Oxidation and Reduction on the basis of electrons transfer

These are reactions where electrons are transferred from one species (atom, molecule or ion) to another. We can write 'half' equations to show only what happens to the species losing electrons or a different 'half' equation to show the species gaining electrons.

The whole equation is put together by making sure that the numbers of electrons are balanced in each half equation and adding them together (when the electrons will cancel out)

Oxidation is a chemical process in which there is a loss of electrons. The species, which gets oxidized becomes more positive or less negative, e.g.,

Na → Na⁺ + e^- (Na is oxidized to Na⁺ )
Fe²⁺ → Fe³⁺ + e^- (Fe²⁺ is oxidized to Fe³⁺)

Reduction is a chemical process in which there is a gain of electrons. The species, which gets reduced becomes more negative or less positive, e.g.,

Cl₂ + 2e^- → 2Cl^- (Cl₂ is reduced to Cl^-)
S + 2e^- → S₂^- (S is reduced to S₂^- )

The Oxidizing agent is the species which accepts electrons, e.g.,

Sn⁴⁺ + 2e^- → Sn²⁺ (Sn⁴⁺ is an oxidizing agent)
F₂ + 2e^- → 2F^- (F₂ is an oxidizing agent)

The Reducing agent is the substance which loses electrons, e.g.,

Hg+ → Hg2+ + e- (Hg+ is a reducing agent)
Fe²⁺ → Fe³⁺ + e^- (Fe²⁺ is a reducing agent)

Examples

2FeCl2 + Cl2 → 2FeCl3

The iron changes from 2+ to 3+ and is therefore oxidised (removal of electrons)

The chlorine gains an electron to go from 0 to -1 and is therefore reduced (addition of electrons)

Zn + CuSO4  → Cu + ZnSO4

The zinc changes from oxidation state 0 to +2 (removal of electrons) it is oxidised (animation)

The copper changes from 2+ to 0 and is oxidised and is therefore reduced (addition of electrons)

Cr2O72- + 3SO2 + 2H+ → 2Cr3+ + 3SO42- + H2O

The chromium changes from +6 to +3 and is therefore reduced (gain of electrons)

The sulphur changes from +4 to +6 and therefore loses electrons = oxidation (loss of electrons)

2KI + Br2   → 2KBr + I2

The iodide ions (oxidation number = -1) change to iodine (oxidation number = 0) : oxidation

Bromine (element, oxidation number = 0) changes to bromide ions (oxidation number = -1) : reduction

5Fe2+ + MnO4- + 8H+  → 5Fe3+ + Mn2+ + 4H2O

The iron changes from 2+ to 3+ and is oxidised (removal of electrons)

The manganese atom changes from +7 to +2 and is therefore reduced (addition of electrons)

More post describing redox reaction

The Effects of Oxidation Reactions : Many metals are chemically active elements and get easily affected by substances like moisture, air, acids, etc. Example-Iron articles that are shiny when new, but get coated with a reddish brown powder when left for some time. This process is commonly known as rusting of iron. Rusting eventually causes structural weakness and disintegration of the metal.

When a metal is attacked by substances around it, it is said to corrode and this process is called corrosion. Corrosion causes deterioration of essential properties in a material..............Read more

In our daily life we come across phenomena like fading of the colours of the clothes, burning of combustible substances like cooking gas, wood and coal, .................................... Read more  

science class 10 oxidation, reduction and redox chemical reaction

Chemistry x - OXIDATION AND REDUCTION : Oxidation: A chemical reaction which involves addition of oxygen or removal of hydrogen or loss of electron(s) is called as oxidation.
2Mg + O2 →2MgO (addition of oxygen)
H2S + Br2 → 2HBr + S (removal of hydrogen)