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: Analyze the Reaction Equation

Look at the given reaction: \(3 \mathrm{ClO}^{-}(\mathrm{aq}) \longrightarrow \mathrm{ClO}_{3}^{-}(\mathrm{aq})+2 \mathrm{Cl}^{-}(\mathrm{aq})\). Notice that the same element, chlorine (Cl), appears in different oxidation states in the reactant and product sides. This is a clue that it could be a disproportionation reaction.

Step 2: Identify Oxidation States

Determine the oxidation states of Cl in the reactants and products. In \(\mathrm{ClO}^{-}\), the oxidation state of Cl is +1. In \(\mathrm{ClO}_{3}^{-}\), the oxidation state is +5, and in \(\mathrm{Cl}^{-}\), it is -1.

Step 3: Identify Changes in Oxidation States

Compare the changes: from +1 in \(\mathrm{ClO}^{-}\) to +5 in \(\mathrm{ClO}_{3}^{-}\) (oxidation) and from +1 in \(\mathrm{ClO}^{-}\) to -1 in \(\mathrm{Cl}^{-}\) (reduction). The same species, \(\mathrm{ClO}^{-}\), is both oxidized and reduced.

Step 4: Conclusion Based on Changes

A reaction where a single reactant undergoes both oxidation and reduction is known as a disproportionation reaction.

Key Concepts

Oxidation Reaction

An oxidation reaction is a type of chemical reaction where a substance loses electrons, leading to an increase in its oxidation state. In the provided example, the substance of interest is chlorine in its chlorate ion, \(\mathrm{ClO}^{-}\). When analyzing the reaction \(3 \mathrm{ClO}^{-}(\mathrm{aq}) \longrightarrow \mathrm{ClO}_{3}^{-}(\mathrm{aq})+2 \mathrm{Cl}^{-}(\mathrm{aq})\), we see that one of the chlorine atoms undergoes oxidation. This occurs when its oxidation state increases from +1 in \(\mathrm{ClO}^{-}\) to +5 in \(\mathrm{ClO}_{3}^{-}\). The process of oxidation is accompanied by the loss of electrons, which is crucial for balancing reactions. Remember:

• Oxidation = loss of electrons
• Increase in oxidation state

Understanding the concept of oxidation is key in identifying disproportionation reactions as it encompasses both oxidation and reduction.

Reduction Reaction

A reduction reaction involves the gain of electrons by a molecule, atom, or ion. This gain results in a decrease in the oxidation state of the substance. In our reaction, one part of the chlorine in \(\mathrm{ClO}^{-}\) acts differently. While one chlorine atom is oxidizing, the other is reducing. Its oxidation state decreases from +1 in \(\mathrm{ClO}^{-}\) to -1 in \(\mathrm{Cl}^{-}\). This dual behavior demonstrates the classic features of a disproportionation reaction. Key points to identify reduction include:

• Reduction = gain of electrons
• Decrease in oxidation state

Knowing reduction helps to decipher both oxidation-reduction reactions and specifically, disproportionation reactions.

Oxidation States

The oxidation state, or oxidation number, is an indicator of the degree of oxidation of an atom in a chemical compound. It represents the hypothetical charge that an atom would have if all bonds to different atoms were completely ionic. When analyzing oxidation states in reactions:

• They help track the transfer of electrons
• If an atom's oxidation state increases, it has been oxidized
• If an atom's oxidation state decreases, it has been reduced

In the case of the reaction \(3 \mathrm{ClO}^{-}\rightarrow \mathrm{ClO}_{3}^{-} + 2 \mathrm{Cl}^{-}\), chlorine exhibits different oxidation states on the product side. On the reactant side, chlorine in \(\mathrm{ClO}^{-}\) is at oxidation state +1. In the products, it has +5 in \(\mathrm{ClO}_{3}^{-} \) and -1 in \(\mathrm{Cl}^{-} \). Establishing this helps in observing the flow of oxidation and reduction that constitutes a disproportionation reaction.

Chlorine Reactions

Chlorine is a versatile element that can exhibit a variety of oxidation states, ranging from -1 to +7. Its ability to undergo both oxidation and reduction in the same reaction is fascinating and is evident in disproportionation reactions, like the one with \(\mathrm{ClO}^{-}\). In the example, chlorine in \(\mathrm{ClO}^{-}\) is both oxidized to \(\mathrm{ClO}_{3}^{-}\) and reduced to \(\mathrm{Cl}^{-}\). This is a vivid illustration of chlorine's chemical behavior. Understanding chlorine reactions is key because:

• Chlorine's different oxidation states allow for multiple types of reactions.
• It helps in understanding how disproportionation works.
• It exemplifies the broader principles of oxidation and reduction in chemistry.

Chlorine's chemical behavior is a classic study case for learning about redox reactions and helps boost comprehensive understanding.