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: Examine each statement

Let's carefully evaluate each statement to determine if it is correct. (1) Glacial acetic acid is used as a solvent in the preparation of p-nitroacetanilide. This is correct; glacial acetic acid is a common solvent for acetylation reactions, such as the preparation of p-nitroacetanilide. (2) Potash alum is used as a mordant in dyeing. Correct, as potash alum is traditionally used as a mordant in fabric dyeing to help fix dyes. (3) Potassium alum is used to remove positively charged impurities from water. This statement is incorrect; potassium alum is commonly used to remove negatively charged impurities from water by causing them to coagulate. (4) Iodoform has antiseptic properties also. This is correct; iodoform has mild antiseptic properties.

Step 2: Identify the correct options

From Step 1, we found that statements 1, 2, and 4 are correct. Statement 3 is incorrect. Now, we'll match the correct statements with the given options: - (a) 2 and 4: Correct, as both statement 2 and 4 are true. - (b) 1, 3, and 4: Incorrect, as statement 3 is false. - (c) 1 and 3: Incorrect, as statement 3 is false. - (d) 1, 2, and 4: Correct, as statements 1, 2, and 4 are true.

Key Concepts

Glacial Acetic Acid

Glacial acetic acid is an extremely important compound in chemistry. It is the undiluted form of acetic acid and is used as a solvent for many chemical reactions. Imagine vinegar, just much more concentrated! It's called "glacial" because it can form ice-like crystals around room temperature.

One of its popular uses is in the acetylation process, which involves introducing an acetyl group into another compound. This is important in producing substances like p-nitroacetanilide. In such reactions, glacial acetic acid often acts as a solvent because it can dissolve both organic and inorganic compounds effectively.

• Solvent for acetylation: Helps in creating different chemicals.
• Strong concentration: Much stronger than household vinegar.
• Ice-like appearance: Forms crystals easily.

Remember, though potent and useful, it should be handled with care due to its corrosive nature.

Potash Alum

Potash alum, or potassium aluminum sulfate, is renowned for its use in fabric dyeing. It acts as a mordant, a substance that helps fix dyes onto fibers, ensuring that the hues remain vibrant and don't wash away easily.

This white crystalline powder works by forming a bond with both the dye and fiber, creating a stable link that withstands washing and exposure to sunlight.

• Mordant in dyeing: Fixes colors onto fabrics.
• Chemical bonding: Ensures long-lasting fabric coloring.

Beyond textiles, potash alum finds use in water purification and as an astringent in medicinal practices. However, its principal role in the context here is anchoring dyes.

Iodoform

Iodoform is a yellow, crystalline compound with the chemical formula CHI₃. Historically, it has been used for its antiseptic properties. If you remember early bandages and wound dressings, iodoform was a common ingredient due to its ability to kill bacteria and prevent infections.

Though not as common in modern medicine, where more advanced antiseptics have taken over, it's still a part of the curious history of chemical usage in healthcare.

• Antiseptic properties: Deter bacterial growth.
• Distinct smell: Familiar medicinal scent.

Iodoform's smell is quite pungent, often described as slightly sweet and medicinal. Its use in medicine serves as a reminder of how chemistry has continually sought solutions for health challenges.

Chemical Reactions

Chemical reactions are processes where substances, called reactants, transform into different substances, known as products. These transformations are the heart of chemistry and can happen under various conditions.

In our context, we have seen several reactions:
1. Acetylation involves adding an acetyl group to a compound, using solvents like glacial acetic acid.
2. The interaction of potash alum with dyes showcases reactions that bind molecules together.
3. The antimicrobial action of iodoform is another fascinating set of chemical processes.

The nature of these reactions can vary widely. They may require specific conditions, like temperature or catalysts, or be spontaneous.

• Reactants and products: Starting and ending substances.
• Transformation: Essence of chemistry.
• Varied conditions: Not all reactions are the same.

Understanding these changes helps chemists create new substances and solve practical problems.