Potassium Dichromate - K2Cr2O7

Potassium compounds are quite common and are extremely useful for a variety of purposes. Potash and other potassium compounds have been used for centuries in the manufacture of glass products. Today 95% of the potassium compounds gathered in the world is used in the manufacture of fertilizers.

Potassium dichromate is an inorganic chemical compound possess immense industrial and laboratory importance. It is an orange crystalline solid with the chemical formula K₂Cr₂O₇. It is a strong oxidizing agent and is soluble in water. It is used in the volumetric estimation of ferrous salts, iodides and sulphides for the preparation of chrome alum, chrome yellow and chrome red.

What is Potassium dichromate (K₂Cr₂O₇)?

K₂Cr₂O₇ is an inorganic chemical reagent with chemical name Potassium dichromate. It is also called as Potassium bichromate or Dipotassium bichromate. It is crystalline ionic solid, with a bright red-orange colour. It is odourless and insoluble in acetone as well as alcohol but dissolves in water.

It is widely used as a precursor to potassium chrome alum and leather tanning. It is commonly used as an oxidizing agent in several industries and laboratories. It is highly corrosive and non-combustible. Potassium dichromate is prepared as follows –

• By reacting potassium chloride on sodium dichromate or
• Produced from potassium chromate by the roasting of chromite ore with potassium hydroxide

Properties of Potassium dichromate – K₂Cr₂O₇

Some other important properties of potassium dichromate are listed below.

• K₂Cr₂O₇ has a crystalline, reddish-orange appearance.
• At a temperature of 0^oC, the solubility of this compound in water corresponds to 49 grams per litre.
• This compound is insoluble in alcohol and acetone.
• The heat capacity of K₂Cr₂O₇ is 219 Joules per mole.
• The standard molar entropy of this compound is 291.2 joules per kelvin mole.

Potassium dichromate Structure (K₂Cr₂O₇ Structure)

Potassium  Dichromate molecules feature two ionic bonds between the two positively charged potassium cations and the dichromate anion, which holds a charge of -2. The dichromate ion features two chromium atoms that are bonded to four different oxygen atoms. Two of these Cr-O bonds are double bonds and one of the oxygen atoms is bonded to both the chromium atoms. The last oxygen atoms that are singly bonded to the chromium atom hold a charge of -1 (as illustrated below).

Structure of Potassium Dichromate Molecules

Potassium dichromate (K₂Cr₂O₇ ) Uses

• Used in cement to retard the setting of the mixture and to improve its density along with the texture.
• It is used in photographic screen printing.
• It is a common reagent used in analytical chemistry for classical “wet tests”.
• It is used to stain certain type of woods to produce deep, rich browns.
• It is used to clean glassware and as an etching material.
• Used in pyrotechnic displays along with iron and tungsten.
• Medically it can be used externally as an antiseptic, caustic, and astringent.

Potassium dichromate is known to form an analytical reagent known as Schwerter’s solution when it is dissolved in an approximately 35 per cent nitric acid solution. This reagent can be used to test for the presence of different metals, especially for silver purity determination. Pure silver is known to make the solution bright red whereas sterling silver is known to impart to it a dark red colour. Furthermore, low-quality coin silver  turns this solution brown (mainly because of the presence of copper that turns the solution brown). It can also be noted that 0.500 silver would turn Schwerter’s solution green. Although gold and palladium do not shift, brass turns this solution dark brown whereas copper imparts a brown colour. Finally, the metals lead and tin form yellow solutions when introduced to a solution of potassium dichromate in 35% (approx.) nitric acid.

Effects on Health

• Potassium dichromate primarily affects the respiratory tract which causes ulcerations. K₂Cr₂O₇ is a known human carcinogen with an increased risk of developing lung cancer.
• Toxic effects can result from accidental ingestion of the material, animal experiments show that ingestion of fewer than 40 grams can be deadly or cause severe harm to the individual’s health.
• After ingestion, the material can generate chemical burns in the oral cavity and gastrointestinal tract.
• After swallowing, acute potassium poisoning is uncommon because generally vomiting occurs and renal excretion is rapid.
• Potassium creates a slow, weak pulse, heart rhythm irregularities, heart block and blood pressure drop eventually.
• Skin contact with the material may be detrimental; after absorption, systemic impacts may lead

Learn more about the chemical behaviour and importance of Potassium dichromate with the expert faculties at BYJU’S.

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