A very important laboratory reagent X is prepared from the naturally occurring ore pyrolusite. When pyrolusite is fused with alkali in the presence of O2, a green compound Y is produced. Y is converted to X by electrolysis or by treatment with ozone. Let a = oxidation state of the central

Question

A very important laboratory reagent X is prepared from the naturally occurring ore pyrolusite. When pyrolusite is fused with alkali in the presence of O2, a green compound Y is produced. Y is converted to X by electrolysis or by treatment with ozone. Let a = oxidation state of the central metal in the oxo-anion of Y, and b = number of equivalent (equal) bonds in the oxo-anion of X. Find (a - b).

Accepted Answer

0. Pyrolusite = MnO2. Fusion: MnO2 + 2KOH + (1/2)O2 -> K2MnO4 (potassium manganate) + H2O. Y = MnO4²- (manganate ion, green color). Oxidation state of Mn in MnO4²-: x + 4(-2) = -2 => x = +6. So a = 6. X = MnO4⁻ (permanganate), produced by electrolytic oxidation or ozone. The permanganate ion MnO4⁻ has tetrahedral geometry; due to resonance, all four Mn-O bonds are equivalent. So b = 4. Therefore a - b = 6 - 4 = 2.

Solution

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