Problem 54 - A Complete Resource Book in Chemistry for JEE Main

Question

The composition of golden spangles is (a) \(\mathrm{PbI}_{2}\) (b) \(\mathrm{BaCrO}_{4}\) (c) \(\mathrm{As}_{2} \mathrm{~S}_{3}\) (d) \(\mathrm{PbCrO}_{4}\)

Step-by-Step Solution

Answer

The composition of golden spangles is 9PbCrO4913 (lead(II) chromate).

Step 1: Understand the Composition of Golden Spangles

Golden spangles are commonly associated with their distinctive appearance and chemical composition. Recognize that golden spangles refer to a compound that has a characteristic golden or yellowish appearance.

Step 2: Identify Common Compounds with a Golden Appearance

Compounds that are known for their golden or yellow color often include lead and chromium compounds. Specifically, lead chromate (9PbCrO4913) is known for its bright yellow (golden) color and is commonly used in paints and pigments.

Step 3: Evaluate the Options Provided

Review the given options: (a) 9PbI2913 - Lead(II) iodide, which is yellow in color. (b) 9BaCrO4913 - Barium chromate, usually yellow. (c) 9As2S3913 - Arsenic sulfide, also known as orpiment, which is bright yellow. (d) 9PbCrO4913 - Lead(II) chromate, known for its bright yellow or golden appearance.

Step 4: Determine the Correct Answer

Identify which of these compounds is commonly referred to as 'golden spangles'. Given its bright yellow color and historical usage as a pigment, 9PbCrO4913 (Lead(II) chromate) is likely the answer.

Key Concepts

Lead Chromate

Lead chromate, symbolized as \( \mathrm{PbCrO}_{4} \), is a vibrant yellow inorganic compound. It has had a historical significance due to its extensive usage in paints and pigments. This compound stands out because of its rich, golden-yellow color. It has been popular in artistic applications for adding colors to paintings and even in industrial coatings.
Lead chromate forms as a precipitate when solutions of lead(II) acetate and potassium chromate react. Despite its beauty, one must be cautious as it contains lead, a heavy metal that poses health risks if handled improperly. Nevertheless, its chemical composition and properties have made it a subject of interest both in academic and industrial circles.

Golden Spangles

Golden spangles refer to materials or compounds that exhibit a distinctive golden or yellowish tone. These spangles evoke images of glimmering metals, yet they often pertain to chemical compounds like lead chromate due to their color.
In the context of the original exercise, golden spangles relate particularly to lead chromate, thanks to its glittering yellow appearance. The unique light-reflecting properties of these compounds give them a spangled effect, making them crucial in applications that require aesthetic appeal, such as decorative finishes or historical paintings.

Chemical Identification

Chemical identification is the process of determining a substance's chemical nature. This involves recognizing key properties such as color, composition, and reactions it undergoes. Identifying the correct compound relies on understanding these properties.
For instance, in determining whether a compound is lead chromate, one would observe its yellow color, typical of chromate compounds that interact with lead components. Also, the compound’s response to specific chemical tests, where it forms precipitates or changes color, aids in clinching its identification.

Compound Colors

The color of a chemical compound is related to its interaction with light. This results from the electronic transitions in the atoms or ions involved. When these atoms absorb certain wavelengths of light and reflect others, we perceive this as color.
In our scenario, compounds such as \( \mathrm{PbCrO}_{4} \), \( \mathrm{PbI}_{2} \), \( \mathrm{BaCrO}_{4} \), and \( \mathrm{As}_{2} \mathrm{S}_{3} \) showcase variations of yellow due to their distinct electronic structures:

• \( \mathrm{PbCrO}_{4} \) and \( \mathrm{BaCrO}_{4} \) give a vibrant yellow because of their chromate contents.
• \( \mathrm{As}_{2} \mathrm{S}_{3} \), also yellow, is recognized as orpiment, an ancient pigment.
• \( \mathrm{PbI}_{2} \), while still yellow, has a paler shade than the chromates.

These colors are not merely aesthetic; they provide clues in chemical identification and help distinguish between similar compounds.