Potassium Chromate: Molecular Formula, Properties, and Uses

Potassium chromate is basically an inorganic compound with the chemical formula K₂CrO₄.

• It is a yellowish-colored substance which is naturally odorless.
• Potassium chromate is water-soluble.
• It naturally occurs from a mineral called Tarapacaite.
• Tarapacáite is the mineral form of potassium chromate.
• It forms bright yellow crystals.
• Potassium chromate compound is a known human cancer and has been related to an increased risk of developing sinonasal cavity lung cancer and cancer.
• When heated, it decomposes and releases toxic gases of potassium oxide.

Key Terms: Potassium chromate, Chemical compound, Organic compound, Inorganic compound, Dipotassium monochromator, Molecular formula, Atoms, Oxygen, Ions

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What is Potassium Chromate?

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Potassium chromate has the chemical formula K₂CrO₄ and is an inorganic compound.

• It is also known as a dipotassium monochromator or bipotassium chromate.
• It consists of chromate and potassium ions in a ratio of 1:2.
• K₂CrO₄ is among the most used laboratory chemicals or substances.
•  K₂CrO₄ has no smell with a bitter taste.
• When potassium chromate is heated it releases toxic chromium fumes.
• Potassium chromate appears as crystal solid and yellowish in color.
• This chemical analysis is the most used laboratory chemical and is used in making pigments for paints and inks, as a fungicide, and also to make chromium compounds,
• It can affect your throat, lungs, and nose, causing ulcerations, bronchitis, & cause shortness of breath, asthma, and pneumonia, when came into contact.

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Structure of  Potassium Chromate (K₂CrO₄)

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Potassium chromate or K₂CrO₄ consists of two positively charged potassium i.e., K⁺ ions, and one chromate i.e., CrO₄^2- ions.

• There is an ionic bond formed between potassium and chromate ions, that’s why it is known as an ionic compound.
• The chromate ion is made up of one chromium atom and four oxygen that have a tetrahedral structure.

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Properties of potassium Chromate (K₂CrO₄)

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The chemical and physical properties of  K₂CrO₄ or potassium chromate are as follows;

Some other properties of potassium chromate are described below.

• This compound appears like a crystal & has a yellowish color and is odorless.
• It is a potassium salt consisting of potassium and chromate ions in 2:1,
• It is highly soluble in water and insoluble in alcohol.
• The melting point of potassium chromate is approximately equal to 1241K and its boiling point is approximately equal to 1270K.
• K₂CrO₄ crystallizes in a rhombic lattice.

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How is Potassium Chromate Prepared?

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Potassium chromate or  K₂CrO₄ is prepared in labs by combining or infusing two or more chemical substances on a flame. It can be prepared using the following methods:

• By mixing potassium dichromate with potassium hydroxide,
• By mixing chromium oxide with potassium hydroxide
• By mixing sodium dichromate with potassium chloride

By mixing potassium dichromate with potassium hydroxide

When Pulverized potassium dichromate is dissolved in boiling water, & potassium carbonate dihydrate (K₂CO₃ · 2H₂O) is added while stirring. The reaction mixture obtained crystals of potassium chromate when filtered and dried.

The Chemical formula is:

K₂Cr₂O₇(aq) + 2KOH → 2 K₂CrO₄ + H₂O.

By mixing chromium oxide with potassium hydroxide

When potassium hydroxide and chromium oxide are mixed into each other, potassium chromate is obtained.

The Chemical formula is:

2KOH + Cr₂O₃ → 2 K₂CrO₄ + H₂O.

By mixing sodium dichromate with potassium chloride

When chromite ore and sodium carbonate are fused in the presence of air, Dichromates are usually prepared.

• The solution is further purified with sulphuric acid so that sodium dichromate (Na₂Cr2O₇.2H₂O) can be extracted.
• Now potassium dichromate can be obtained by reacting a solution of sodium dichromate with potassium chloride.

The Chemical formula is:

Na₂Cr₂O₇ + 2KCl →  K₂Cr₂O₇ + 2NaCl.

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Uses of Potassium Chromate

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Potassium chromate or  K₂CrO₄ is mainly used in chemical laboratories. Here are some other uses as well which are as follows;

• As an oxidizing agent; it is used as an oxidizing agent in organic synthesis.
• It is used in the qualitative inorganic analysis to detect the ions in aqueous solution.
• It is used in the manufacture of dyes. It is also used in making inks and pigments for paints.
• It is used in precipitation titrations as an indicator, as it turns red in the presence of excess silver ions.
• It is used in tanning leather and the textile dyeing process.
• It is used as a fungicide & also used in the leaching process.
• It is used in the production of several other chromium compounds.

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Potassium Chromate Indicator

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Potassium chromate is a metalochrome indicator.

• Mohr's method is based on the quantitative determination of chloride, bromide, and cyanide ions by titrating with a standard solution of silver nitrate and a few ml of potassium chromate as an indicator.
• The yellow-colored potassium chromate solution turns to a brick-red precipitate of silver chromate at the equivalence point. 
• When potassium chromate is used as an indicator, after the chloride ions have been removed, silver ions react with chromate ions, and the solubility product of silver chromate is exceeded, resulting in the formation of a reddish-brown precipitate. 
• Precipitation titration involves placing a known amount of halide solution in a conical flask, adding 1-2 ml of potassium chromate indicator, and titrating it against a standard solution of silver nitrate in the burette.
• With the first drop of extra silver nitrate applied, the indicator creates a red-colored precipitate of silver chromate.

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Things to Remember

• Potassium chromate is an inorganic compound.
• The chemical formula of Potassium chromate is K₂CrO₄.
• Potassium chromate is carcinogenic, which means it has the potential to cause cancer.
• Potassium chromate is a metalochrome indicator.
• Potassium chromate or K₂CrO₄ consists of two positively charged potassium i.e., K⁺ ions, and one chromate i.e., CrO₄^2- ions.
• The density of Potassium chromate is 2.7320 g/cm³.
• It is also corrosive and may cause eye damage or blindness if exposed,
• It may also be a cause of impaired fertility and heritable genetic damage.
• It can also harm the unborn children in the mother's womb.

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