populations.
Dose-response relationships have been established for exposure to chromium and lung cancer. Workers exposed to chromium are exposed to both Cr (III) and Cr (VI) compounds.
The carcinogenesis of hexavalent chromium may 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 intermediates of Cr (V) and Cr (IV) and reactive oxygen species. During the reduction of Cr (VI) several potentially mutagenic DNA lesions are formed.
In case of contact with eyes, contact lenses should be checked and removed. Then immediately flush eyes with copious amounts of water for at least 15 minutes with cold water.
In case of contact with the skin, 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 skin contaminated with an anti-bacterial cream
In case of inhalation, remove to fresh air. If not breathing, give artificial respiration. If breathing is difficult, give oxygen.
If the compound is ingested, do not induce vomiting unless directed to do so 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 for aquatic life in high concentrations. Chromium is probably produced as insoluble oxide (CrIII) (Cr2O3.nH2O) in soil, as soil organic matter is expected to reduce any soluble chromates to insoluble chromium oxide (Cr2O3).
Chromium in the soil can be transported to the atmosphere by the formation of aerosols. Chromium is also transported from the soil through runoff and water leaching. Most of the chromium in surface waters may be present in particles as sediment.
Part of the particulate chromium would remain as suspended matter and, ultimately, would be deposited in the sediments. Chromium is generally present as (CrIII) in the 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.
Handling and storage
- Potassium dichromate should be handled with care, avoiding contact if possible.
- Keep the container in a dry place away from heat and sources of ignition.
- Keep away from combustible materials. Do not breathe dust.
- Do not add water to this product if ventilation is inadequate, use appropriate respiratory equipment.
- In case of symptoms of poisoning, seek medical attention and show the label to medical personnel when 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 cabinet or storage room (National Institute for Occupational Safety and Health, 2014).
Applications
Potassium dichromate is used to:
- Prepare strong cleaning solutions.
- Prepare various products such as waxes, paints, glues, etc.
- It is used in pyrotechnic exhibitions with tungsten and iron.
- 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 may change their appearance or color in the presence of potassium dichromate. This is particularly useful when you want mahogany or furniture floors to show their rich brown colors.
- Other uses of potassium dichromate include the tanning of leather for footwear, as an oxidizing agent in the photographic printing process and during the cleaning of glassware or engraving 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 and mordant dyeing agents
- The enamel industry applies it to mix with the feldspar powder and quartz sand to calcine enamel powder as a green coloring agent. It can be used for modulation, playing the role of oxidation and the effect of moisture.
- It 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 metal passivation. The compound is also used as a raw material for oxidants for organic synthesis and catalysts, as well as pharmaceuticals.
- It is also used for the manufacture of chemicals of chrome, mordant, ink, glass, spices, pigments, ceramics, varnish, explosives and pharmaceuticals, etc.
- It can be used as an oxidizer, for the manufacture of chromium kalium and for the manufacture of chemical reagents
- It can be used as reference reagent, redox reagent, chromatographic analysis reagent and oxidant, as well as to be used in organic synthesis (potassium dichromate, 2016).
References
- Material Safety Data Sheet Potassium dichromate. (2013, May 21). Retrieved from sciencelab.com.
- National Center for Biotechnology Information. (2017, March 11). PubChem Compound Database; CID = 24502. Retrieved from PubChem.
- National Institute for Occupational Safety and Health. (2014, July 1). POTASSIUM DICHROMATE.
- O'Neil, M. (2013). The Merck Index - An Encyclopedia of Chemicals, Drugs, and Biologicals. Cambridge: Royal Society of Chemistry.
- POTASSIUM BICHROMATE. (2016). Recovered from cameochemicals.
- Potassium dichromate. (2016). Recovered from chemicalbook.
- POTASSIUM DICHROMATE. (2016, October 25). Retrieved from toxnet.
- Potassium Dichromate Formula. (S.F.). Recovered from softschools.com.
- Reid, D. (S.F.). Potassium Dichromate: Definition, Formula & Uses. Retrieved from study.com.
- Royal Society of Chemistry. (2015). Potassium dichromate. Recovered from chemspider.com.