Ammonium dichromate

Ammonium dichromate is an orange crystalline salt with formula (NH₄)₂Cr₂O₇. It is a strong oxidizer used in chemical demonstrations and formerly in photographic processes.

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Ammonium dichromate volcano: A demonstration in which heated ammonium dichromate decomposes into green chromium(III) oxide, nitrogen, and water vapor. The classic demonstration uses the salt’s exothermic decomposition to produce an expanding mound of green solid.
Ammonium: The polyatomic cation NH₄⁺, formed when ammonia accepts a proton. Two ammonium ions balance the charge of each dichromate ion in the salt.
Photographic printing: The production of images on photosensitive materials through controlled exposure and chemical processing. Ammonium dichromate served as a light-sensitive ingredient in some historical printing processes.
Hexavalent chromium: Chromium in the +6 oxidation state, present in chromates and dichromates and associated with serious health hazards. The dichromate ion contains chromium(VI), which drives the salt’s major health risks.
Thermal decomposition: The breakdown of a chemical compound into simpler substances caused by heat. Heating initiates the salt’s breakdown into chromium(III) oxide, nitrogen, and water.
Dichromate: The polyatomic anion Cr₂O₇²⁻, containing two chromium atoms and seven oxygen atoms. This anion supplies the chromium and oxygen in ammonium dichromate.
Gum bichromate: A photographic printing process in which dichromate-sensitized gum hardens under light and holds pigment. Ammonium dichromate could sensitize the gum layer used to form the print.
Carcinogen: An agent capable of causing cancer in humans or other organisms. Chromium(VI) compounds are recognized carcinogenic hazards, making exposure prevention essential.
Oxidation–reduction reaction: A chemical reaction involving electron transfer and changes in oxidation states. Chromium is reduced while ammonium ions are oxidized during decomposition.
Ionic compound: A substance composed of positively and negatively charged ions held together by electrostatic attraction. Ammonium dichromate is an ionic solid made from ammonium and dichromate ions.