Q. 205.0( 1 Vote )
Nitric acid is an oxidising agent and reacts with PbO but it does not react with PbO2. Explain why?
Actually Nitric oxide reacts with both PbO and PbO2
Pb has an EC as: [Xe] 4f14 5d10 6s2 6p2. The outermost orbital can give 4 electrons, so can exhibit multiple oxidation states. In PbO the Oxidation number is +2 and that in PbO2 is +4. As seen by the EC, Pb can only donate 4 outermost electrons to gain an oxidation state of +4. Oxidation by nitric acid of PbO takes place as:
Oxidation of PbO2 takes place as:
As seen by the reactions of PbO2 we require drastic conditions and excess of nitric acid in order for the reaction to occur spontaneously. Also if we consider whether HNO3 can oxidize PbO or not, under non – reactive conditions, can be discussed. As PbO has ON as +2, it can undergo oxidation by giving two electrons to nitric acid to attain Pb4+ state. As there are no more valence electrons in the outer most EC of Pb it won’t undergo oxidation further, thus nitric acid cannot oxidize PbO2. Also the ionization energy for Pb to give 4 electrons is high as compared to Sn which shows ON +4. Thus oxidation is not possible for a Pb4+ ionic state.
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