Dichromic acid: formula and characteristics

He Dichromic acid Is an unstable dibasic oxidizing acid known only in solution and in the form of dichromatic salts (such as potassium dichromate) whose coloration is orange or red.

Its chemical formula is H2Cr2O7 and can be obtained from two molecules of chromic acid, with loss of one molecule of water. It is hygroscopic and absorbs moisture from the environment.

Source: colourchromes.com

2 H2CrO4 -> H2Cr2O7 + H2O

The ions that form the dichromic acid are:

Cr2O7 -2 dichromate anion and two cations H +

A dichromic acid compound is potassium dichromate which is a good oxidant.

Molecular formula


Chemical names

Dichromic acid; Dichromic acid (VI); Chromic acid (H2Cr2O7); 13530-68-2; Dichromic acid (H2Cr2O7)

Chemical and physical properties

Calculated properties

  • Molecular weight: 218.001 g / mol
  • Donor hydrogen bonds: 2
  • Hydrogen bond acceptor: 7
  • Rotary Bonus Account 2
  • Exact mass 218.0039 g / mol
  • Monisotope mass 217.861 g / mol
  • Count of heavy atoms 9
  • Formal Charge 0
  • Complexity 221
  • Number of isotopic atoms 0

Potassium dichromate

Potassium dichromate is a dichromic acid that has a wide range of uses, acts as an oxidizer in many chemical and industrial applications and in the dyeing, staining and tanning of leather.

It is also used medically as an external or astringent antiseptic and is present in some veterinary drugs. Potassium dichromate is considered to be highly toxic and is a corrosive poison if ingested internally. For this reason, it must be handled with extreme care. The compound is a crystalline ionic solid and has a very bright reddish-orange color.


Potassium dichromate is odorless, its boiling point is 500 degrees Celsius. Potassium dichromate has a melting point of 398 degrees Celsius and a molecular weight of 294.18 grams per mole.

Potassium dichromate can be classified as a hexavalent chromium compound due to its oxidation state. The oxidation state is a calculated number that indicates how many electrons are lost or gained in the atom of a compound.

If the oxidation state is positive, there was a loss of electrons. Negative oxidation states indicate an electron gain for a particular atom. Hexavalent chromium compounds, such as potassium dichromate, contain the chromium element in its oxidation state of 6+.


Potassium dichromate is a chemical compound typically used as an inorganic chemical reagent for industrial and laboratory processes. This chemical is also used to produce shoe polishers, glues, paints and waxes. It is also commonly used in the laboratory as analytical reagent and potassium dichromate is also used in industry.

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 especially useful when looking for mahogany or wood floors or show their brighter colors.

Other uses of potassium dichromate include:

  • Leather tanning for footwear
  • Oxidizing agent in the photo printing process
  • Cleaning of glassware or engraving of glassware.


Potassium dichromate should be kept away from flammable material. Otherwise, you may have an explosive situation to cope with.

There is great debate about the real health hazards of potassium dichromate. This compound and all other dichromates are considered cancer causing agents or carcinogens by the National Institute of Occupational Safety and Health (NIOSH), a US federal agency that is responsible for research and recommendations for the prevention of work-related illness and injury.

However, the Office of Pesticide Programs of the United States Environmental Protection Agency has classified potassium dichromate as most likely non-carcinogenic to humans.

The compound can be easily dispersed through the air, making the risk of inhalation one of the greatest dangers associated with it. Prolonged exposure to the chemical by inhalation may cause asthma. The chemical is also corrosive to the eyes, skin and respiratory tract and may cause damage to the kidneys and liver if swallowed.

Ammonium dichromate

Molecular formula

(NH 4) 2 Cr 2 O 7 or Cr 2 H 8 N 2 O 7

Chemical names

Ammonium dichromate; Ammonium dichromate; 7789-09-5; Diammonium dichromate; Ammonium dichromate (VI); Ammonium dichromate (VI)


The ammonium dichromate is also a dichromic acid salt and is a bright red-orange crystalline solid. It easily ignites and burns producing a voluminous green residue. If heated in a closed container, the container may rupture due to decomposition of the material.

It can also act as a strong oxidizing agent if mixed. It is soluble in water and is odorless. Ammonium dichromate is a very strong oxidant which is frequently used for pyrotechnic compositions as a catalyst. It has also been commonly used in photography and lithography.

Ammonium dichromate is a good source of pure nitrogen in the laboratory and is used as a catalyst for the catalytic oxidation of ammonia. It is also used to fix dyes and in the manufacture of photosensitive films acting as photoactive.

Sodium dichromate

Molecular formula

Na2 Cr2 O7 or Cr2 Na2 O7

Chemical names

Sodium dichromate; Celcure; Sodium bichromate; Disodium dichromate; Sodium dichromate (VI)


Sodium dichromate is a crystalline, inorganic, orange to red compound that emits toxic fumes of chromium upon heating. Sodium chromate can be converted into a dichromate acid by a continuous process with sulfuric acid, carbon dioxide or a combination of these two.

Its molecular weight is 261,965 g / mol. It is highly corrosive and is a strong oxidizing agent. It is used primarily for the production of other chromium compounds and is also used in metal treatments, wood preservatives and as a corrosion inhibitor.


Sodium dichromate mainly affects the respiratory system, causing ulcerations, bronchitis, pneumonia and asthma as well as it can affect the gastrointestinal tract, liver, kidneys and immune system.

It is a carcinogen and is associated with risks of developing lung cancer and nasal cavity cancer. Sodium dichromate may be irritating to the skin, eyes and mucous membranes.


It is used as a corrosion inhibitor, and in the manufacture of other chemicals.

Health hazards of dichromic acids

Dichromatic acid is toxic by ingestion. Inhalation of dichromate acid powder is also toxic. Dichromatic acid exposed to fire may produce irritating, corrosive and / or toxic gases. Contact with the substance may cause severe burns to the skin and eyes.

Fire danger

Dichromatic acid speeds up burning when involved in a fire. May explode due to heat or contamination. They react explosively with hydrocarbons (fuels). It can ignite fuels (wood, paper, oil, clothing, etc.). Containers may explode when heated.

Other uses of dichromic acids

In addition to the uses of the ammonium, sodium and potassium dichromate discussed above, dichromic acids are used in chromium to protect metals from corrosion and to optimize paint adhesion.


  1. UK Laboratory Chemicals. (2015). Ammonium Dichromate. 24-12-2016, from Ammonium Dichromate Store Website: ammoniumdichromate.co.uk.
  2. National Center for Biotechnology Information. PubChem Compound Database; CID = 24600. Website: pubchem.ncbi.nlm.nih.gov.
  3. Reid. D.. (2003). Potassium Dichromate. 24-12-2016, from Study.com Website: study.com.
  4. ChemicalBook. (2016). Dichromic acid. 24-12-2016, from Chemical Land Website: chemicalbook.com
  5. Chemistry Web. (2016). Molar mass. 24-12-2016, from Quimicaweb.net Website: quimicaweb.net.
  6. NIOSH Education and Information Division. (2012). National Institute for Occupational Safety and Health (NIOSH). 24-12-2016, from NIOSH Web site: cdc.gov.