Q21.31 P - Chemistry: Molecular Nature Of Matter And Change

Question

A voltaic cell is constructed with an  ${\text{Fe/Fe}}^{\text{2 + }}$ half-cell and an  ${\text{Mn/Mn}}^{\text{2 + }}$ half-cell. The iron electrode is positive. 

(a) Write balanced half-reactions and the overall reaction. 

(b) Diagram the cell, labeling electrodes with their charges and showing the directions of electron flow in the circuit and of cation and anion flow in the salt bridge.

Step-by-Step Solution

Answer

a) Overall reaction ${\text{ = Mn + Fe}}^{\text{2 + }}\to {\text{Mn}}^{\text{2 + }}\text{ + Fe}$

b) 

Step 1: Given in the question:

 

1. ${\text{Fe/Fe}}^{\text{2 + }}$ Half cell
2.  ${\text{Mn/Mn}}^{\text{2 + }}$ Half cell
3. Positive iron electrode, i.e., cathode

Step 2: Determining the Half-reactions that are balanced and the overall reaction:

Anode:  $\text{Mn}\to {\text{M}}_{\text{n}}^{\text{2 + }}{\text{ + 2e}}^{\text{ - }}$

Cathode:  ${\text{Fe}}^{\text{2 + }}{\text{ + 2e}}^{\text{ - }}\to \text{Fe}$

Overall impression:  ${\text{Mn + Fe}}^{\text{2 + }}{\text{ + 2e}}^{\text{ - }}\to {\text{Mn}}^{\text{2 + }}{\text{ + 2e}}^{\text{ - }}\text{ + Fe}$

 ${\text{ = Mn + Fe}}^{\text{2 + }}\to {\text{Mn}}^{\text{2 + }}\text{ + Fe}$

Step 3: Diagrammatic representation of the cell with labeling