How to find the oxidation number of elements in a compound?
Answers
To assign oxidation number you should know the rules
Rules:
Oxidation number of free element is always ZERO
Example: The oxidation number of atoms in O2, H2 and N2 = 0
The oxidation number of Hydrogen is +1
Exception: In Metal hydrides the oxidation state of hydrogen is -1
The Oxidation state of IA group elements = +1
The oxidation state of IIA group elements = +2
The oxidation number of IIIA group elements = +3
The oxidation state of Oxygen = -2
Exception: The Peroxides and super oxides the oxidation state is -1, -1/2 respectively
The oxidation state of VIIA group elements = -1
Exception: In inter halides the oxidation state will differs
In neutral compound the sum of oxidation numbers of all the atoms = 0
In polyatomic ions the sum of the oxidation number is equal to charge on the ion
Example: Hydroxide ion (OH-) the oxidation number = -1
Example:
Each atom in a molecule possesses its own oxidation state.
For example: Water
Formula is H2O
In the above molecule the oxidation state of hydrogen = +1
The Oxidation number of Oxygen is X
In neutral compound the sum of oxidation numbers of all the atoms = 0
(+1) * 2 + X =0
2 + X = 0
X =-2
Example – 2:
H2SO4
Find the oxidation number of Sulphur in Sulphuric acid.
H = +1
O=-2
S=?
(+1)* 2 + X+ 4(-2) = 0
2 + X -8 =0
2 + X = 8
X = 8-2
=+6