Question

This section contains multiple choice questions. Each question has 4 choices (a), (b), (c) and (d), out of which ONLY ONE is correct. One mole of glucose can react with how many moles of phenyl hydrazine to form osazone? (a) 1 (b) 2 (c) 3 (d) 4

Short answer

Answer: 3 moles

Step-by-step solution

Write the reaction of glucose with phenyl hydrazine

Glucose reacts with phenyl hydrazine to form an intermediate Schiff base, which then reacts with two more moles of phenyl hydrazine to form the final osazone product. The overall reaction can be expressed as: Glucose + 3 Phenyl hydrazine → Osazone + 3 molecules of Water

Determine the stoichiometry of the reaction

In the reaction, we can see that one mole of glucose reacts with three moles of phenyl hydrazine to form one mole of osazone. So the stoichiometry of the reaction is: 1 Glucose : 3 Phenyl hydrazine

Identify the correct option

Based on the stoichiometry of the reaction, one mole of glucose reacts with three moles of phenyl hydrazine. Therefore, the correct option is: (c) 3

Key concepts

Phenyl Hydrazine Reaction

Phenyl hydrazine is a reagent that is commonly used in organic chemistry to identify reducing sugars, such as glucose, through a process known as osazone formation. This reaction involves the conversion of the sugar into a bright yellow crystalline compound called an osazone. When glucose is treated with phenyl hydrazine, it initially undergoes a condensation reaction to form a Schiff base, also known as an imine.

The initial step involves the carbonyl group of the glucose reacting with the phenyl hydrazine, facilitating the loss of water and creating the Schiff base. Subsequently, the Schiff base further reacts with two more molecules of phenyl hydrazine, leading to the formation of the osazone. This process not only exemplifies the versatile nature of phenyl hydrazine reactions but also highlights how multiple moles of the reagent can add to a single mole of substrate, in this case, glucose, in a sequential fashion.

Stoichiometry

Stoichiometry is a foundational concept in chemistry that involves the quantitative relationships between the amounts of reactants and products in a chemical reaction. In the example of glucose reacting with phenyl hydrazine, stoichiometry dictates how many moles of each reactant are needed to form the product.

In this reaction, the stoichiometry is 1 mole of glucose to 3 moles of phenyl hydrazine. This numerical relationship is crucial for predicting the yield of osazone formed during the reaction. For students, understanding stoichiometry is not just about memorizing ratios; it's about comprehending the balance and conservation of mass in chemical processes. It guides us to precisely measure the amounts required for a reaction to proceed to completion and informs us about the proportionality of reactants consumed and products formed.

Schiff Base

Schiff bases are compounds that represent an important class of organic intermediates in various chemical reactions, including osazone formation. They are formed by the condensation of a primary amine, such as phenyl hydrazine, with a carbonyl compound, such as an aldehyde or ketone.

In the context of the glucose reaction, the Schiff base is the intermediate compound that arises after the initial attachment of one mole of phenyl hydrazine to the glucose molecule. The creation of a Schiff base is often characterized by the elimination of water and can be identified by its structure, which includes a carbon-nitrogen double bond. The Schiff base serves as the key intermediate that facilitates further reaction with additional phenyl hydrazine molecules to eventually form the osazone.

Understanding the role of Schiff bases helps explain reaction mechanisms and the structural transformations that occur during the synthesis of various compounds, including osazones from reducing sugars.