(i) Suggest a scheme of classification of the following redox reaction

1.	(i) Suggest a scheme of classification of the following redox reactions:(a) N2(g) + O2(g) → 2NO(g)(b) 2Pb(NO3)2(s) → 2PbO(s) + 2 NO2(g) + \(\frac{1}{2}\)O2(g)(c) NaH(s) + H2O(I) → NaOH(aq) + H2(g)(d) 2NO2(g) + 2OH– (aq) → NO2– (aq) + NO3– (aq) + H2O(I)(ii) Why do the following reactions proceed differently?Pb3O4 + 8HCI → 3PbCI2 + CI2 + 4H2OAndPb3O4 + 4HNO3 → 2Pb(NO3)2 + PbO2 + 2H2O
Answer» (i) (a) In this reaction, nitric oxide is formed by combination of the elemental substances, nitrogen and oxygen. So, it is an example of combination redox reaction. (b) It involves breaking down of lead nitrate into three components. So, it is an example of decomposition redox reaction. (c) In this reaction, hydrogen of water has been displaced by hydride ion into dihydrogen gas. So, it is an example of displacement redox reaction. (d) This reaction involves disproportionation of NO₂ (+4 state) in to NO₂^– (+3 state) and NO₃^–(+5 state). So, it is an example of disproportionation redox reaction. (ii) Pb₃O₄ is actually a stoichiometric mixture of 2 mol of PbO and 1 mole of PbO₂. In PbO₂, lead is present in +4 oxidation state, whereas the stable oxidation state of lead in PbO is +2. PbO₂ thus can act as an oxidant and so, it can oxidise Cl^- ion of HCl into chlorine. As we know that PbO is a basic oxide. So, the reaction. Pb₃O₄ + 8HCI → 3PbCI₂ + CI₂ + 4H₂O can be splitted into two reactions- 2PbO + 4HCI → 2PbCI₂ + 2H₂O (Acid-base reaction) \(\overset{+4}{Pb}O_2+4H\overset{-1}Cl\rightarrow\overset{+2}{Pb}Cl_2+\overset{o}{Cl_2}+2H_2O\) (Redox Reaction) Since, HNO₃ itself is an oxidizing agent, so, it is unlikely that the reaction may occur between PbO₂ and HNO₃. However, the acid-base reaction occurs between PbO and HNO₃ as : 2PbO + 4HNO₃ → 2Pb(NO₃)₂ + 2H₂O + 2H₂O It is the passive nature of PbO₂ against HNO₃, that makes the reaction different from the one that follows with HCl.

(i) Suggest a scheme of classification of the following redox reactions:(a) N2(g) + O2(g) → 2NO(g)(b) 2Pb(NO3)2(s) → 2PbO(s) + 2 NO2(g) + \(\frac{1}{2}\)O2(g)(c) NaH(s) + H2O(I) → NaOH(aq) + H2(g)(d) 2NO2(g) + 2OH– (aq) → NO2– (aq) + NO3– (aq) + H2O(I)(ii) Why do the following reactions proceed differently?Pb3O4 + 8HCI → 3PbCI2 + CI2 + 4H2OAndPb3O4 + 4HNO3 → 2Pb(NO3)2 + PbO2 + 2H2O

Answer»

(i) (a) In this reaction, nitric oxide is formed by combination of the elemental substances, nitrogen and oxygen. So, it is an example of combination redox reaction.

(b) It involves breaking down of lead nitrate into three components. So, it is an example of decomposition redox reaction.

(c) In this reaction, hydrogen of water has been displaced by hydride ion into dihydrogen gas. So, it is an example of displacement redox reaction.

(d) This reaction involves disproportionation of NO₂ (+4 state) in to NO₂^– (+3 state) and NO₃^–(+5 state). So, it is an example of disproportionation redox reaction.

(ii) Pb₃O₄ is actually a stoichiometric mixture of 2 mol of PbO and 1 mole of PbO₂. In PbO₂, lead is present in +4 oxidation state, whereas the stable oxidation state of lead in PbO is +2. PbO₂ thus can act as an oxidant and so, it can oxidise Cl^- ion of HCl into chlorine. As we know that PbO is a basic oxide. So, the reaction.

Pb₃O₄ + 8HCI → 3PbCI₂ + CI₂ + 4H₂O can be splitted into two reactions-

2PbO + 4HCI → 2PbCI₂ + 2H₂O (Acid-base reaction)

\(\overset{+4}{Pb}O_2+4H\overset{-1}Cl\rightarrow\overset{+2}{Pb}Cl_2+\overset{o}{Cl_2}+2H_2O\) (Redox Reaction)

Since, HNO₃ itself is an oxidizing agent, so, it is unlikely that the reaction may occur between PbO₂ and HNO₃.

However, the acid-base reaction occurs between PbO and HNO₃ as :

2PbO + 4HNO₃ → 2Pb(NO₃)₂ + 2H₂O + 2H₂O

It is the passive nature of PbO₂ against HNO₃, that makes the reaction different from the one that follows with HCl.

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