Problem 51 - A Complete Resource Book in Chemistry for JEE Main

Question

The reaction, \(3 \mathrm{ClO}^{-}(\mathrm{aq}) \longrightarrow \mathrm{ClO}_{3}^{-}(\mathrm{aq})+2 \mathrm{Cl}^{-}(\mathrm{aq})\) is an example of (a) oxidation reaction (b) reduction reaction (c) disproportionation reaction (d) decomposition reaction

Step-by-Step Solution

Answer

The reaction is a disproportionation reaction (c).

Step 1: Identify the Reaction Type

The reaction involves a single reactant, \(3 \mathrm{ClO}^{-}\), which transforms into two different products: \( \mathrm{ClO}_{3}^{-}\) and \(2 \mathrm{Cl}^{-}\). Disproportionation reactions are unique because a single substance undergoes both oxidation and reduction to form two different products.

Step 2: Check Oxidation States

Determine the oxidation states of chlorine in \( \mathrm{ClO}^{-} \), \( \mathrm{ClO}_{3}^{-} \), and \( \mathrm{Cl}^{-} \). In \( \mathrm{ClO}^{-} \), chlorine has an oxidation state of +1. In \( \mathrm{ClO}_{3}^{-} \), chlorine is +5, and in \( \mathrm{Cl}^{-} \), it is -1. This indicates that chlorine is both oxidized (from +1 to +5) and reduced (from +1 to -1).

Step 3: Analyze the Disproportionation

Since the same species, \( \mathrm{ClO}^{-} \), undergoes simultaneous oxidation (to \( \mathrm{ClO}_{3}^{-} \)) and reduction (to \( \mathrm{Cl}^{-} \)), this is characteristic of a disproportionation reaction.

Key Concepts

Oxidation Reaction

An oxidation reaction occurs when a chemical species loses electrons. This process increases the oxidation state of the element involved. In the given reaction, chlorine is oxidized in one part of the process.

• Originally, in the hypochlorite ion \( \text{ClO}^- \), chlorine has an oxidation state of +1.
• When it is converted into the chlorate ion \( \text{ClO}_3^- \), the oxidation state of chlorine increases to +5.

This increase in oxidation state indicates the loss of electrons, which is characteristic of oxidation. Think of it as chlorine "gaining positivity." The higher the positive charge, the more oxidized a substance is.

Reduction Reaction

Reduction reactions are the opposite of oxidation reactions. They occur when a species gains electrons and thus reduces its oxidation state. In the exercise:

• Chlorine in \( \text{ClO}^- \) has an oxidation state of +1.
• This changes to -1 in \( \text{Cl}^- \), indicating a gain of electrons.

Reduction can be remembered by the phrase "reduce the charge," where gaining negatively charged electrons makes the oxidation state lower or more negative. Chlorine, by gaining electrons, is reduced from \( \text{ClO}^- \) to \( \text{Cl}^- \). This process showcases how electrons can change the chemical character of an element.

Oxidation States

Understanding oxidation states is crucial for identifying oxidation and reduction processes. Oxidation states are imaginary charges assigned to atoms based on certain rules for electron distribution in a molecule.

• In \( \text{ClO}^- \), chlorine's oxidation state is assumed to be +1.
• In \( \text{ClO}_3^- \), the oxidation state shifts to +5.
• In \( \text{Cl}^- \), the state drops to -1.

The purpose of assigning oxidation states is to track the movement of electrons in a chemical reaction. By understanding these changes, one can discern whether electrons are lost or gained, highlighting the processes of oxidation and reduction.

Chemical Reactions in Chemistry

Chemical reactions describe the transformation of substances into new chemical species. They are grouped into different types, such as oxidation and reduction reactions.

• In an oxidation reaction, a chemical species loses electrons.
• Simultaneously, in a reduction reaction, a species gains electrons.
• A combination of these is seen in disproportionation reactions, where a single species undergoes both processes.

The exercise analyzes the reaction of \( 3 \text{ClO}^{-} \to \text{ClO}_{3}^{-} + 2 \text{Cl}^{-} \). This unique disproportionation reaction involves one compound acting as both the oxidized and reduced substance. Understanding these reactions allows insight into the dynamic world of chemistry, where electron exchanges drive the formation of new compounds.