Introduction to Potassium Dichromate
In chemistry, an oxidizing agent is a type of substance that has the ability to oxidize other substances. You may wonder what oxidation means. Oxidation is a phenomenon where a substance can accept electrons from other substances. Some of the most common oxidizing agents are halogens, hydrogen peroxide, oxygen, ozone, chromium hexavalent compounds etc.
Potassium Dichromate is a powerful oxidizing agent. Their typical applications include Leather tanning and screen printing, Metal Treating and corrosion inhibitor, Pyrotechnics and explosives, Photographic engraving, Chromium source in preparing chromium compounds, Pigment preparation, Oil drilling, Electroplating, as a Catalyst for the chromium metal production, and as Wood Preservative. A chemical compound that has a chromium element in its +6oxidation state is known as Hexavalent chromium (Chromium +6, Cr (VI), chromium (VI)). They are considered to be highly toxic as they are genotoxic carcinogens.
What is Potassium Dichromate?
A hexavalent chromium compound that acts as a common inorganic chemical reagent is called potassium dichromate. The chemical formula of potassium dichromate is K2Cr2O7. It is used in many industrial applications and laboratories as a conventional oxidizing agent. Being hexavalent, potassium dichromate is highly toxic in nature and harmful to the skin and body. Potassium dichromate is a crystalline ionic solid with a very bright red-orange colour. Potassium dichromate is more popular in laboratory experiments as it is not deliquescent (a tendency to absorb air moisture and dissolve in it) as compared to most industry-relevant sodium dichromate salts. A reaction of potassium chloride with sodium dichromate gives potassium dichromate.
Na2Cr2O7 + 2KCl → K2Cr2O7 + 2NaCl
Alternatively, it can be obtained from potassium chromate through roasting chromite ore with potassium hydroxide. It ionizes in water:
K2Cr2O7 → 2K+ + Cr2O72−
Cr2O72- + H2O ⇌ 2CrO42- + 2H+
This reaction when performed in the laboratory gives orange-red crystals of potassium dichromate. It is soluble in water. It does not have any distinctive odor. It may, however, severely irritate the eyes and respiratory tract. Avoid contact of potassium dichromate with organic materials. It is noncombustible but most commonly used in pyrotechnic displays along with tungsten and iron.
The Structure of Potassium Dichromate (K2Cr2O7)
The chemical formula of potassium dichromate is K2Cr2O7 with 294.185 g/mol molar mass. 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 each attached to three oxygen atoms as well as a bridging oxygen atom.
Figure 1: Properties of Potassium Dichromate (K2Cr2O7)
Properties of Potassium Dichromate (K2Cr2O7)
Physical Properties:
It forms orange-red crystals which melt at 396oC.
It is easily soluble in hot water but moderately soluble in cold water.
Chemical Properties:
Action of Heat: On heating, K2Cr2O7 decomposes to give potassium chromate with evolution of O2 gas.
4 K2Cr2O7 → 4K2CrO4 + 2Cr2O3 + 3O2
Reaction with Alkalis: When an orange-red solution of K2Cr2O7 reacts with an alkali, a yellow solution is obtained because of the potassium chromate formation.
K2Cr2O7 + 2KOH → 2 K2CrO4 + H2O
Orange-red Yellow
On acidifying the yellow color of K2CrO4 again changes to orange-red due to the reformation of K2Cr2O7.
2K2CrO4 + H2SO4 → K2Cr2O7 + K2SO4 + H2O
The interconversion can be explained on the basis of the fact that in K2Cr2O7 solution, orange-red Cr2O72- ions are in equilibrium with yellow CrO42- ions.
Cr2O72- + H2O → 2CrO42- + 2H+
Orange red Yellow
Oxidization: K2Cr2O7 is known as a powerful oxidizing agent. In presence of dil.H2SO4, one mole of this compound gives three atoms of oxygen as shown below.
K2Cr2O7 + 4H2SO4 → K2SO4 + Cr2 (SO4)3 + 4H2O + 3(O)
Some other examples of oxidizing properties of K2Cr2O7 are given below:
It liberates I2 from KI.
K2Cr2O7 + 7 H2SO4 + 6KI → 4 K2SO4+ Cr2(SO4)3 + 3I2 + 7H2O
It oxidizes ferrous sulfate to ferric sulphate.
K2Cr2O7 + 7H2SO4 + 6FeSO4 → K2SO4 + Cr2(SO4)3 + 3Fe2(SO4)3+ 2H2O
It oxidizes H2S to sulphur.
K2Cr2O7 + 4H2SO4 + 3H2S → K2SO4 + Cr2(SO4)3 + 7H2O + 3S
Chromyl Chloride Test: When salt containing chloride is treated with K2Cr2O7 and con. H2SO4 chromyl chloride (reddish brown) vapors are produced.
K2Cr2O7+ 4KCl + 6 H2SO4 → 2CrO2Cl2 + 6KHSO4 + 3H2O
Chromyl chloride
The reaction is used to detect chloride ions in qualitative analysis.
Properties of the K2Cr2O7 formula
Uses of Potassium Dichromate (K2Cr2O7)
Potassium dichromate has widespread industrial use. Some of its uses are listed below:
K2Cr2O7 is an oxidizing agent for a variety of reactions in laboratories and industries. It is used in the leather industry for chrome tanning by acting as a precursor for potassium chrome alum.
It is used in volumetric analysis.
It is used in dyeing and calico printing.
In photography, K2Cr2O7 is used with strong mineral acid as an oxidizing agent to harden the gelatin film.
It is used to prepare chromic acid, which is used to clean glassware (like other chromium (VI) compounds, sodium dichromate, chromium trioxide). However, due to the toxicity of hexavalent chromium, this practice is now discouraged and discontinued.
K2Cr2O7 finds use in the construction industry as an ingredient in cement.
It is a non-hygroscopic reagent and is used in “wet tests” in analytical chemistry.
It is known as Schwerter’s solution when dissolved in 35 percent nitric acid and used in tests to detect the presence of different metals in determining silver purity.
It is used as wood darkening in the wood tannins that produce deep brown colour on wood. It is an effective treatment for mahogany.
Effects on Health
Potassium dichromate can cause chronic diseases like chromium dermatitis in the hands and forearms.
The toxicity of potassium dichromate can cause harm to animals such as rabbits, rodents etc.
It is toxic to aquatic organisms too and poses a big threat to the environment.
Potassium dichromate is corrosive in nature and its exposure may develop several eye problems or even blindness.
It may cause heritable genetic damage, impaired fertility, and is dangerous to unborn children.
Potassium dichromate is dangerous to the respiratory tract. It can cause ulcers. An increased risk of lung cancer is associated with potassium dichromate, a known human carcinogen.
Eating potassium dichromate can cause serious harm to an individual’s health or sometimes even be killed.
It may be harmful to touch the material. Systemic effects might occur after absorption.
Consuming this substance can cause a chemical burn in the mouth and gastrointestinal tract which causes ingestion.
However, It is rare to become acutely poisoned by eating or swallowing potassium dichromate, because usually vomiting occurs and renal excretion is rapid.
Subsequently, potassium dichromate causes irregular heartbeats, heart block, and blood pressure drop.
Safety hazards
Potassium dichromate is a hexavalent chromium compound, hence it is highly toxic and carcinogenic. Potassium dichromate is very corrosive by nature and it can cause severe irritation in the eye and skin, burning sensation, and even lead to blindness. It is referred to as affecting reproductive health and it acts as a mutagenic agent i.e. it affects the genetic material and harms unborn children.
FAQs on Potassium Dichromate
1. What are the applications of Potassium Dichromate?
The following are the applications of Potassium Dichromate.
It is used to prepare strong cleaning solutions, and different products such as paints, waxes, glues, and so on.
Potassium Dichromate is also used for the production of explosives, ceramics, chemicals of chrome, mordant, varnish, pigments, ink, glass, spices, pharmaceuticals, and so on.
It is also used as an oxidizer, for the production of chromium kalium and chemical reagents.
Other applications of potassium dichromate include the engraving of glass materials, tanning of leather for footwear, and is also used as an oxidizing agent in the photographic printing process.
2. How to handle and store Potassium Dichromate?
It is important to handle potassium dichromate with care, and we should avoid its contact if possible the following are the important points that must be taken into consideration while handling the chemical.
The container of this compound should be kept in a dry place away from heat and sources of ignition.
It should be kept away from combustible materials.
Be sure not to add water to this substance. If ventilation is necessary, use appropriate respiratory equipment.
An individual must avoid contact with skin and eyes as it can cause serious harm.
Potassium dichromate should be kept away from incompatibles such as combustible materials, reducing agents, and organic materials.
This substance must be stored in a separate cabinet or storage room.
If someone finds the symptoms of poisoning, one should seek medical attention.
3. What are the physical properties of Potassium Dichromate?
The following are the physical properties of Potassium Dichromate.
The appearance of this chemical is of red-orange crystals.
The density of this substance in a solid state is 2.676 g/cm3.
Potassium Dichromate usually exists in a solid-state at room temperature.
This compound has a high Refractive index of 1.738.
Potassium Dichromate is odorless i.e. it does not have any smell.
The substance is highly corrosive and is non–combustible.
Potassium Dichromate tends to get decomposed when it reaches boiling point. The boiling point of this substance is 500 °C (932 °F; 773 K), and the melting point is 398 °C (748 °F; 671 K).
The Potassium dichromate has the central atom of Chromium in tetrahedral form. Its Crystalline structure is triclinic.
4. What are the effects of Potassium Dichromate on health?
In the field of inorganic chemistry, Potassium Dichromate is said to be one of the most popular chemical reagents. It is a very strong oxidizing agent. It can cause ongoing infections like chromium dermatitis in the hands and lower arms. This compound is very harmful to amphibian creatures and it is a major danger to the climate too. Potassium dichromate is very harmful, and its acceptance might lead to a few eye issues or even visual deficiency. This substance can also cause weakened ripeness, heritable hereditary harm, and is hazardous to unborn children.
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