Problem 146 - A Complete Resource Book in Chemistry for JEE Main

Question

Match the following $$ \begin{array}{ll} \hline \text { Column-I } & \text { Column-II } \\ \hline \text { (a) Glucose } & \text { (p) Tollen's reagent } \\ \text { (b) Acetaldehyde } & \text { (q) Bromine water } \\ \text { (c) Sucrose } & \text { (r) Phenyl hydrazine } \\ \text { (d) Maltose } & \text { (s) Disaccharide } \\ & \text { (t) Ammonia } \end{array} $$

Step-by-Step Solution

Answer

(a) - (p), (b) - (r), (c) - (s), (d) - (q).

Step 1: Analyze Glucose Reactions

Glucose is a simple sugar and a reducing agent. It can be oxidized by Tollen's reagent, which is used to detect the presence of aldehyde groups or reducing sugars. Therefore, glucose corresponds to option (p) Tollen's reagent.

Step 2: Analyze Acetaldehyde Reactions

Acetaldehyde is an aldehyde that reacts well with various reagents. It forms a crystalline solid when it reacts with phenylhydrazine. Therefore, acetaldehyde corresponds to option (r) Phenyl hydrazine.

Step 3: Analyze Sucrose Characteristics

Sucrose is a common disaccharide composed of glucose and fructose units. It is not a reducing sugar. It fits well with option (s) Disaccharide.

Step 4: Analyze Maltose Characteristics

Maltose is a reducing disaccharide, composed of two glucose molecules linked together. Bromine water can be used to identify reducing properties in disaccharides. Therefore, maltose corresponds to option (q) Bromine water.

Key Concepts

Reducing Sugars

Reducing sugars are carbohydrates that can act as reducing agents. This is because they possess free aldehyde or ketone groups capable of reducing mild oxidizing agents.

Examples of reducing sugars include:

• Glucose
• Maltose
• Fructose

Reducing sugars can be detected using certain chemical reagents. Tollen’s reagent is a popular choice for identifying these sugars due to its silver mirror test. This test reveals the presence of aldehyde groups by forming a silver precipitate.

Understanding the concept of reducing sugars is essential in organic chemistry, especially when studying reactions and behaviors of different carbohydrates.

Tollen's Reagent

Tollen’s reagent is a chemical solution used to detect the presence of aldehydes and reducing sugars. It consists of an ammoniacal silver nitrate solution. When added to a solution containing aldehydes or reducing sugars, the reagent forms a distinctive silver mirror on the inner surface of the reaction vessel.

This occurs because:

• The aldehyde group reduces the silver ion to metallic silver.
• It is a gentle oxidizing agent, ensuring that only specific functional groups react.

Tollen’s reagent is thus an excellent tool in laboratory settings for confirming the presence of these functional groups. As sugars like glucose react with Tollen’s reagent, they are classified among reducing sugars.

Disaccharides

Disaccharides are carbohydrates composed of two monosaccharide units. They form through a glycosidic bond between the monosaccharides, and are a common type of sugar found in many foods.

Examples of disaccharides include:

• Sucrose (composed of glucose and fructose)
• Maltose (composed of two glucose units)
• Lactose (composed of glucose and galactose)

Not all disaccharides are reducing sugars. For instance, sucrose is a non-reducing sugar because its glycosidic bond involves an anomeric carbon that lacks a free reducing end. This distinction is significant when characterizing sugar types and studying their chemical behaviors.

Aldehyde Reactions

Aldehyde reactions hold a central place in organic chemistry due to the versatile nature of the aldehyde group (\(\text{-CHO}\)). The presence of this functional group allows aldehydes to undergo various reactions, which are useful in synthesis and analysis.

Key reactions include:

• Oxidation (Aldehydes oxidize to form carboxylic acids.)
• Formation of hydrazones with phenylhydrazine
• Reduction (They can be reduced to form alcohols.)

For example, acetaldehyde reacts with phenylhydrazine to form a hydrazone, which is a stable and identifiable compound. Understanding how aldehydes react is vital for predicting their behavior in different chemical environments.