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Chromic Acid

Chromic Acid is the mixture of concentrated sulfuric acid and a dichromate ion, which may contain a variety of compounds. It is also known as Tetraoxochromic acid or Chromic(VI) acid. 

More About Chromic Acid

There are two forms of chromic acids:

  • Molecular Chromic Acid (H2CrO4): Similar to H2SO4.
  • Dichromic Acid (H2Cr2O7): A fully protonated form of the dichromate ion(Cr2O7).

Following are the properties of the chemical

Chemical FormulaH2CrO4 or H2Cr2O7 
Molecular Weight 118.008 g/mol
Density 1.201 g/cm3
Melting Point197℃
Boiling Point250℃

Chromic acid structure
Chromic acid structure (Source)

Chromic Acid Test for Alcohols and Aldehydes

Now, let’s have a look at this test for alcohols and aldehydes which involves this chemical (Oxidation Mechanism)

Procedure:

Three drops of the unknown compound to be tested are mixed with 5 drops of acetone and 5 drops of tetraoxochromic acid solution.

Result:

The formation of a bluish-green colour of the Cr(III) ion indicates a positive test. If the unknown compound is insoluble in water, two layers are present. A bluish-green colour in either layer indicates a positive test.

Reactions:

Aldehydes and primary alcohols are oxidized to carboxylic acids while the Cr+6 ion in the tetraoxochromic acid is reduced to Cr+3 ion.

Secondary alcohols are oxidized to ketones while the Cr+6 ion in the tetraoxochromic acid is reduced to Cr+3 ion.

Applications of Chromic Acid

  • Used in chromium plating.
  • Used in ceramic glazes and colored glass.
  • Can be used to clean laboratory glassware.
  • Used in hair dye.

FAQs

What is the formula for chromic acid?

The formula is H2CrO4(molecular form) and H2Cr2O7(dichromic form).

What is chromic acid?

It is the mixture of a concentrated sulfuric acid and dichromate ion.

How is chromic acid prepared?

Sodium dichromate or potassium dichromate must be first combined with water to produce a paste. Continuous addition of concentrated sulfuric acid and mixing produces tetraoxochromic acid.

More on Inorganic Compounds

Copper Hydroxide (Cu(OH)2)Hydrosulfuric Acid (H2S)
Chlorine Trifluoride (ClF3)Barium Carbonate (BaCO3)
Sodium Sulfate (Na2SO4)Ammonium Persulfate ((NH4)2S2O8)

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