Mole Concept Redox Questions
Here’s an “ingelious” way to solve redox questions related to mole concept.
Let’s look at a typical JC A Level H2 Chemistry question:
50 cm3 of a 0.10 moldm-3 solution of a metallic salt was found to react exactly with 25.0 cm3 of a 0.10 moldm-3 aqueous sodium sulfite. In this reaction, the sulfite ion is oxidised as follows:
SO32- (aq) + H2O(l) 
Find the total number of electrons gain/lose for each metallic ion = 
Since sulfite was oxidised, the metallic ion gets reduced (by 1).
As the original oxidation number of the metal was +3, the new oxidation number is now +2.
As an analogy, consider there are 25 boys in the class.
Each boy will pass \$2 to the girls in the class for a total of \$50 dollars.
If there are 50 girls in the class, each girl will receive \$1.
Since each girl has \$2 from the start, they will now have \$3 each.
