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Disproportionation Reaction: Meaning, Examples & Exam Importance

Q: 10. Can you give an example of a disproportionation reaction involving manganese?

Yes, manganate(VI) ions (MnO42-) can undergo disproportionation in acidic solution to form permanganate(VII) ions (MnO4-) and manganese(IV) oxide (MnO2). This clearly illustrates the simultaneous oxidation and reduction of manganese within a single reactant species.

How to Identify a Disproportionation Reaction in Chemistry?

The topic of Disproportionation Reaction is important in physics and chemistry and helps us understand the redox behavior of various elements and compounds, especially in competitive exams and in the study of chemical reactions.

Understanding Disproportionation Reaction

Disproportionation reaction refers to a type of redox (oxidation-reduction) reaction where a single element or compound undergoes simultaneous oxidation and reduction, producing two different products with the same element in higher and lower oxidation states. This concept is essential for understanding auto-redox reactions, balancing redox equations, and exam numericals in topics like electrochemistry, redox chemistry, and environmental science.

Formula or Working Principle of Disproportionation Reaction

A disproportionation reaction can be represented as:

Aⁿ → A^n-1 + Aⁿ⁺¹

Here, the same species (Aⁿ) acts as both an oxidizing and reducing agent – some molecules get oxidized, others get reduced. The change in oxidation number is a key signature of this reaction.

Here’s a useful table to understand disproportionation reactions better:

Disproportionation Reaction Table

Concept	Description	Example
Disproportionation	One element in a single compound is both oxidized and reduced	2H₂O₂ → 2H₂O + O₂
Comproportionation	Two species of the same element in different oxidation states form a product with intermediate state	MnO₄^– + Mn²⁺ → 2MnO₂

Worked Example / Practical Experiment

Let’s solve a problem step by step:
1. Identify the species with the same element in one compound (e.g., Cl₂ in basic medium).

2. Write the reaction: Cl₂ + 2OH^– → Cl^– + ClO^– + H₂O

3. Assign oxidation states: Cl₂ (0), Cl^– (–1), ClO^– (+1)

4. See that Cl is both reduced (to –1) and oxidized (to +1).

Conclusion: This stepwise analysis helps identify a disproportionation reaction and balance the equation correctly.

Practice Questions

Define disproportionation reaction with an exam-relevant example.
What is the general formula for a disproportionation reaction?
Which property distinguishes disproportionation from other redox reactions?
Write the disproportionation reaction of hydrogen peroxide in acidic medium.

Common Mistakes to Avoid

Forgetting that one atom must be both reduced and oxidized in disproportionation reactions.
Mixing up disproportionation and comproportionation, especially while balancing redox reactions.
Not checking the oxidation states carefully for all products and reactants.

Real-World Applications

Disproportionation reactions are widely used in biology (respiratory pathways), industry (chlorine bleaching), and environmental chemistry (decomposition of pollutants). Vedantu helps you relate these reactions to real-world and competitive exam contexts for deeper understanding.

In this article, we explored disproportionation reaction — its meaning, formula, worked examples, and role in redox chemistry. Keep exploring important chemistry concepts with Vedantu to strengthen your fundamentals and exam confidence.

FAQs on Disproportionation Reaction: Meaning, Examples & Exam Importance

1. What is a disproportionation reaction?

A disproportionation reaction is a redox reaction where a single element in one oxidation state is simultaneously oxidized and reduced, forming two different products. It's a special type of redox reaction involving self-oxidation and self-reduction.

2. How do I identify a disproportionation reaction?

Identify a disproportionation reaction by looking for a single reactant species that undergoes both oxidation and reduction. Check the oxidation states: one part of the reactant increases in oxidation state (oxidation), and another part decreases (reduction). The products will show these different oxidation states.

3. What are some examples of disproportionation reactions?

Common examples include the decomposition of hydrogen peroxide (H₂O₂) into water (H₂O) and oxygen (O₂), and the reaction of chlorine (Cl₂) with sodium hydroxide (NaOH) to produce sodium chloride (NaCl), sodium hypochlorite (NaClO), and water (H₂O). These showcase the simultaneous oxidation and reduction within a single reactant.

4. What is the difference between disproportionation and other redox reactions?

Unlike regular redox reactions where two different species are involved in oxidation and reduction, disproportionation features only one reactant undergoing both processes. In comproportionation, two reactants with the same element in different oxidation states react to form a single product with an intermediate oxidation state—the opposite of disproportionation.

5. How are disproportionation reactions relevant to the JEE Main exam?

Disproportionation reactions frequently appear in JEE Main questions on redox reactions and balancing chemical equations. Understanding the concept is crucial for correctly predicting products and balancing equations involving this reaction type. Expect questions testing your ability to identify disproportionation and solve numerical problems based on this concept.

6. What are some common mistakes students make when dealing with disproportionation reactions?

Common mistakes include failing to correctly identify the oxidation states of the elements in the reactant and products, leading to incorrect balancing of the equation. Another is confusing disproportionation with other redox reaction types. Students should carefully analyze oxidation state changes to avoid such errors.

7. Explain the disproportionation reaction of hydrogen peroxide (H₂O₂).

In the disproportionation of hydrogen peroxide, the oxygen atom in H₂O₂ (oxidation state -1) is both oxidized to O₂ (oxidation state 0) and reduced to H₂O (oxidation state -2). This reaction often occurs in the presence of a catalyst like manganese dioxide.

8. How do I balance a disproportionation reaction equation?

Balancing a disproportionation equation involves the usual steps of redox balancing: 1) Assign oxidation states. 2) Identify the oxidized and reduced species. 3) Write half-reactions for oxidation and reduction. 4) Balance the half-reactions (atoms and charges). 5) Multiply the half-reactions to equalize electron transfer. 6) Combine the half-reactions and simplify.

9. What is the role of oxidation states in identifying disproportionation reactions?

Oxidation states are crucial. A reactant undergoing disproportionation must contain an element with an intermediate oxidation state. The changes in oxidation states during the reaction clearly indicate the simultaneous oxidation and reduction of this element within the single reactant. Monitoring the oxidation state changes is key to identifying disproportionation.

10. Can you give an example of a disproportionation reaction involving manganese?

Yes, manganate(VI) ions (MnO₄^2-) can undergo disproportionation in acidic solution to form permanganate(VII) ions (MnO₄^-) and manganese(IV) oxide (MnO₂). This clearly illustrates the simultaneous oxidation and reduction of manganese within a single reactant species.

11. What chapters in the NCERT textbook cover disproportionation reactions?

The specific chapter covering disproportionation reactions in the NCERT textbook varies slightly depending on the edition and class level (11th or 12th). However, you will typically find the relevant content within the chapters on redox reactions and chemical bonding. Look for sections discussing oxidation-reduction reactions and oxidation states.