Problem 11 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

For the identification of \(\beta\)-naphthol using dye test, it is necessary to use [Adv. 2014] (a) Dichloromethane solution of \(\beta\)-naphthol (b) Acidic solution of \(\beta\)-naphthol (c) Neutral solution of \(\beta\)-naphthol (d) Alkaline solution of \(\beta\)-naphthol

Step-by-Step Solution

Answer

(d) Alkaline solution of \(\beta\)-naphthol.

Step 1: Understanding the Problem

To identify \(\beta\)-naphthol using a dye test, you need to determine what kind of solution will react correctly with the dye to confirm its presence. The options include acidic, neutral, or alkaline environments, as well as a dichloromethane solution.

Step 2: Reviewing Chemical Properties of \(\beta\)-naphthol

\(\beta\)-naphthol is known to react differently in various pH environments. In acidic and neutral solutions, it remains mostly non-ionic, while in an alkaline solution, it forms an anion that can further react with dyes, typically used for detection.

Step 3: Assessing Reaction with Dye

In a dye test, \(\beta\)-naphthol is often used in an alkaline medium, as the alkaline environment deprotonates hydroxyl group, making \(\beta\)-naphthol an anion which can effectively bind with dye molecules, confirming its presence through a visible color change.

Step 4: Selecting the Correct Solution Type

Based on the chemical properties and typical reactions in a dye test, an alkaline solution of \(\beta\)-naphthol is needed to facilitate the desired reaction with the dye, making option (d) the correct choice.

Key Concepts

Beta-naphthol

Beta-naphthol is an organic compound that belongs to the naphthalene family. It is a crystalline solid with a distinct odor. The molecule is composed of two benzene rings fused together, with a hydroxyl group (-OH) attached to one of the carbons in the ring. This hydroxyl group is what differentiates beta-naphthol from other chemicals in its family, contributing to its unique properties.

One key property of beta-naphthol is its ability to react in different pH environments. In acidic or neutral solutions, beta-naphthol tends to remain mostly non-ionic, meaning it does not easily form ions. However, in an alkaline solution, beta-naphthol behaves differently. The hydroxyl group can lose a hydrogen ion (H⁺) to form an anion. This chemical behavior is crucial when using beta-naphthol in various applications, such as dye tests where its ionic form is required for reactions.

Dye Test

A dye test is a chemical procedure used to identify specific compounds. In the context of beta-naphthol, the dye test involves reacting it with a dye to observe a color change. This change signifies the presence of beta-naphthol in a solution.

For the dye test to work effectively with beta-naphthol, it is generally performed in an alkaline environment. This is because the hydroxyl group in beta-naphthol needs to be deprotonated to form an anion. This anionic form of beta-naphthol can then bind effectively with dye molecules, allowing a visible color change that confirms the presence of beta-naphthol.

Some key points about dye tests include:

• The choice of environment (acidic, neutral, or alkaline) can greatly influence the reaction.
• In an alkaline solution, beta-naphthol reacts more actively, enhancing the binding with dyes.
• Dye tests are visual and rely on the distinctive color change for clear identification of the substance.

Alkaline Solution

An alkaline solution refers to a basic solution, characterized by its pH above 7. In chemistry, alkaline solutions are known to neutralize acids and are often used when deprotonation of a molecule like beta-naphthol is required.

When beta-naphthol is placed in an alkaline solution, it loses a hydrogen ion from its hydroxyl group. This process creates an anion form of beta-naphthol, which is more reactive. This increased reactivity is what makes alkaline solutions essential for certain chemical tests, including the dye test.

Here are some notable aspects of alkaline solutions:

• They facilitate reactions by altering the charge and reactivity of molecules.
• Common examples include solutions of sodium hydroxide (NaOH) or potassium hydroxide (KOH).
• In dye tests, they help certain molecules, like beta-naphthol, form an ionic state needed for interaction with dyes.

By manipulating the pH of a solution, scientists can control how substances like beta-naphthol behave, enabling precise identification in laboratory settings.