Question

Ammonium dichromate is used in some fire works. The green coloured powder blown in the air is (a) \(\mathrm{CrO}_{3}\) (b) \(\mathrm{Cr}_{2} \mathrm{O}_{3}\) (c) \(\mathrm{Cr}\) (d) \(\mathrm{CrO}\left(\mathrm{O}_{2}\right)\)

Short answer

The green powder is (b) \\( ext{Cr}_2 ext{O}_3 \\).

Step-by-step solution

Understand the Reaction

Ammonium dichromate ( ext{(NH}_4 ext{)}_2 ext{Cr}_2 ext{O}_7) decomposes when heated. The reaction generates nitrogen gas ( ext{N}_2), water vapor ( ext{H}_2 ext{O}), and chromium(III) oxide ( ext{Cr}_2 ext{O}_3). This green-colored powder is what is observed in the air during fireworks.

Recall the Color

Chromium(III) oxide ( ext{Cr}_2 ext{O}_3) is known for its distinctive green color. This is relevant because we are looking for the identity of the green powder produced in the reaction.

Match Options to Reaction Products

Given the reaction products, identify the correct chemical formula that matches the green powder with the available options. The only product from the decomposition of ammonium dichromate corresponding to the green powder is chromium(III) oxide, which is ext{Cr}_2 ext{O}_3.

Key concepts

Chromium(III) Oxide

Chromium(III) oxide, with the chemical formula \( \mathrm{Cr}_2 \mathrm{O}_3 \), is a fascinating compound because of its distinctive green color. This oxide is one of the principal oxides of chromium and is often used in various applications, including as a pigment called "chrome green." In the decomposition of ammonium dichromate, \( \mathrm{Cr}_2 \mathrm{O}_3 \) appears as a powdery substance due to its formation during the breakdown of the compound. When ammonium dichromate is heated, it breaks down to release nitrogen gas, water vapor, and this shiny green powder, \( \mathrm{Cr}_2 \mathrm{O}_3 \), which you might notice because of its vivid color.
\( \mathrm{Cr}_2 \mathrm{O}_3 \)'s green hue is not only used in fireworks displays but also in ceramics, paints, and even in the coating of metals to prevent corrosion. This chemical property aligns well with its use in various industrial processes, making it a versatile compound with practical applications.

Chemical Reactions

Chemical reactions involve the transformation of one or more substances into new products. In the case of ammonium dichromate decomposition, it's a thermally-induced chemical reaction where heating the substance leads to its decomposition. When \( \mathrm{(NH}_4 \mathrm{)}_2 \mathrm{Cr}_2 \mathrm{O}_7 \) is heated, it decomposes explosively, transforming into chromium(III) oxide, nitrogen gas, and water vapor. The balanced chemical equation for this reaction is:
\[ \mathrm{(NH}_4 \mathrm{)}_2 \mathrm{Cr}_2 \mathrm{O}_7 \rightarrow \mathrm{Cr}_2 \mathrm{O}_3 + 4 \mathrm{H}_2 \mathrm{O} + \mathrm{N}_2 \]
This decomposition reaction is an example of a redox reaction, where oxidation and reduction occur simultaneously. The ammonium ion \( \mathrm{(NH}_4^+) \) provides the reducing condition, while the dichromate ion \( \mathrm{Cr}_2\mathrm{O}_7^{2-} \) acts as the oxidizing agent.
Such reactions not only produce expected products but also energy, often observed as changes in heat or light. Explaining these changes helps us understand the dynamics and energetic considerations of chemical reactions, vital for fields ranging from chemistry labs to industrial applications.

Fireworks Chemistry

Fireworks displays captivate us with their vibrant colors and dramatic effects. This magic in the sky is all about chemistry, and substances like ammonium dichromate play a role in creating these spectacular visuals. The decomposition of ammonium dichromate provides a fascinating example of how chemical reactions are harnessed in fireworks.
The characteristic green seen during some fireworks displays is due to \( \mathrm{Cr}_2 \mathrm{O}_3 \), the beautiful green oxide of chromium formed when ammonium dichromate decomposes. Fireworks rely on a delicate balance of chemicals that burn at varying temperatures to create different colors and effects. By controlling the compound mixture and their reactions, firework manufacturers can produce specific colors and patterns.
Chemicals in fireworks, like metals and metal salts, combust to produce different colors. For example, strontium gives red, barium produces green, and copper yields blue. Therefore, understanding the chemistry of compounds like ammonium dichromate is essential in the design and execution of fireworks displays, illustrating the intersection of art and science.