Question

A cell is set up as shown in the figure. It is observed that the EMF of the cell comes out to be 2.36V. Which of the given statements is not correct about the cell?
 

A. Reduction takes place at magnesium electrode and oxidation at SHE.
B. Oxidation takes place at magnesium electrode and reduction at SHE.
C. Standard electrode potential for $M{{g}^{2+}}|Mg$ will be -2.36 V.
D. Electrons flow from magnesium electrode to hydrogen electrode.

Answer 1

Hint: Oxidation and reduction can be explained on the basis of oxygen transfer or electron transfer. Oxidation generally refers to gaining of oxygen but loses electrons and reduction is opposite of oxidation in this oxygen loses while electrons are lost.

Complete Solution :
EMF represents electromotive forces which can be explained as the electric potential produced by an electrochemical cell or it can also be produced by changing the magnetic field.
- As we know that oxidation is done on anode and reduction is done on cathode in the given example oxidation and reduction reactions can be shown as:
$Oxidation\ \text{Mg}\to \text{M}{{\text{g}}^{\text{2+}}}\text{+2}{{\text{e}}^{\text{-}}}$
$\operatorname{Reduction}\ \text{2}{{\text{H}}^{\text{+}}}\text{+2}{{\text{e}}^{\text{-}}}\to {{\text{H}}_{\text{2}}}$

- So we can consider that ${{E}_{cell}}$ is positive as $Mg$ is more reactive than hydrogen. Hence the oxidation process takes place at $Mg$ electrode and reduction will take place on SHE.
So, the correct answer is “Option B”.

Note: In general a generator or a battery is used for the conversion of energy from one form to another. In these cases one terminal becomes positively charged while the other becomes negatively charged. Therefore we can say that electromotive force is a work done on a unit electric charge.