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Balancing of Equations:

  1. Ion-electron method
  2. Oxidation number method
    [Concept involved that in any chemical reaction e cannot be produced so no. of e s in O.H. & R.H. should be same]

 Note : To predict the product of reaction remember:

  • Free halogen on reduction gives halide ion (F2 → F)
  • Alkali metals on oxidation give metallic ion with +1 oxidation state.
  • In alkaline medium KMnO4 is reduced to K2MnO4 but in strong alkaline or neutral medium it reduces of  Mn+4
  • In acid solution KMnO4 is reduced to Mn2+
  • H2O2 on reduction gives water and on oxidation gives oxygen.
  • Dichromate ion in acid solution is reduced to Cr3+.

Nature of Oxides Based on Oxidation Number:

Lowest oxidation state                      →        Basic                     (MnO)
Intermediate oxidation state         →        Amphoteric       (Mn3O4, MnO2)
Highest oxidation state                     →        Acidic                  (Mn2O7)

Rules For Assigning Oxidation Number:

  1. Oxidation number of free elements or atoms is zero.
  2. Oxidation number of allotropes is zero.
  3. Oxidation number of atoms in homo-nuclear molecules is zero.
  4. Oxidation number of mono-atomic ions is equal to the algebraic charge on them.
  5. Oxidation number of F in compounds is – 1
  6. Oxidation number of H in its compounds is +1, except in metal hydrides where it is-1
  7. Oxidation number of O is-2in its compound, but in and in peroxides it is 1 and -0.5 in KO2
  8. Oxidation number of alkali metals in their compounds + 1.
  9. Oxidation number of alkaline earth metals in their compounds is + 2.
  10. The sum of oxidation number of all the atoms in a molecule should be zero and in an ion equal to its charge.

Average Oxidation Number : Find Oxidation Number of Fe in Fe3O4.

Fe3O4 is FeO. Fe2O3
O.N. of Fe in FeO is + 2         ;           O.N. of Fe in Fe2O3 is + 3.

Therefore average O.N. of three Fe atoms (+2 + 2x (+3))/3 = +(8/3)

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