Q.(a) Define oxidation and reduction on the basis of electron transfer concept. Give example in each case.
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Start your 14-day free trial to unlock the full solution →Oxidation is electron loss and reduction is electron gain; in the first reaction H2S is oxidized and O2 is reduced, and in the second Sn is oxidized while the H of HCl is reduced.
(a) Definitions on the electron-transfer basis:
- Oxidation is defined as the loss of one or more electrons by an atom, ion, or molecule (which correspondingly increases its oxidation number). Example: Zn -> Zn2+ + 2e- (zinc loses 2 electrons to become Zn2+; oxidation number of Zn goes from 0 to +2).
- Reduction is defined as the gain of one or more electrons by an atom, ion, or molecule (which correspondingly decreases its oxidation number). Example: Cu2+ + 2e- -> Cu (Cu2+ gains 2 electrons to become neutral Cu; oxidation number of Cu goes from +2 to 0).
(b) Identifying oxidation and reduction in the given reactions:
Reaction 1: 2H2S + O2 -> 2S + 2H2O
In H2S, sulfur has oxidation number -2 (since H is +1 x 2 = +2, and the molecule is neutral, S = -2). In the product S (elemental sulfur), the oxidation number is 0. So sulfur's oxidation number rises from -2 to 0 -- it has lost electrons, so H2S is oxidized (sulfur is the species oxidized).
In O2, oxygen has oxidation number 0 (elemental). In the product H2O, oxygen has oxidation number -2. So oxygen's oxidation number falls from 0 to -2 -- it has gained electrons, so O2 is reduced (oxygen is the species reduced).
Reaction 2: Sn + 2HCl -> SnCl2 + H2 …
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