Question

In the given reaction, value of \(n\) is Glucose \(+\) n Phenylhydrazine \(\longrightarrow\) Osazone (A) Three (B) Two (C) One (D) Four

Short answer

The value of \(n\) in the given reaction is 2. Therefore, the correct answer is (B) Two.

Step-by-step solution

Write down the given chemical reaction

Glucose + n Phenylhydrazine → Osazone

Identify the molecular formulas of the species involved in the reaction

\( Glucose: (C_6H_{12}O_6) \) \( Phenylhydrazine: (C_6H_5NHNH_2) \) \( Osazone: (C_6H_8N_4O_4) \)

Balance the equation to find the value of n

To balance the equation, we need to make sure that there are an equal number of each element in both the reactant side and the product side of the equation. \( (C_6H_{12}O_6) + n(C_6H_5NHNH_2) \rightarrow (C_6H_8N_4O_4) \) Balancing the number of Nitrogen atoms: \( 2n = 4\) (because there are two Nitrogen atoms in the Phenylhydrazine molecule and four Nitrogen atoms in the Osazone molecule) To find the value of n, divide both sides by 2: \( n = \frac{4}{2} \) The resulting value for n is: \( n = 2 \) So the balanced equation becomes: \( (C_6H_{12}O_6) + 2(C_6H_5NHNH_2) \rightarrow (C_6H_8N_4O_4) \) Since we have found the value of \(n\) to be 2, the correct answer is (B) Two.

Key concepts

Osazone Formation

Osazone formation is a fascinating process that involves the reaction of reducing sugars, like glucose, with phenylhydrazine to form a compound known as an osazone. This reaction is particularly important in the field of carbohydrate chemistry as it can be used to characterize and identify different sugars.

To form an osazone, the reducing sugar initially undergoes a process called enolization, where it transforms into an enol form. Phenylhydrazine then reacts with the enol to create a hydrazone, and a subsequent reaction with another molecule of phenylhydrazine leads to the formation of the final osazone product, which tends to crystallize and can be seen under a microscope.

The structure of an osazone includes a distinctive arrangement of nitrogen atoms, typically with two nitrogen atoms adjacent to each other. This structure is a result of the nitrogen atoms from phenylhydrazine attaching to the carbon atoms of the sugar molecule that were originally part of a carbonyl group (a carbon double-bonded to an oxygen).

Stoichiometry

Stoichiometry is the branch of chemistry that deals with the quantitative relationships between reactants and products in a chemical reaction. It is a key concept in understanding how to balance chemical equations, which involves ensuring that the number of atoms of each element is conserved from the reactants to the products.

The stoichiometric coefficients, represented by the variable 'n' in our exercise, are the numbers that appear in front of the chemical species in a balanced chemical equation. These numbers are crucial because they indicate the proportions in which reactants combine to produce the products. As shown in the exercise, determining the correct value for 'n' ensures that the chemical equation adheres to the law of conservation of mass.

Moreover, stoichiometry goes beyond just balancing equations. It enables chemists to predict the amounts of products that can be formed from a given amount of reactants and to calculate the amount of reactants needed to produce a desired quantity of product. These calculations are fundamental for various applications, from laboratory syntheses to industrial production processes.

Phenylhydrazine Reaction

The phenylhydrazine reaction forms the basis of osazone formation, as mentioned earlier. Phenylhydrazine, with the chemical formula \(C_6H_5NHNH_2\), is an organic compound commonly used to identify reducing sugars through this specific reaction.

When phenylhydrazine is introduced to a solution containing a reducing sugar, it reacts with the aldehyde or ketone group of the sugar. The initial product of this reaction is a hydrazone, which then undergoes further reaction in the presence of excess phenylhydrazine to form the osazone. Phenylhydrazine specifically targets the carbonyl groups present in the sugar, which is what makes it a powerful tool for distinguishing between different sugars based on their osazone formation behavior.

The reaction with phenylhydrazine not only serves as a qualitative test for the presence of reducing sugars but can also be used to deduce the structure of the sugar based on the properties of the formed osazone. The specificity of this reaction and the crystalline nature of osazones make it a valuable method in organic chemistry and biochemical studies.