Question

In the equation given below, the number of electrons lost by one molecule of $ Fe{S_2} $ are:
 $ Fe{S_2} + {O_2} \to Fe{O_3} + S{O_2} $
(A) $ 6 $
(B) $ 2 $
(C) $ 1 $
(D) $ 11 $

Answer 1

Hint :To solve this question we will first find the oxidation number of each element in each molecule. Oxidation number is the number assigned to the compound which represents the number of electrons lost or gained. Loss of electrons in a redox reaction simply means that the element is undergoing oxidation.

Complete Step By Step Answer:
First let us determine the oxidation state of each element.
+2 -2 0 +3 -2 +4 -2
 $ Fe{S_2} + {O_2} \to Fe{O_3} + S{O_2} $
 We only need to determine the oxidation undergoing by $ Fe $ and $ {S_2} $ so let us see how many electrons are being lost.
     +1
+2 -2 0 +3 -2 +4 -2
 $ Fe{S_2} + {O_2} \to Fe{O_3} + S{O_2} $
             +5
So here we see that one electron is being lost by $ Fe $ and five electrons are being lost by $ {S_2} $
There the number of electrons lost by one molecule of $ Fe{S_2} $ will be $ 5 + 1 = 6 $
Therefore $ 6 $ electrons are lost.
So, the correct answer will be Option A.

Additional Information:
In the oxidation number method we determine the oxidation number of all atoms present. After determining the oxidation number, we multiply the atoms that have changed by small whole numbers. By doing this we make the total loss of electrons equal to the total gain of electrons.

Note :
The oxidation number of an element in its free or uncombined state is always taken as zero that is why we took the oxidation state of $ {O_2} $ as zero. Always see that if oxygen will be present as a peroxide then its oxidation state will be taken as $ - 1 $ and when it will be bonded with fluorine, the oxidation number will be $ + 1 $ other than these three cases the oxidation state of oxygen is usually $ - 2 $