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What is Ammonium Dichromate?
Ammonium dichromate is a flammable inorganic compound with the chemical formula (NH4)2Cr2O7.
Ammonium dichromate is orange-red needles produced during crystallization. A toxic chemical salt is 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
Ammonium Dichromate Structure – (NH4)2Cr2O7
General Properties of Ammonium Dichromate – (NH4)2Cr2O7
| 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 |
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.
Reactions
The volcano demonstration includes the igniting of a pile of the salt and this initiates the following exothermic conversion:
(NH4)2Cr2O7 (s) → Cr2O3 (s) + N2 (g) + 4 H2O (g) (ΔH = −429.1 ± 3 kcal/mol)
Like the ammonium nitrate, it is also thermodynamically unstable. Its decomposition reaction proceeds to the process of completion once we initiate it, producing voluminous powder of chromium (III) oxide that is dark green in color.
Not all of the ammonium dichromate decomposes in this specific reaction. When the dark green color powder mixes up in the water then, as a result, a yellow or an orange color solution is the outcome we get from the leftover ammonium dichromate.
Safety
The Ammonium dichromate is similar to all the chromium (VI) compounds and it is highly toxic and also a proven carcinogen. Moreover, it is also a strong irritant at the same time.
Incidents
In the airtight and sealed containers, ammonium dichromate may explode if provided excess heat. In the year 1986, 2 workers lost their lives and 14 others were injured at the Diamond Shamrock Chemicals in Ashtabula, Ohio when about 2,000 lbs. of ammonium dichromate exploded because it was being dried in a heater.
Solved Example on Ammonium Dichromate Formula
Question: What is the oxidation state for Cr in (NH4)2Cr2O7?
Solution: The oxidation number of the chromium i.e. Cr in (NH4)2Cr2O7 is +6.
Frequently Asked Questions – FAQs
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 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.
Is ammonia bicarbonate baking soda?
NH4HCO3, or ammonium bicarbonate, is a typical leavening agent that produces carbon dioxide without the use of an acid. It doesn’t have the alkaline flavour of baking powder or soda.
Why does baking soda smell like ammonia?
Baking soda will react like an acid, resulting in the formation of tiny amounts of sodium ammonium carbonate. When baking soda is combined with an ammonium salt and water, ammonia is produced.
How Do You Define The Terminology Ammonium Dichromate(NH4)2Cr2O7?
Ammonium dichromate is an inorganic compound with the chemical formula (NH4)2Cr2O7. It is orange-red needles produced during crystallization.
Ammonium dichromate is a salt consisting of ammonium ions and dichromate ions, a toxic chemical salt used to sensitize organic emulsion. It is more sensitive to light. It is readily ignited and burns to leave a sizable green residue. If ammonium dichromate is heated in a closed container, it may rupture due to the decomposition of the material. It also acts as a reliable oxidizing agent mixed with or contaminated with combustible material.
The following figure highlights a few of the things about Ammonium dichromate:
Because of its application in demonstrations of tabletop “volcanoes”, Ammonium dichromate is sometimes also termed as Vesuvian Fire. However, in schools, this demonstration became unpopular due to the compound’s carcinogenic nature. It has also been used in pyrotechnics and the early days of photography.
A glimpse, let’s have a look to the names of Ammonium dichromate:
IUPAC name – diammonium oxido-(oxido-dioxo-chromio) oxy-dioxo-chromium,
Other names – Ammonium bichromate
Ammonium pyrochromate, Chromic acid, diammonium salt; diammonium dichromate; Ammonium bichromate; Ammonium pyrochromate.
The following points and table give a depth-understanding of the various features or characteristics of Ammonium dichromate. These are as follows:
- The density of ammonium dichromate is 2.12g/cm 3
- It has a melting point of 180°c
- Exact molecular mass – 251.924166
- Ammonium dichromate is an explosive compound.
- The action makes chromic acid on ammonium hydroxide with subsequent crystallization.
What Happens When Ammonium Dichromate is Heated?
When it is heated, Ammonium dichromate (NH4)2Cr2O7 decomposes to produce chromium (III) oxide Cr2O3, nitrogen gas, and water vapor:
(NH4)2Cr2O7 (s) → Cr2O3 (s) + N2 (g) + 4H2O (g)
This reaction is based on a standard demonstration known as the “ammonium dichromate volcano.”
Orange-red color crystalline solid on intense heating swells up & decomposes violently with flashes of light. Greenish residue also gives steamy dunes, which condenses cooler parts of the test tube to form tiny droplets of water.
(Water is gaseous in this reaction due to the relatively high reaction temperature), and stable chromium (III) oxide.
As compared to the original ammonium dichromate, chromium (III) oxide crystals are “fluffier.”
Much of the mass of the starting material getaway as nitrogen gas and water vapor, the result looks like a much more significant amount of substance.
What are The Uses of Ammonium Dichromate?
Ammonium dichromate has been used in pyrotechnics and also plays an essential role in the early days of photography as well as in lithography, as a source of pure nitrogen in the laboratory, and as a catalyst.
It is also used as a mordant for dyeing pigments, in the manufacturing of alizarin, chrome alum, leather tanning, and oil purification.
Photosensitive films containing PVA, ammonium dichromate, and a phosphor are spin-coated as liquid slurries in the production of the phosphor raster of the TV screens, LCDs, and many other different devices. On the other hand, the ammonium dichromate acts as the photoactive site as well.
WHERE IS AMMONIUM DICHROMATE USED?
Ammonium dichromate is used in the production of dyes, inks, and pigments, as a wood preservative, and as a mordant in dyeing and printing textiles. It is also used in the production of fireworks and in the laboratory as an oxidizing agent.
HOW IS AMMONIUM DICHROMATE USED IN THE FOOD INDUSTRY?
Ammonium dichromate is not used in the food industry.
BENEFIT FOR AMMONIUM DICHROMATE HEALTH?
Ammonium dichromate does not have any known benefits for health.
WHAT ARE THE DANGERS OF AMMONIUM DICHROMATE?
Ammonium dichromate is a toxic and corrosive chemical that can cause skin and eye irritation, as well as respiratory problems if inhaled. It is also a strong oxidizing agent and can cause fires if it comes into contact with combustible materials.
HOW IS AMMONIUM DICHROMATE REGULATED ACROSS THE WORLD?
Ammonium dichromate is regulated differently across the world. In the United States, it is regulated by the Environmental Protection Agency (EPA) as a hazardous air pollutant. In the European Union, it is regulated under the REACH Regulation as a substance of very high concern. In Canada, it is regulated under the Canadian Environmental Protection Act, 1999.
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