Question

The charge required for the reduction of 1 mol of \[Mn{O_4}^ - to{\text{ }}Mn{O_2}\]is:
A.1 F
B.3 F
C.5 F
D.6 F

Answer 1

Hint:1 F is the charge on 1 mole of electrons and in this provided reduction reaction, find out the number of moles of electrons required and which will ultimately give the answer after calculating.

Step by step explanation:
In the given question, charge required has to be calculated when there occurs a reduction reaction given in the question. Now F in the option means Faraday and this faraday has a law in electrochemistry which is called a Faraday law of electrolysis.
On the basis of faraday’s law, we calculate how much charge is required when a species is reduced.
One faraday of charge means the magnitude of charge of 1 mole of electrons and numerically saying 1 F = 96500 Coulombs. It is also a unit of electricity but used generally in electrochemistry.
Now we will see the reduction reaction that is occurring in the given question which is represented as follows: -
\[Mn{O_4}^ - + {\text{ }}4{H^ + } + {\text{ }}3{e^ - } \to {\text{ }}Mn{O_2} + {\text{ }}2{H_2}O\]
So, this is the reaction occurring in this and we will now calculate the oxidation state of Mn changing in this reduction reaction.
Oxidation state of Mn in \[Mn{O_4}^ - \Rightarrow {\text{ }}x{\text{ }}-{\text{ }}4\left( { - 2} \right){\text{ }} = {\text{ }} - 1,{\text{ }}so{\text{ }}x = {\text{ }} + 7\]
Oxidation state of Mn in \[Mn{O_2} \Rightarrow {\text{ }}x - 2\left( { - 2} \right){\text{ }} = {\text{ }}0,{\text{ }}so{\text{ }}x = {\text{ }} + 4\]
So, in this we see that 3 moles of electrons are needed to convert \[Mn{O_4}^ - to{\text{ }}Mn{O_2}\]and 1 mole of electron has charge equals to 1 F and therefore, 3 moles of electrons will have charge equals to 3 F
So, the correct option is B i.e. 3F

Note:There is faraday law as well which is as important as this concept and questions are asked from that concept as well and there are 2 faraday’s law in which one states that amount of substance deposited directly proportional to electricity passed and other law states that amount deposited will be directly proportional to their equivalent weights.