HOW TO WRITE THE OXIDATION NO. ACCORDING TO ITS RULES

Asked by Aishwarya Devadasan | 14th Nov, 2013, 01:45: PM

Expert Answer:

There are several rules for assigning the oxidation number to an element.

 

  • The oxidation number of an atom in the elemental state is zero.
    Example: Cl2 and Al both are 0
  • The oxidation number of a monatomic ion is equal to its charge.
    Example: In the compound NaCl, the sodium has an oxidation number of +1 and the chlorine is -1.
  • The algebraic sum of the oxidation numbers in the formula of a compound is zero.
    Example: the oxidation numbers in the NaCl above add up to 0
  • The oxidation number of hydrogen in a compound is +1, except when hydrogen forms compounds called hydrides with active metals, and then it is -1.
    Examples: H is +1 in H2O, but -1 in NaH (sodium hydride).
  • The oxidation number of oxygen in a compound is -2, except in peroxides when it is -1, and when combined with fluorine. Then it is +2.
    Example: In H2O the oxygen is -2, in H2O2 it is -1.
  • The algebraic sum of the oxidation numbers in the formula for a polyatomic ion is equal to the charge on that ion.
    Example: In the sulfate ion, SO42-, the oxidation numbers of the sulfur and the oxygens add up to 2-. The oxygens are -2 each, and the sulfur is +6.

Answered by Vaibhav Chavan | 18th Nov, 2013, 10:04: AM

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