Disproportionation Reactions
Redox Reactions
5
JEE Qs
8%
Hard
50
min
Master assigning oxidation states to quickly identify the element undergoing simultaneous oxidation and reduction, and always consider the medium to determine correct products.
✅ Key Points for JEE
- 1Disproportionation is a specific type of redox reaction where a single element in a single reactant simultaneously undergoes both oxidation and reduction, forming products in higher and lower oxidation states.
- 2To identify a disproportionation reaction, assign oxidation states to all elements in reactants and products. Look for an element present in an intermediate oxidation state in the reactant, which then appears in two different products with both a higher and a lower oxidation state.
- 3Common elements/compounds that exhibit disproportionation include halogens (Cl2, Br2, I2) in alkaline medium, hydrogen peroxide (H2O2), phosphorus (P4), sulfur (S8), and nitrous acid (HNO2).
- 4The tendency and products of disproportionation often depend on reaction conditions, particularly the pH (acidic, neutral, or basic medium) and temperature (e.g., cold vs. hot alkali for halogens).
- 5Elements in their highest or lowest possible oxidation states cannot undergo disproportionation, as they can only be reduced or oxidized, respectively.
⚠️ Common Mistakes
- ✕Confusing disproportionation with comproportionation (where an element from two different oxidation states forms a single intermediate oxidation state product) or other types of redox reactions.
- ✕Incorrectly assigning oxidation states, leading to misidentification of the element undergoing simultaneous oxidation and reduction.
- ✕Ignoring the crucial role of reaction conditions (like pH or temperature) which can significantly alter the products formed during disproportionation.
📝 Practice Questions
See allQ63.Given below are two statements: Statement I: In the oxalic acid vs KMnO4 (in the presence of dil H2SO4 ) titration the solution needs to be heated initially to 60∘C, but no heating is required in Ferrous ammonium sulphate (FAS) vs KMnO4 titration (in the presence of dil H2SO4 ) Statement II: In oxalic acid vs KMnO4 titration, the initial formation of MnSO4 takes place at high temperature, which then acts as catalyst for further reaction. In the case of FAS vs KMnO4 , heating oxidizes Fe2+ into Fe3+ by oxygen of air and error may be introduced in the experiment. In the light of the above statements, choose the correct answer from the options given below (1) Both Statement I and Statement II are false (2) Both Statement I and Statement II are true (3) Statement I is false but Statement II is true (4) Statement I is true but Statement II is false 2025 (28 Jan Shift 1) JEE Main Previous Year Paper
Q69.Given below are two statements : Statement (I): In partition chromatography, stationary phase is thin film of liquid present in the inert support. Statement (II) : In paper chromatography, the material of paper acts as a stationary phase. In the light of the above statements, choose the correct answer from the options given below : (1) Statement I is true but Statement II is false (2) Statement I is false but Statement II is true (3) Both Statement I and Statement II are false (4) Both Statement I and Statement II are true
Q57.The species which does not undergo disproportionation reaction is : (1) ClO−3 (2) ClO− (3) ClO−2 (4) ClO−4
Q53.Which of the following oxidation reactions are carried out by both K2Cr2O7 and KMnO4 in acidic medium? A. Γ−→I2 B. S 2−→S C. Fe2+ →Fe3+ D. Γ−→IO3− E. S2O32−→SO42− Choose the correct answer from the options given below: (1) C, D and E Only (2) B, C and D Only (3) A, D and E Only (4) A, B and C Only
Q54.Only 2 mL of KMnO4 solution of unknown molarity is required to reach the end point of a titration of 20 mL of oxalic acid (2M) in acidic medium. The molarity of KMnO4 solution should be M.
Q58.The difference in the 'spin-only' magnetic moment values of KMnO4 and the manganese product formed during titration of KMnO4 against oxalic acid in acidic medium is _______ BM. (nearest integer)
NCERT Chapters
- Class 11 Chemistry Ch 8: Redox Reactions