Question

Suggest a scheme of classification of the following redox reactions. 

(a) N₂(g) + O₂(g) →2N(Xg) 

(b) 2Pb(NO₃)₂(s) → 2PbO(s) + 2NO₂(g) + 1/2 O₂(g)

(c) NaH(s) + H2O(l)→ 4NaOH(aq) + H₂(g) 

(d) 2NO₂(g) + 20H^–(aq) → NO₂^–(aq) + NO₃^– (aq) + H₂O(l)

Answer 1

(a) In this reaction, the compound nitric oxide is formed by combination of elemental substances like nitrogen and oxygen. Since the oxidation number of nitrogen increases from 0 to +2 and of oxygen decreases from 0 to -2 therefore, it is a combination redox reaction.

(b)

In this reaction, lead nitrate decomposes to form three products, viz, lead oxide, nitrogen dioxide and oxygen. Since the oxidation number of nitrogen decrease from +5 in lead nitrate to +4 in NO₂ in O₂, therefore, it is a decomposition redox reaction.

(c)

In this reaction, hydrogen of water has been displaced by hydride ion to form dihydrogen gas. Therefore, it is a displacement reaction. Since in this reaction, the oxidation number of hydrogen increases from -1 in hydride ion to zero in dihydrogen gas and that of hydrogen decreases from +1 in water to zero in dihydrogen, therefore, it is a displacement redox reaction.

(d)

This is a disproportionation reaction since here the oxidation state of nitrogen decreases from +4 in NO₂ to +3 in NO₂^– ion, as well as increases from +4 in NO₂ to +5 in NO₃ ion.