Ammonium Dichromate - (NH4)2Cr2O7

What is Ammonium Dichromate?

Ammonium dichromate is a flammable inorganic compound with the chemical formula (NH4)2Cr2O7. It is orange-red needles produced during crystallization. A toxic chemical salt used to sensitize organic emulsions such ad gelatin to the hardening effect of actinic light. It is more sensitive to light.

IUPAC name – diammonium oxido-(oxido-dioxo-chromio)oxy-dioxo-chromium

H8Cr2N2O7 Ammonium Dichromate
Density 2.12 g/cm³
Molecular Weight/ Molar Mass 252.07 g/mol
Autoignition temperature 190 °C
Melting point 180 °C
Chemical Formula (NH4)2Cr2O7

Ammonium Dichromate Structure – (NH4)2Cr2O7

Ammonium Dichromate

Physical Properties of Ammonium Dichromate – (NH4)2Cr2O7

Odour Odourless
Appearance Orange-red crystals
Stability Stable under recommended storage conditions
Specific Gravity 2.1500
Solubility Insoluble in acetone; soluble in alcohol

Chemical Properties of Ammonium Dichromate – (NH4)2Cr2O7

    • On heating, Ammonium dichromate undergoes decomposition resulting in the formation of chromium(III) oxide and nitrogen gas.

(NH4)2Cr2O7(s) → Cr2O3(s) + N2(g) + 4H2O(g)

Uses of Ammonium Dichromate – (NH4)2Cr2O7

  • Ammonium dichromate is used in sensitizing solutions used in lithography.
  • Used in pyrotechnics, lithography and photoengraving. It is also used as a magnetic recording material.
  • It is used as an approved pesticide and used as a mordant for dyeing, used as a pigment.

Frequently Asked Questions

What are the uses of ammonium dichromate?

Ammonium dichromate has been used as a source of pure nitrogen in the laboratory and also as a catalyst in pyrotechnics. This compound also played an important role In the early days of photography as well as in lithography. It is also used in the manufacture of alizarin, chromium alum, leather tanning, and oil purification as a mordant for dyeing pigments.

What happens when ammonium dichromate is heated?

Upon heating, ammonium dichromate decomposes to create nitrogen dioxide, water vapour (Water is gaseous in this reaction due to the relatively high reaction temperature), and solid chromium (III) oxide.

Is ammonium dichromate ionic or covalent?

The ammonium dichromate molecule can be considered as an ionic compound because it features an ionic bond between the ammonium cation and the dichromate anion. However, the individual polyatomic cation and anion are held together by covalent bonds.


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