Chromic Acid - H2CrO4

What is Chromic acid?

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

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

Chromic acid H2CrO4
Molecular Weight of Chromic acid 118.008 g/mol
Density of Chromic acid 1.201 g/cm3
Melting Point of Chromic acid 197 °C
Boiling Point of Chromic acid 250 °C

Structure of Chromic acid (H2CrO4)

 

Structure of Chromic acid

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, 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 can behave the same exact way. However, the caveat to this argument is that no more than a ketone will oxidise a secondary ketone and dichromic acid will only oxidise the aldehyde. For the first step of the mechanism, the aldehyde would be oxidised to a ketone and oxidised to a carboxylic acid again, subject to no major steric hindrance impeding this reaction.

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.
Chromium trioxide and pyridinium chloride produce pyridinium chlorochromate. This reagent converts to the corresponding aldehydes (R-CHO) primary alcohols.

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?

First, sodium dichromate, or potassium dichromate, must be  combined with a little water to produce a paste. While applying sulphuric acid to the paste and continuously mixing, chromic acid is formed.

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.

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