plz explain me oxidation no. method

Dear Student,

@ V. sidharth,

Right answer! Let us understand oxidation method with the help of an example. Potassium dichromate (VI) [i.e., K₂Cr₂O₇] reacts with sodium sulphite [i.e., Na₂SO₃] in an acid solution to produce chromium (III) ion and sulphate ion. 

Steps involved in this method:  

1. First write the skeletal ionic equation for the given reaction. 

2. Identify the oxidation number of all the elements.

3. Calculate the increase and decrease of oxidation number and make them equal.

4. Add H⁺ or OH⁻ ions to the expression on the appropriate side so that the total ionic charges of reactants and products are equal. In acidic medium, use H⁺ ions and in basic medium, use OH⁻ ion.

The given reaction occurs in the acidic medium and therefore, 8H⁺ are added on the left to make ionic charges equal.

5. Count the hydrogen atoms on the two sides and then add appropriate number of water molecules (i.e., 4H₂O) on the right to achieve balanced redox reaction.

Now the redox reaction is balanced.

The study material (Balancing of Redox Reaction) explaining balancing of redox reaction by oxidation method is available with animation on the site. You can refer to that.