Exams › JEE Advanced › Chemistry

Which of the following are disproportionation reactions? (a) 2 Cu+ -> Cu^(2+) + Cu (b) 3 MnO4^(2-) + 4 H+ -> 2 MnO4^(-) + MnO2 + 2 H2O (c) 2 KMnO4 -> K2MnO4 + MnO2 + O2 (d) 2 MnO4^(-) + 3 Mn^(2+) + 2 H2O -> 5 MnO2 + 4 H+

1. a and b only
2. a, b, and c only
3. b, c, and d only
4. a and d only

Correct answer: a and b only

Solution

Disproportionation: same element/atom oxidized and reduced simultaneously. (a) Cu+ (+1) -> Cu²+ (+2, oxidized) + Cu (0, reduced). YES. (b) MnO4²- (Mn is +6) -> MnO4⁻ (Mn +7, oxidized) + MnO2 (Mn +4, reduced). YES. (c) 2KMnO4 -> K2MnO4 + MnO2 + O2: Mn goes from +7 in KMnO4 to +6 in K2MnO4 (reduced) and +4 in MnO2 (further reduced). Oxygen in O2 comes from decomposition but Mn only gets reduced - there is also oxidation component. Actually Mn+7 -> Mn+6 and Mn+4 are both reductions; the oxidation is of O²- to O2 (0). So disproportionation involves different elements (Mn reduced, O oxidized). This is NOT a disproportionation of Mn alone; it could be classified as disproportionation of the compound but Mn itself doesn't get oxidized. NOT disproportionation in strict sense. (d) MnO4⁻ (+7) + Mn²+ (+2) -> MnO2 (+4): this is comproportionation (two different oxidation states of Mn come together). NOT disproportionation. Answer: a and b.

Related JEE Advanced Chemistry questions

• When an excess of potassium iodide reacts with copper sulfate solution, followed by the addition of sodium thiosulfate, which statement about the reaction is false?
• In the given reaction sequence occurring in an aqueous medium, identify the species X, Y, and Z in the following steps: S2O3²− reacts with Ag+ to form X (a clear solution), which further reacts with Ag+ to produce Y (a white precipitate). Over time, Y transforms into Z (a black precipitate).
• Which pair of substances generates hydrogen gas upon reaction?
• In order to determine the amount of MnCl₂ in an aqueous solution, it was fully converted into KMnO₄ using the reaction: MnCl₂ + K₂S₂O₈ + H₂O → KMnO₄ + H₂SO₄ + HCl (unbalanced equation). A few drops of concentrated HCl were added, and the solution was gently heated. Then, 225 mg of oxalic acid was gradually introduced until the purple color of the permanganate ion vanished. Calculate the mass of MnCl₂ (in mg) originally present in the solution. (Atomic masses in g mol⁻¹: Mn = 55, Cl = 35.5)
• In acidic medium, FeSO4 is oxidised to Fe³+ by KMnO4. If 250 mL of a FeSO4 solution reacts completely with 32 mL of 5 M KMnO4, what is the molarity of the FeSO4 solution?
• H2O2 is oxidised by MnO4⁻ in acidic medium, producing O2 and Mn²+. How many grams of O2 are produced when 1.5*10⁻³ moles of MnO4⁻ react with 1.7 milligrams of H2O2?

⚔️ Practice JEE Advanced Chemistry free + battle 1v1 →