Chromic Acid - H₂CrO₄

What is Chromic acid?

Chromic Acid is a naturally occurring oxide with the formula H₂CrO₄.

Table of Contents

• Properties of Chromic acid
• Structure of Chromic acid
• Uses of Chromic Acid
• Health Hazards
• Frequently Asked Questions

Chromic Acid is also called Tetraoxochromic acid or Chromic(VI) acid. It is usually a mixture made by adding concentrated sulphuric acid (H₂SO₄) to a dichromate which consists of a variety of compounds and solid chromium trioxide.

• Molecular chromic acid – H₂CrO₄ is similar to sulphuric acid (H₂SO₄) as both are strong acids, however, only the first proton is lost easily.
• Dichromic acid – H₂Cr₂O₇ is the fully protonated form of the dichromate (Cr²O₇^–) ion. Also, it is seen as the product of adding chromium trioxide (CrO₃) to molecular chromic acid.

Properties of Chromic acid – H₂CrO₄

Structure of Chromic acid (H₂CrO₄)

Structure of Chromic acid – H2CrO4

Uses of Chromic acid (H₂CrO₄)

• Chromic acid acts as an intermediate in chromium plating.
• It is used in ceramic glazes and coloured glass.
• Chromosulfuric acid or sulfochromic mixture is a strong oxidizing agent that is used to clean laboratory glassware.
• It has the ability to brighten raw brass and therefore it is used in the instrument repair industry.
• In the year 1940, it was used in hair dye.

The completely protonated form of the dichromate ion is dichromic acid, H2Cr2O7 and can also be seen as the result of adding chromium trioxide to molecular chromic acid. When reacting with an aldehyde or ketone, dichromic acid exactly the same way. In organic chemistry, the chromic acid solution can oxidize primary alcohols to aldehyde and secondary alcohol to a ketone. but the tertiary alcohols and ketones are unaffected . During oxidation, the colour of chromic acid changes from orange to brownish green.

Chromic acid is capable of oxidising many forms of organic compounds, and many variants have been created for this reagent. Chromic acid is referred to as the Jones reagent in aqueous sulfuric acid and acetone, which oxidises primary and secondary alcohols into carboxylic acids and ketones, respectively, though rarely affecting unsaturated bonds. Cromyl chloride which is used to test the presence of chloride ions in inorganic chemistry, is derived from chromic acid.
Chromium trioxide and pyridinium chloride produce pyridinium chlorochromate. This reagent converts to the corresponding aldehydes (R-CHO) primary alcohols. Chromic acid was  used to repair musical instruments due to its ability to “brighten” raw brass.

Health hazards

Hexavalent chromium compounds such as chromium trioxide, chromates, chromic acids, and chlorochromate are toxic and carcinogenic. Therefore, chromic acid oxidation is used only in the aerospace industry and not on any other industrial scale.

Chromic acids are strong oxidizers and can react violently if mixed with some easily oxidizable organic substances which can cause explosions or fires. In case of any burns caused by this acid, it is treated with a dilute solution of sodium thiosulfate.

Frequently Asked Questions

What are the uses of chromic acid?

This compound is widely used as an intermediate in chromium plating. Chromic acid is also used in coloured glass and ceramic glazes. In the 1940s, this compound was an integral part of several hair dyes.

How can chromic acid be prepared?

Sodium or potassium dichromate is made as a paste with little water. Sulphuric acid is added in drops to this paste and continuously mixed to get chromic acid.

Which neutralizing agents are ideal for neutralizing chromic acid?

Chromic acid must be diluted in a good amount of water first. Then, it can be neutralized with a reductant after the dilution process. Some excellent neutralizing agents are sodium/potassium metabisulfite, sodium thiosulfate, or sodium sulfite.

Learn more about the physical and chemical properties of Chromic acid (H₂CrO₄) from the experts at BYJU’S.