121.

Write the various steps for balancing a redox equation by oxidation number method.

During a redox reaction, the total increase in oxidation number must be equal to the total decrease in oxidation number. This is the basic principle for balancing the chemical equation by oxidation number method. The following are the steps involved:

1. Writing the skeleton redox reaction.

2. Assign oxidation numbers of atoms in each compound above the symbol of the element.

3. Identify the element or elements which undergo a change in oxidation number.

4. Calculate the increase or decrease in oxidation number per atom. Multiply this number of increase/ decrease of oxidation number with the number of atoms which are undergoing the change.

5. The species (atoms, ions or molecules) involved in change in O.N. are now multiplied by a suitable coefficient so that the total increase in O.N. becomes equal to the total increase in O.N. The determination of the increase in oxidation number and a decrease in oxidation number (step 4) itself gives the values of these coefficients.

6. Balance the equation with respect to all other atoms except hydrogen and oxygen.

7. Finally, balance hydrogen and oxygen.

8. For balancing oxygen atoms, add a water molecule for each oxygen atom on the side deficient in oxygen.

9. In acidic medium, for balancing hydrogen atoms, add H⁺ ions for each hydrogen atom on the side deficient in hydrogen atoms. Be sure that all participants and charges are balanced in the final equation.

10. In a basic medium, if hydrogen remains unbalanced , add water molecule for each hydrogen atom on the side deficient in hydroxyl atoms and add an equal number Of hydrogen ions on the opposite side.