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

Question

Which of the following is a synthetic dye? (a) phenolphthalein (b) alizarin (c) martius yellow (d) malachite green

Step-by-Step Solution

Answer

Malachite green is a synthetic dye.

Step 1: Understand the Question

To solve this question, we need to identify which of the given options is a synthetic dye. Synthetic dyes are artificially created in laboratories, as opposed to natural dyes, which come from natural sources like plants, animals, or minerals.

Step 2: Examine the Options

We have four options: phenolphthalein, alizarin, martius yellow, and malachite green. We need to categorize each as either synthetic or natural dyes.

Step 3: Classify Each Option

Phenolphthalein is known as a synthetic dye commonly used as a pH indicator in laboratories. Alizarin was originally derived naturally but also has synthetic forms. Martius yellow is a synthetic dye used in biology. Malachite green is a synthetic dye used in industries such as textiles and aquaculture.

Step 4: Identify the Common Synthetic Dye

While all the options, except alizarin in its natural form, can be synthetic, malachite green is widely recognized as a synthetic dye commonly used for industrial purposes.

Key Concepts

Phenolphthalein

Phenolphthalein is a fascinating chemical compound that primarily serves as an indicator in acid-base titrations. While it helps in visualizing pH changes, it is crucial to understand its relation to synthetic dyes.

Phenolphthalein belongs to a class of dyes created through synthetic processes. Laboratory chemists craft phenolphthalein through intricate chemical reactions. In its synthesized form, it is a white, crystalline powder that becomes famous when dissolved. Upon interaction with different pH levels, it transcends from being colorless in acidic solutions to turning a vibrant pink in basic solutions.

• Color change: This transition occurs around a pH range of 8.2 to 10.0.
• Utility: Widely used in titrations for its clear endpoint indication.

Understanding phenolphthalein helps illuminate the creative ways scientists have enhanced older practices through modern technological processes.

Alizarin

Originally extracted from the madder plant, alizarin initially represented natural dye. However, it serves a dual identity due to its synthetic version developed in the 19th century. This transition marks a significant change in chemical industries.

Once chemists figured out how to create alizarin synthetically, it became easier and less costly to produce this rich, deep red hue. It is primarily used in textile industries to dye cotton and wool.

• Synthesis Method: Using anthraquinone, a process effectively copies plant-derived compounds.
• Benefits: Synthesized alizarin offers consistent quality and color.

In doing so, synthetic alizarin expanded possibilities within the textile industry, pushing boundaries of color application.

Martius Yellow

Martius yellow is an intriguing example of synthetic dye discovery tailored for specific uses. Initially synthesized by German chemist Carl Alexander von Martius in the second half of the 19th century, this dye quickly found niche applications.

Particularly within biological studies, Martius yellow functions as a stain, offering detailed examinations of cellular structures. Through its bright yellow color, it highlights various biological tissues clearly.

• Functions: Useful in differentiating cellular components under a microscope.
• History: Its creation represented early modern chemistry's ability to craft purpose-specific dyes.

Martius yellow exemplifies how synthetic dyes advance scientific research by enabling detailed observation and study.

Malachite Green

Malachite green is a prominent synthetic dye, celebrated for its vibrant green hue and wide range of applications. Unlike the naturally occurring mineral malachite, malachite green is manufactured through chemical synthesis.

Known for its effectiveness as a colorant in textiles, malachite green extends its usefulness into aquaculture and bacteriological settings.

• Applications: Often utilized in ornamental fish farming to combat fungal and parasitic infections.
• Characteristics: Although vibrant and intense, concerns have been raised regarding its safety for both humans and wildlife.

The synthetic origin of malachite green not only underscores innovation in chemistry but also cautions on sustainable use and potential ecological impacts.