Problem 5 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

Chlorine on reaction with hot and concentrated sodium hydroxide gives: [Main Jan. 12, 2019 (II)] (a) \(\mathrm{Cl}\) and \(\mathrm{ClO}_{3}^{-}\) (b) \(\mathrm{Cl}^{-}\)and \(\mathrm{ClO}^{-}\) (c) \(\mathrm{ClO}_{3}^{-}\)and \(\mathrm{ClO}_{2}^{-}\) (d) \(\mathrm{Cl}^{-}\)and \(\mathrm{ClO}_{2}^{-}\)

Step-by-Step Solution

Answer

Chlorine reacts with hot, concentrated NaOH to form \(\mathrm{Cl}^-\) and \(\mathrm{ClO}_3^-\).

Step 1: Understand the Reaction

When chlorine ( \(\mathrm{Cl}_2,\) ) reacts with hot and concentrated sodium hydroxide ( \(\mathrm{NaOH},\) ) it undergoes a disproportionation reaction. In these types of reactions, the same element is simultaneously oxidized and reduced to form different products.

Step 2: Set Up the Reaction Equation

Write the chemical equation for the reaction when chlorine reacts with hot and concentrated sodium hydroxide: \[3\mathrm{Cl}_2 + 6\mathrm{NaOH} \rightarrow 5\mathrm{NaCl} + \mathrm{NaClO}_3 + 3\mathrm{H}_2\mathrm{O}\]

Step 3: Identify Oxidation and Reduction Products

In the reaction equation, chlorine ( \(\mathrm{Cl}_2\) ) is reduced to form chloride ions ( \(\mathrm{Cl}^-\) , part of \(\mathrm{NaCl}\) ) and oxidized to form chlorate ions ( \(\mathrm{ClO}_3^-\) , part of \(\mathrm{NaClO}_3\) ). Thus, the products of the reaction are \(\mathrm{Cl}^-\) and \(\mathrm{ClO}_3^-\).

Key Concepts

Chlorine Chemistry

Chlorine chemistry is fascinating due to its wide range of reactions and compounds. Chlorine is a halogen and is found in Group 17 of the periodic table. It's known for its electron-gaining behavior, preferring to achieve a stable configuration by accepting an electron to form chloride ions ( \( ext{Cl}^- \) ).

In the reaction with sodium hydroxide, chlorine exhibits unique properties. It can exist in multiple oxidation states, which allows it to participate in disproportionation reactions, where the same element is both oxidized and reduced. This makes chlorine an essential player in various industrial applications, such as in the manufacturing of disinfectants and PVC plastics.

Chlorine's reactivity is characteristic of its ability to form multiple types of bonds and ions. This is why chlorine is a key component in many chemical reactions and processes in both natural and industrial settings. Understanding its chemistry helps in grasping the broader context of halogens and their practical uses.

Oxidation-Reduction Reactions

Oxidation-reduction reactions, often called redox reactions, are crucial in chemistry as they involve the transfer of electrons between substances.

In these reactions, oxidation refers to the loss of electrons, while reduction is the gain of electrons. When chlorine reacts with hot and concentrated sodium hydroxide, it undergoes both oxidation and reduction. This process is known specifically as a disproportionation reaction.

In the given reaction, chlorine ( \( ext{Cl}_2 \) ) is reduced to chloride ( \( ext{Cl}^- \) ) and oxidized to chlorate ( \( ext{ClO}_3^- \) ).

• Reduction: Chlorine gains electrons to form chloride ions.
• Oxidation: Chlorine loses electrons to form chlorate ions.

This balance of electron transfer is vital for energy production in various chemical processes and reactions. Redox reactions are found everywhere, from biological systems to industrial chemical manufacturing. Developing a robust understanding of these reactions aids in the study of energy flow and transformation.

Chemical Equations

Chemical equations are a symbolic representation of chemical reactions. They display the reactants, products, and the direction of the reaction, providing a concise summary of a given chemical process.

In the context of the exercise, the chemical equation \[ \text{3Cl}_2 + 6\text{NaOH} \rightarrow 5\text{NaCl} + \text{NaClO}_3 + 3\text{H}_2\text{O} \] clearly lays out the starting materials and the products formed.

• Reactants: These are on the left side, where chlorine and sodium hydroxide are the inputs of the reaction.
• Products: On the right, we find sodium chloride, sodium chlorate, and water as the outcome.

Additionally, coefficients before compounds indicate the number of molecules involved, ensuring the equation is balanced, meaning the number of atoms for each element remains constant on both sides. Properly balanced chemical equations are essential for predicting the quantities of products formed and for scaling reactions in industrial applications.