proceed differently ? Pb O + 8HCl → 3PbCl + Cl + 4H O and Pb O + 4HNO → 2Pb(NO ) + PbO + 2H O Pb O is actually a stoichiometric mixture of mol of PbO and mol of PbO . In PbO , lead is present in + oxidation state, whereas the stable oxidation state of lead in PbO is + . PbO thus can act as an oxidant (oxidising agent) and, therefore, can oxidise Cl – ion of HCl into chlorine.
We may also keep in mind that PbO is a basic oxide. Therefore, the reaction Pb O + 8HCl → 3PbCl + Cl + 4H O can be splitted into two reactions namely: 2PbO + 4HCl → 2PbCl + 2H O (acid-base reaction) + – + PbO + 4HCl → PbCl + Cl +2H O (redox reaction) Since HNO itself is an oxidising agent therefore, it is unlikely that the reaction may occur between PbO and HNO . However, the acid-base reaction occurs between PbO and HNO as: 2PbO + 4HNO → 2Pb(NO ) + 2H O It is the passive nature of PbO against HNO that makes the reaction different from the one that follows with HCl. (a) Oxidation Number Method: In writing equations for oxidation-reduction reactions, just as for other reactions, the compositions and formulas must be known for the substances that react and for the products that are formed.
The oxidation number method is now best illustrated in the following steps: Step : Write the correct formula for each reactant and product. Step : Identify atoms which undergo change in oxidation number in the reaction by assigning the oxidation number to all elements in the reaction. Step : Calculate the increase or decrease in the oxidation number per atom and for the entire molecule/ion in which it occurs. If these are not