Problem 106 - A Complete Resource Book in Chemistry for JEE Main

Question

Which is correct statement here? (1) Glacial acetic acid is used as a solvent in the preparation of p-nitroacetanilide. (2) Potash alum is used as a mordant in dyeing. (3) Potassium alum is used to remove positively charged impurities from water. (4) Iodoform has antiseptic properties also. (a) 2 and 4 (b) 1,3 and 4 (c) 1 and 3 (d) 1,2 and 4

Step-by-Step Solution

Answer

The correct answer is (d) 1, 2 and 4.

Step 1: Understanding glacial acetic acid usage

Glacial acetic acid is indeed used as a solvent in the preparation of organic compounds such as p-nitroacetanilide. This statement is correct.

Step 2: Potash alum in dyeing

Potash alum, also known simply as alum, is commonly used as a mordant in dyeing processes to fix dyes to fabrics. This statement is correct as well.

Step 3: Potassium alum in water purification

Potassium alum is used to remove negatively charged impurities, not positively charged ones, from water. This process is known as flocculation where the alum helps to clump impurities together for removal. Thus, this statement is incorrect.

Step 4: Iodoform's antiseptic properties

Iodoform is known to have antiseptic properties and has been used in the medical field. This statement is correct.

Step 5: Selecting the correct answer based on verified statements

Identifying which statements are correct: (1) glacial acetic acid as a solvent, (2) potash alum as a mordant, and (4) iodoform's antiseptic properties. Hence, the correct statements are in option (d) 1, 2 and 4.

Key Concepts

Glacial Acetic Acid

Glacial acetic acid is a concentrated form of acetic acid. It is called "glacial" because it forms ice-like crystals at lower temperatures. Acetic acid, with its sharp, vinegar-like smell, is a vital solvent in organic chemistry. It is used in the preparation of numerous chemical compounds.
One such compound is p-nitroacetanilide, where glacial acetic acid acts as an effective solvent. Glacial acetic acid helps dissolve both polar and non-polar substances, making it versatile in chemical reactions. Its ability to participate in acetylation reactions is another reason for its widespread use in synthesis. The solvent property of glacial acetic acid aids in increasing the reaction speed and efficiency.

Potash Alum

Potash alum, also known as potassium alum, is a common ingredient in dyeing processes. Its chemical formula is KAl(SO4)_2·12H2O, which hints at its hydrated crystal structure. Potash alum acts as a mordant, a substance used to fix dyes to fabrics.

• Fixation: Potash alum forms a complex with dye molecules, helping them adhere to the fabric fibers permanently.
• Enhanced Colors: It intensifies the color of the dye, making the hues more vivid and long-lasting.

It's appreciated in the textile industry not only for its effectiveness but also for being relatively safe and non-toxic.

Iodoform

Iodoform is recognized for its antiseptic properties. Chemically known as triiodomethane, it has the formula CHI_3. Historically, iodoform was used extensively in the medical field to disinfect wounds and prevent infection.

• Its distinctive yellow color and smell made it easily recognizable as it was applied to cuts or surgical sites.
• Even today, it serves as an active ingredient in some antiseptic formulations, demonstrating its resilience and timelessness in healthcare.

However, due to the development of more advanced antiseptics, iodoform's usage has slightly diminished, but its efficacy remains indisputable.

Dyeing Processes

Dyeing is an ancient art and science, deeply rooted in textile manufacturing. It involves adding color to textile fibers in a way that the coloring material becomes part of the fiber's structure.
The process of dyeing includes several steps to ensure vibrant and long-lasting colors:

• Preparation: Fabrics are pre-treated to remove impurities, enhancing the adhesion of dyes.
• Dye Application: Depending on the method, dyes can be applied by immersion, spraying, or printing.
• Fixation: Mordants such as potash alum are often used to anchor the dye within the fibers.

Techniques and materials may vary, but the core principles remain the same across different dyeing methods, whether for traditional textiles or modern synthetic fibers.

Water Purification

Water purification methods are essential to providing safe drinking water. One common technique involves the use of alum, particularly in removing impurities through the flocculation process.
Here’s how it works:

• Alum, when added to water, causes suspended particles (often negatively charged) to clump together.
• These larger particles, or flocs, can then be easily removed by sedimentation or filtration, clearing the water of dirt and other impurities.

This method is efficient in large-scale water treatment facilities and helps ensure water safety for communities.