Problem 127 - A Complete Resource Book in Chemistry for JEE Main

Question

In the reaction \(\mathrm{A}+2 \mathrm{~B}+\mathrm{H}_{2} \mathrm{O} \longrightarrow \mathrm{C}+2 \mathrm{D}\) if \(\mathrm{A}\) is \(\mathrm{HNO}_{2}\) and \(\mathrm{C}\) is \(\mathrm{NH}_{2} \mathrm{OH}\) then \(\mathrm{B}\) and \(\mathrm{D}\) are respectively (a) \(\mathrm{H}_{2} \mathrm{SO}_{4}\) and \(\mathrm{SO}_{3}\) (b) \(\mathrm{H}_{2} \mathrm{SO}_{4}\) and \(\mathrm{H}_{2} \mathrm{SO}_{3}\) (c) \(\mathrm{H}_{2} \mathrm{SO}_{3}\) and \(\mathrm{H}_{2} \mathrm{SO}_{4}\) (d) \(\mathrm{H}_{2} \mathrm{SO}_{3}\) and \(\mathrm{SO}_{2}\)

Step-by-Step Solution

Answer

Option (d): \( \mathrm{B} = \mathrm{H}_{2} \mathrm{SO}_{3} \) and \( \mathrm{D} = \mathrm{SO}_{2} \).

Step 1: Identify Given Molecules

We are given that \( \mathrm{A} \) is \( \mathrm{HNO}_{2} \) and \( \mathrm{C} \) is \( \mathrm{NH}_{2} \mathrm{OH} \). We need to determine what \( \mathrm{B} \) and \( \mathrm{D} \) represent based on the reaction.

Step 2: Analyze the Reaction

The given chemical reaction is \( \mathrm{A} + 2 \mathrm{B} + \mathrm{H}_{2} \mathrm{O} \rightarrow \mathrm{C} + 2 \mathrm{D} \). Substituting the known compounds, we have:\[ \mathrm{HNO}_{2} + 2 \mathrm{B} + \mathrm{H}_{2} \mathrm{O} \rightarrow \mathrm{NH}_{2} \mathrm{OH} + 2 \mathrm{D} \] Our task is now to infer \( \mathrm{B} \) and \( \mathrm{D} \) based on the context of typical chemical reactions and the options given.

Step 3: Consider the Conservation of Atoms

The chemical reaction must conserve the number of atoms of each element. Notice that \( \mathrm{C} \) (\( \mathrm{NH}_{2} \mathrm{OH} \)) is formed from \( \mathrm{A} \) (\( \mathrm{HNO}_{2} \)), and since \( \mathrm{NH}_{2} \) is involved, \( \mathrm{D} \) likely involves removing oxygen from a leftover element. Since sulfur compounds \( \mathrm{SO}_{2} \) and \( \mathrm{H}_{2} \mathrm{SO}_{4} \) are given as options for \( \mathrm{D} \), we can consider them.

Step 4: Use the Options to Determine \( \mathrm{B} \) and \( \mathrm{D} \)

Examine the options:1. **(a)** \( \mathrm{B} = \mathrm{H}_{2} \mathrm{SO}_{4}, D = \mathrm{SO}_{3} \)2. **(b)** \( \mathrm{B} = \mathrm{H}_{2} \mathrm{SO}_{4}, D = \mathrm{H}_{2} \mathrm{SO}_{3} \)3. **(c)** \( \mathrm{B} = \mathrm{H}_{2} \mathrm{SO}_{3}, D = \mathrm{H}_{2} \mathrm{SO}_{4} \)4. **(d)** \( \mathrm{B} = \mathrm{H}_{2} \mathrm{SO}_{3}, D = \mathrm{SO}_{2} \)Based on possible common reactions, option **(d)** makes chemical sense since\( \mathrm{HNO}_{2} + 2 \mathrm{H}_{2} \mathrm{SO}_{3} + \mathrm{H}_{2} \mathrm{O} \rightarrow \mathrm{NH}_{2} \mathrm{OH} + 2 \mathrm{SO}_{2} \) illustrates decomposition of sulfuric acid to sulfur dioxide, maintaining conservation of atoms.

Key Concepts

Stoichiometry

Learning stoichiometry helps us understand the quantitative relationship between reactants and products in a chemical reaction. In simple terms, it is like a recipe that tells us the exact proportions of each ingredient needed to form the final product. This ensures that the reaction goes smoothly without any leftover reactants or missing desired output.
For instance, in the given reaction of \( \text{HNO}_2 + 2\text{B} + \text{H}_2\text{O} \rightarrow \text{NH}_2\text{OH} + 2\text{D} \), stoichiometry helps calculate how much of substance \( B \) is needed to yield substance \( D \) based on the starting material, \( A \), and the resulting product, \( C \).
Understanding this concept is vital for predicting how a chemical reaction will proceed and the maximum amount of product that can be formed from a given amount of reactants.

Conservation of Mass in Reactions

The principle of conservation of mass states that mass is neither created nor destroyed in a chemical reaction. This means the mass of the reactants must equal the mass of the products. It is like weighing all the ingredients before and after a cooking recipe to ensure you account for everything.
In the given chemical reaction of \( \text{HNO}_2 + 2\text{H}_2\text{SO}_3 + \text{H}_2\text{O} \rightarrow \text{NH}_2\text{OH} + 2\text{SO}_2 \), the number of each type of atom on the reactant side must equal the number of each type on the product side. This principle helps us figure out the unknowns in a reaction by checking for balance in terms of atoms and, consequently, mass.
Ensuring the conservation of mass is crucial in verifying the feasibility and balance of chemical reactions, such as determining that \( \text{H}_2\text{SO}_3 \) and \( \text{SO}_2 \) are the correct candidates for \( \text{B} \) and \( \text{D} \) respectively.

Chemical Formula Interpretation

Interpreting a chemical formula involves understanding the elements involved, their quantities, and the type of chemical bonds they share. Each formula gives a miniature snapshot of the compound's structure. For example, \( \text{HNO}_2 \) signifies a molecule with one hydrogen atom, one nitrogen atom, and two oxygen atoms.
In the reaction context, interpreting \( \text{NH}_2\text{OH} \), the product \( \text{C} \), shows us that the compound consists of one nitrogen, two hydrogen from the \( \text{NH}_2 \) group, and one hydroxyl group \( \text{OH} \).
This clear reading aids in balancing chemical equations by ensuring you have a solid grasp of individual components. Chemical formulas serve as essential tools to understand and predict the outcomes in reactions by revealing the elemental building blocks and molecular configurations involved.