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Oxidation Reduction Reactions Oxidation Reduction Reactions In any chemical reaction, some substances get oxidized while others get reduced. According to the old concept, a chemical reaction is the one in which there is the addition of oxygen or removal of hydrogen. For example, S + O2 → SO2 In the given reaction, oxygen is added to sulfur to form sulfur dioxide, hence sulfur gets oxidized to sulfur dioxide. Zn + 2HCl → ZnCl2 + H2 While in this reaction, hydrochloric acid gets oxidized to zinc chloride. "The addition of electronegative elements or removal of electropositive element is also termed as oxidation". According to modern concept of oxidation, a reaction in which any element or atom donates a number of electrons and gets converted to a cation is termed as oxidation reaction. Hence the oxidation number increases in oxidation reaction. Removal of electron can take place from,

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Redox Equations :- In any chemical reaction, a species donating electrons forms the cation and the same electron is accepted by another to form the corresponding anion. In other words, a substance gets oxidized only in the presence of an oxidizing substance which gets reduced at the same time. Hence oxidation and reduction reactions occur simultaneously. Such type of reaction is known as redox reaction and balanced chemical equation of redox reaction is called as redox equation. Reduction and oxidation reactions are complementary to each other. For example, Fe2+ + MnO4- + 8H+ → Fe3+ + Mn2+ + 4H2O In given redox reaction one oxidation and one reduction take place, Fe2+ → Fe3+ + e- (Oxidation half reaction) MnO4-+ 8H+ + 5e- → Mn2+ + 4H2O (Reduction half reaction) Here Fe2+ lose one electron and form Fe3+, hence it’s a reducing agent and gets oxidized. However MnO4- is an oxidizing agent and gets reduced to Mn2+. Some substances act as reducing agents as well as oxidizing agents depending upon the reaction conditions. For example, Hydrogen peroxide (H2O2) acts as oxidant as well as reductant. In the reaction of hydrogen peroxide with bromide ion, H2O2 acts as oxidant. 2Br- + H2O2 → 2OH- + Br2 While in the reaction of H2O2 with silver oxide, H2O2 acts as reductant. Ag2O + H2O2 → 2Ag + H2O + O2 In the same way, nitrous acid, sulfur dioxide also act as both oxidant and reductant

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Let us take a simple example and try writing the redox equations for it. There are two main steps in writing redox equations. They are: <<-- Oxidation half reaction

<<-- Reduction half reaction

Copper metal reacts with aqueous silver nitrate solution to form aqueous Cu (II) ions in solution and solid silver metal. Copper metal + Aqueous Silver (I) ions → aqueous Cu (II) ions + Silver metal The half reaction for the oxidation process is the loss of two electrons from the more electro positive, copper metal. That is, Cu (s) → Cu 2+ (aq) + 2eIn the corresponding reduction process, a silver ion gains a single electron to form silver metal. That is, Ag+ (aq) + e- → Ag (s) Now, let us try balancing redox reactions. All the electrons lost in the oxidation half reaction must be accounted for by the redox half reactions. So, in order to balance redox reactions, two silver ions must be accepting the two electrons lost by the Cu to form two atoms of Ag(s). So, the reduction equation becomes, 2 Ag+ (aq) + 2 e- → 2 Ag (s) We get this by multiplying the reduction half reaction by 2.

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Oxidation Reduction Reactions