Question

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

Short answer

(d) Malachite green

Step-by-step solution

Understand the Question

The question asks us to identify which among the given options is a synthetic dye. A synthetic dye is a type of dye made through chemical synthesis, typically from petrochemical sources.

Option Analysis - Phenolphthalein

Phenolphthalein is best known as a chemical compound used as an acid-base indicator in laboratory settings. It changes color depending on the pH level of the solution it is in.

Option Analysis - Alizarin

Alizarin is a dye originally derived from the madder plant, but now usually produced synthetically. It is a red dye used in textiles and art.

Option Analysis - Martius Yellow

Martius yellow is a synthetic dye used primarily in histology for staining cell tissues in microscopic examinations.

Option Analysis - Malachite Green

Malachite green is a synthetic dye used in aquaculture and as a biological stain, known for its vibrant green color.

Conclusion

Among the options, phenolphthalein and alizarin have specific historical contexts related to natural derivation and alternative uses. Martius yellow and malachite green are noted for their uses primarily tied to their synthetic creation. Of these, malachite green is most commonly associated only with being a synthetic dye without alternative significant natural history.

Key concepts

Phenolphthalein

Phenolphthalein is a well-known chemical compound, often used as an acid-base indicator in laboratory settings. Its importance in chemistry education can't be overstated. This compound exhibits a fascinating property where it changes color based on the pH level of a solution. In neutral or mildly acidic solutions, phenolphthalein appears colorless. However, as the pH level rises past about 8.2, it turns a vibrant magenta, eventually fading to a clear solution above pH 12. This striking color transition makes it invaluable for titrations, helping chemists determine the endpoint of an acid-base reaction. Phenolphthalein is technically considered a synthetic dye due to its chemical composition and laboratory preparation, but it is more commonly recognized for its use as an indicator rather than a traditional dye used in textiles or art. Its synthesis involves phthalic anhydride and phenol, providing a classic example of early synthetic dye chemistry.

Alizarin

Alizarin boasts a rich history in the world of dyes, once extracted from the madder plant roots for its beautiful red color. Traditionally used in textile dyeing, it was highly prized in ancient fabrics. However, the advent of synthetic chemistry allowed for the replication of Alizarin’s molecular structure, leading to its widespread synthetic production. This synthetic version of Alizarin retains all the desirable properties of its natural counterpart, such as colorfastness and vibrancy. Its synthetic nature makes it more economical and available without the need for extensive plant resources. Alizarin is noteworthy for its use in art and textiles, and also plays a role in chemical staining processes.

Martius Yellow

Martius Yellow is a synthetic dye notable for its use in the field of histology. It is named after the German chemist Carl Alexander von Martius, who contributed to its development. Specifically designed to identify and differentiate biological tissues, it stains cell components for microscopic examination. This vivid yellow dye aids scientists and researchers in visualizing structures in biological specimens, enabling detailed studies in biochemistry and pathology. While Martius Yellow might not be as commonly recognized outside its scientific applications, its role in research highlights the significance of synthetic dyes in modern science. These dyes are crucial for clarifying complex biological patterns that are otherwise challenging to distinguish.

Malachite Green

Malachite Green is a vibrant green synthetic dye known for its broad range of applications. Originally developed for use in the textile industry, it has since found numerous other uses owing to its strong coloring properties. One of the noteworthy applications of Malachite Green is in aquaculture, where it is used to treat fungal infections in fish. Its efficacy in killing certain fungi and parasites makes it a staple in fish health management. Beyond this, it serves as a biological stain in laboratories, helping to highlight specific cellular components under a microscope. However, despite its benefits, it is important to handle Malachite Green with care due to potential toxicity concerns, reminding us of the balance between utility and safety in synthetic chemistry.