Chemistry Revision Notes of Oxidation, Reduction and Electrochemistry for NDA Part-1
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Oxidation

The process of addition of oxygen or any other electronegative element or removal of hydrogen or any other electropositive element (or radical) by a substance, is known as oxidation.

e.g. `C+O_2 → CO_2`

`SnCl_2+Cl_2 → SnCl_4`

`H_2S + Cl_2 → 2HCl+S`

`2KI+H_2O → 2KOH+I_2`

The loss of one or more electrons by an atom, ion or molecule, is known as oxidation.

e. g `Na → Na^+ + e^-`

`Fe^(2+) → Fe^(3+) + e^-`

`2I^(-) → I_2+2e^(-)`

Increase in valency or oxidation number of an element is oxidation e. g. `FeCl_2 → FeCl_3` (valency of Fe changes from +2 to +3)

`overset(0)Zn+overset(+2)CuSO_4 → overset(+2)ZnSO_4 + overset(0)Cu`

`overset(0)Zn oversettext(Oxidation) → overset(+2)ZnSO_4+ overset(0)Cu` (oxidation number of Zn changes from zero to +2)

Oxidising Agents

`=>` The substance which undergoes reduction in a chemical reaction is known as oxidising agent or oxidant. Thus, oxidant is an electron acceptor.

`Zn+overset(42)CuSO_4 → ZnSO_4 +overset(0)Cu↓`

`overset(42)CuSO_4 oversettext(Reduction)→ overset(0)Cu↓`

As in above reaction, `CuSO_4` undergoes reduction, therefore, `CuSO_4 (Cu^(2+))` is an oxidising agent.

`=>` `F_2` is the strongest Oxidising agent.

`=>` Some oxides like `MgO , CuO , CO_2` and `CrO_3` are oxidants.

`=>` Some molecules are made up of electronegative elements, e.g `O_2 , O_3 , Cl_2 , Br_2 , I_2 , H_2O` etc. acts as oxidants.

`=>` The compounds in which elements are present in its highest oxidation number are oxidising agent, e.g. `HNO_3, KMnO_4, K_2Cr_2O_7, Na_2Cr_2O_7, H_2SO_4, FeCl_3, CuCl_2` etc.

`=>` All the positively charged species behaves as oxidising agents.

`=>` Oxidising agents are Lewis acids.

Reduction

The process of addition of hydrogen or any other electropositive element (or radical) or removal of oxygen or any other electronegative element (or radical) by a substance, is known as reduction, e.g.

`H_2S +Cl_2 → 2HCl +S` (reduction of `Cl_2`)

`2FeCl_3+Fe → 3FeCl_2` (reduction of `FeCl_3`)

`CuO+H_2 → Cu+H_2O` (reduction of `CuO` )

`FeCl_3+H_2S → FeCl_2+S` (reduction of `FeCl_3`)

`=>` The process of gain of one or more electrons by an atom, ion or molecule is known as reduction, e.g.

`Hg^(2+) + e^(-) → Hg^(+)`

`I_2+2e^(-) →2I^(-)`

`Cl+e^(-) → Cl^(-)`

`=>` Decrease in valency or oxidation number of an element is reduction, e.g. `Zn+overset(+2)CuSO_4 → ZnSO_4+overset(0)Cu ↓`

`overset(+2)CuSO_4 oversettext(Reduction) → overset(0)Cu↓`

Reducing Agents

`=>` The substance which undergoes oxidation in a chemical reaction is known as reducing agent or reductant. Thus, reductant is an electron loser. e.g. in the above example Zn is reducing agent.
`=>` All metals like `Zn, Na, Fe, AI, Mg, K` and few non-metals `C, S` etc., are reductants.
`=>` Hydracids of electronegative elements e.g. `HCl, HBr, HI, H_2S` etc., are reductants.
`=>` Compounds containing element in its lower oxidation state are also reductant, e.g. `Cu_2Cl_2, Hg_2Cl_2, SnCl_2, FeCl_2, CO, Cu_2O, Na_2S_2 O_3, KI` etc.
`=>` All negatively charged species behave like reducing agents.
`=>` Reducing agents are Lewis bases.

Note : White phosphorus has the property of only slow oxidation in air.

 
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