Chromate Formula - Structure, Properties, Uses, Sample Questions

Chromate compound consists of elements Chromium & Oxygen. Chromium is a steely-grey, hard, brittle, and lustrous transition metal. Its atomic number is 24 and is represented by the symbol Cr. It is used mostly in alloys to increase strength and corrosive resistance. Oxygen is a highly reactive nonmetal and oxidizing agent that forms oxides with many elements/compounds. Its atomic number is 8 and is represented by the symbol O. Oxygen is a member of the chalcogen group in the periodic table.

Chromate Formula

Chromate is the salt of chromic acids that contains chromate anion. It is a chromium oxo anion & a divalent inorganic anion generated by removing two protons from chromic acid. Its chemical formula is CrO₄^2-. It is one of the numerous polyatomic ions which are used to create insoluble salts. Some of the chromate salts are sodium salts and potassium salts. Chromate is a powerful oxidizing agent and usually has an intense yellow color.

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Physical properties of Chromate

Appearance	Yellow powder
Odor	Odorless
Molecular Weight	115.9921 g/mol
Solubility	Insoluble in water
Valency	2

Chemical properties of Chromate

• Chromate ion acts as a strong oxidizing agent in acid solution. In alkaline solution chromate ion combined with water to form chromium(III) hydroxide.

CrO₄^2- + 4H₂O + 3e^- ⇢ Cr(OH)₃ + 5OH^-

• Chromate as its potassium salt reacts with barium nitrate to form barium chromate and potassium nitrate and vice versa.

K₂CrO₄ + Ba(NO₃)₂ ⇠⇢ BaCrO₄ + 2KNO₃

• Chromate reacts with hydrogen peroxide to produce a compound in which one or more oxygen atoms are replaced by peroxide.

Applications of Chromate

1. Sodium and potassium salts of chromate are used in enamels, finishing leather, and metal rust proofing due to their highly corrosive nature.
2. Potassium Chromate crystals are used as pigments in inks and dyes. It is poisonous/toxic if eaten.
3. Chromate is used in chrome plating to get rid of corrosion.
4. Lead Chromate is used in making industrial crayons which is not safe.

Sample Questions

Question 1: How can we distinguish the compounds Chromate & Dichromate?

Answer:

The compounds can be distinguished by their appearance. Chromate appears in bright yellow and where as Dichromate appears in orange color.

Question 2: Is Chromate acid or base?

Answer:

Chromate is a base because chromate ion is predominant species in alkaline solution. Where as Dichromate is acidic because it was the predominant species in acidic solution.

Question 3: Why Potassium Chromate is in yellow color?

Answer:

Initially Potassium Chromate is orange in color but it turns out into yellow when sodium hydroxide is introduced. It replaces the hydrogen ions from the solution.

Question 4: Where Potassium Chromate is used?

Answer:

Potassium Chromate is used as pigment in making paints, inks. It is also used as fungicide in chemical processing. It is carcinogenic and an oxidizing agent.

Question 5: Is Chromium and Chromate are different?

Answer:

Yes. They both are different. Chromium is an item that is applied as an electroplated finish. At the other hand Chromate characterize the process resistant to corrosion which is known as conversion finish.

Question 6: What are the minerals of chromate?

Answer:

Minerals containing chromium element are not common very few are present. The most common one is crocoite. It occurs as magnificent long red crystals. It's chemical formula is PbCrO₄. Rarely potassium chromate minerals are founded in Atacama desert. Finally the only known dichromate mineral is Lopezite.

Question 7: Calculate the molecular weight of CrO₄^-2?

Answer:

Molecular weight of Chromium (Cr) = 51.9961

Molecular weight of Oxygen (O) = 15.999

There are 1 Chromium 4 Oxygen atoms in Chromate compound

Total molecular weight = 51.9961 + (4 × 15.999)

= 51.9961 + 63.996

= 115.9921

Molecular weight of CrO₄^-2 is 115.9921 g/mol