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Ammonium dichromate is a flammable inorganic compound with the chemical formula (NH4)2Cr2O7. It is produced in the form of orange-red needles during crystallisation. Ammonium dichromate is a hazardous salt used to make organic emulsions like gelatin more susceptible to the hardening effects of actinic light.
- Ammonium dichromate is readily ignited and leaves a large green residue when burned.
- It is highly light-sensitive.
- When heated in a closed container, ammonium dichromate may explode owing to material degradation.
- The IUPAC name of the compound is diammonium oxido-(oxido-dioxo-chromio)oxy-dioxo-chromium.
- It is also known as Vesuvian Fire, as it looks the same as volcanoes.
- Ammonium dichromate is highly carcinogenic in nature.
Read More: Ammonium Nitrate
Key Terms: Ammonium Dichromate, Inorganic Compounds, Orange Red Crystals, Residue, Crystallisation, Oxidising agent, Contaminated, Flammable Materials
What is Ammonium Dichromate?
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Ammonium dichromate is an inorganic compound that consists of salts of ammonium ions and dichromate ions. It is commonly referred to as hexavalent chromium as the oxidation state of chromium is six. However, due to the carcinogenic nature of the substance, this display proved controversial in schools.
- Ammonium Dichromate is a toxic salt that is used to sensitize organic emulsions such as gelatin.
- It was also employed in pyrotechnics and photography's early days.
- It may also be used as an oxidizing agent when combined with or contaminated with flammable materials.
- Other name of Ammonium Dichromate is Ammonium Bichromate.
Ammonium Dichromate
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Ammonium Dichromate Structure
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The molecular formula of the ammonium dichromate is (NH4)2Cr2O7. Its structure is given in the image provided below.
Ammonium Dichromate Structure
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General Properties of Ammonium Dichromate
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The general properties of ammonium dichromate are provided in the table below:
| Category | Data |
|---|---|
| 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 |
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Physical Properties
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The physical properties of ammonium dichromate are as follows:
- Ammonium dichromate is an odourless compound
- It is the form of Orange-red crystals
- Ammonium dichromate is soluble in water and alcohol at room temperature.
- It is insoluble in acetone.
- Ammonium dichromate is a stable compound under standard temperature and pressure.
Read also: Dalton’s atomic theory
Chemical Properties
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Ammonium dichromate decomposes when heated, resulting in the creation of chromium (III) oxide and nitrogen gas.
(NH4)2Cr2O7(s) → Cr2O3(s) + N2(g) + 4H2O(g)
Read More: Synthetic Polymers
Uses of Ammonium Dichromate
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The various uses of ammonium dichromate are as follows:
- Ammonium Dichromate include pyrotechnics and lithography as a source of pure nitrogen in science labs, and as a catalyst.
- It's also employed in the production of alizarin, chrome alum, leather tanning.
- The compound is used in the oil purification as a mordant for colouring colours.
- It's an authorised insecticide that's also used as a dye mordant and a pigment.
Read More: Critical temperature
Hazards and Safety Measures
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The following are the main hazards of ammonium dichromate:
- Ammonium Dichromate is a dangerous, very poisonous compound.
- The compound is carcinogenic and mutagen in nature.
- It is highly oxidising, and environmentally hazardous.
- Ammonium dichromate, like other chromium (VI) compounds, is very poisonous and, in certain cases, explosive.
- It cause skin irritation.
To deal with these dangers, one must adhere to safety precautions. When utilising ammonium dichromate, precautions must be followed. Avoid physical contact with ammonium dichromate by using eye protection (wear gloves).
Things to Remember
- Ammonium dichromate is an extremely dangerous compound.
- The compound is also known as a carcinogen that is identical to all chromium (VI) compounds.
- Furthermore, it is a severe irritant at the same time.
- When heated in a closed container, ammonium dichromate may explode owing to material degradation.
- It can also be used as an oxidising agent when combined with or contaminated with flammable materials.
- The remaining ammonium dichromate produces a yellow or orange colour solution when the dark green colour powder is mixed with water.
Sample Questions
Ques. What Happens When Ammonium Dichromate is Heated? (5 marks)
Ans. 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.
Ques. What are The Uses of Ammonium Dichromate? (3 marks)
Ans. Ammonium dichromate has long been used in pyrotechnics, as well as in the early days of photography and lithography, as a source of pure nitrogen in the laboratory, and as a catalyst. It’s also used in the production of alizarin, chrome alum, leather tanning, and oil purification as a mordant for colouring colours. In the manufacture of the phosphor raster of TV screens, LCDs, and many other devices, photosensitive films comprising PVA, ammonium dichromate, and a phosphor are spin-coated as liquid slurries. The ammonium dichromate, on the other hand, also serves as a photoactive site. It's also an authorised insecticide that's also used as a dye mordant and a pigment.
Ques. What happens when ammonium dichromate is heated? (2 marks)
Ans. 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.
- It is an Odourless compound
- It is the form of Orange-red crystals
Ques. Is ammonium dichromate ionic or covalent? (2 marks)
Ans. Because the ammonium cation and the dichromate anion have an ionic link, the ammonium dichromate molecule can be called an ionic compound. Covalent bonds, on the other hand, hold the polyatomic cation and anion together.
Ques. Why does baking soda smell like ammonia? (2 marks)
Ans. Ammonium dichromate is a hazardous and toxic salt used to make organic emulsions like gelatin more susceptible to the hardening effects of actinic light. Baking soda reacts like an acid, forming small quantities of sodium ammonium carbonate. Ammonia is created when baking soda is mixed with an ammonium salt and water.
Ques. What is the oxidation state for Cr in (NH4)2Cr2O7? (1 mark)
Ans. The oxidation number of the chromium i.e. Cr in (NH4)2Cr2O7 is +6.
Ques. What is obtained when ammonium dichromate is heated? (3 marks)
Ans. The chemical ammonium dichromate is made up of ammonia and chromate. In this molecule, chromate has an oxidation number of +6. When ammonium dichromate is heated, we must now write the equation. The following is the reaction: N2 + 4H2O + Cr2O3 (NH4)2Cr2O7. We may deduce from the balanced chemical reaction of ammonium dichromate on heating that ammonium dichromate yields nitrogen gas.
Ques. Explain catalyst? (2 marks)
Ans. The catalyst, as the name suggests, is used in the chemical reaction to increase the rate of a chemical reaction when any suitable substance is added to it. It is divided into two categories of: homogeneous and heterogeneous catalysts. The chemical equation illustrating the effect of the catalyst is as follows:
- Decomposition of hydrogen peroxide into water and oxygen: 2 H2O2 → 2 H2O + O2
Ques. What is the difference between baking soda and baking powder? (4 marks)
Ans. The difference between baking soda and baking powder are as follows:
| Baking Soda | Baking Powder |
|---|---|
| It is made of only one ingredient namely sodium bicarbonate. | It is made of multiple ingredient namely bicarbonate and its substituent salts. |
| Baking soda react with acids. | Baking Powder does not react with acid. |
| It is a short leavening process. | It is a long leavening process. |
| The end product created with baking soda are not fluffy. | The end product created with baking powder are fluffy. |
Ques. Explain (A) Mordant
(B) Chrome Alum
(C) Lithography (3 marks)
Ans. (A) Mordant: Mordant, also known as dye fixative, is a substance that is used for dyeing clothes and fabrics. It forms a complex coordinated compound that gets attached to tissues.
(B) Chrome Alum: Chrome Alum or Alum is defined as the hydrated mixture of double sulphate salt of aluminium. In the field of medicine, it is also called aluminium hydroxide, is used in vaccine adjuvants.
(C) Lithography: Lithography is a process of printing original planographic images on the immiscibility of oil and water. It is a form of chemical process in which an image is created on the end product.
Ques. What is the value of oxidation for sulfur in sulphuric acid (H2SO4)? (1 mark)
Ans. The required oxidation number of the sulfur in sulphuric acid (H2SO4) is +6.
Ques. What is the difference between oxidation state and oxidation number? (4 marks)
Ans. The difference between oxidation state and oxidation are as follows:
| Oxidation State | Oxidation Number |
|---|---|
| Oxiation state is applied on any compounds or elements. | Oxidation number is applied on the coordinated compounds. |
| The required state represent charge of the central atom. | The required state rdoes not epresent charge of the central atom. |
| It is represented by arabic numerals. | It is represented by roman numerals. |
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