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

The synthetic dyes are martius yellow and malachite green.

Step 1: Understand the Question

The question asks for the identification of a synthetic dye among the given options. Synthetic dyes are man-made dyes produced through chemical processes, as opposed to natural dyes which are derived from natural sources like plants or animals.

Step 2: Analyze Each Option

Review each option to understand its origin and classification: **(a) phenolphthalein** - This is an organic compound used as an indicator in titrations. It is synthetic. **(b) alizarin** - Originally derived from madder plants, now commonly synthesized, this dye is known for its use in producing red colors. **(c) martius yellow** - A synthetic dye commonly used in dyeing silk. **(d) malachite green** - This is a synthetic dye used to dye materials like silk, leather, and paper.

Step 3: Identify the Synthetic Dye

From the analysis in Step 2, identify which options are synthetic dyes. - Phenolphthalein, martius yellow, and malachite green are all synthetic. - Alizarin, although historically natural, is now often synthetic. Especially considering the context, the queried synthetic dyes are martius yellow (c) and malachite green (d).

Key Concepts

Phenolphthalein

Phenolphthalein is a fascinating compound with versatile uses. Known primarily for its role as an acid-base indicator in chemistry, it changes color depending on the pH level of a solution. When added to a basic solution, it turns pink, and in acidic ones, it is colorless. This makes phenolphthalein an indispensable tool in titrations.
While primarily an indicator, it is indeed a synthetic dye due to its artificial synthesis through chemical reactions. The synthesis involves the condensation of phthalic anhydride with phenols in the presence of an acid catalyst.

• Role in Chemistry: Often used in laboratory experiments to determine the acidity or alkalinity of a solution.
• Synthesis Process: Produced through a reaction involving phthalic anhydride and phenols.

Understanding phenolphthalein’s synthetic nature highlights the innovation in chemical manufacturing that allows for its production, diverging from reliance on nature-derived substances.

Alizarin

Alizarin is an interesting compound with a rich history in the world of dyes. Traditionally, alizarin came from the roots of the madder plant, used for centuries to produce bright red colors. Today, it is typically synthesized, showcasing how advancements in chemistry have transformed natural processes into synthetic ones.
Modern synthesis of alizarin involves a series of reactions beginning with anthraquinone intermediates. These synthetic routes not only replicate the vibrant color but also enhance purity and consistency, offering advantages over the traditional method.

• Historical Use: Derived from madder roots, highly prized for red hues.
• Synthetic Production: Provides enhanced consistency and purity, demonstrating chemistry's impact on dye manufacturing.

Switching to synthetic production of alizarin was driven by the need for more reliable and available sources of the dye, improving its application in textiles and art.

Martius Yellow

Martius Yellow stands out in the world of dyes for its distinctive bright yellow coloring. This is a synthetic dye, meaning it was created through chemical processes rather than being found naturally.
The synthesis of Martius Yellow typically involves the reaction of nitrophenol with diazonium compounds. Its vivid yellow color makes it popular for dyeing silk and other textiles, ensuring a bright and eye-catching appearance.

• Chemical Synthesis: Created through a reaction involving nitrophenol.
• Applications: Widely used in silk dyeing, impressive for its bright yellow hue.

This synthetic origin illustrates just one of many ways chemistry contributes to industrial applications, making vibrant colors easily achievable for textiles.

Malachite Green

Malachite Green is a prominent dye with an interesting history and varied applications. As a synthetic dye, it is produced chemically rather than extracted from a natural source.
Malachite Green is synthesized through a process involving benzaldehyde and dimethylaniline, leading to its characteristic vivid green color. This dye is commonly used to color materials such as silk, leather, and paper.

• Synthesis Process: Involves benzaldehyde and dimethylaniline, generating its distinctive green hue.
• Usage: Popular for dyeing and also used in aquaculture and microbiology.

Despite concerns over its safety and environmental impact, malachite green continues to be relevant in various sectors, showcasing the balance between chemical utility and regulation.