The formal potential of $Fe ^{3+} / Fe ^{2+}$ in a sulphuric acid and phosphoric acid mixture $\left(E^{\circ}=+0.61 \,V \right)$ is much lower than the standard potential $\left(E^{\circ}=+0.77 \,V \right) .$ This is due to
Since, $H _{2} SO _{4}$ and $H _{3} PO _{4}$ both are strong acids so their presence makes the medium more acidic. The $Fe ^{3+}$ ions form complex, $\left[ FeHPO _{4}\right]^{+}$with these acid and hence, the concentration of $Fe ^{3+}$ ion reduces which results in lowering in the formal reduction potential.
An electrochemical cell is a device that is used to create electrical energy through the chemical reactions which are involved in it. The electrical energy supplied to electrochemical cells is used to smooth the chemical reactions. In the electrochemical cell, the involved devices have the ability to convert the chemical energy to electrical energy or vice-versa.
Classification of Electrochemical Cell:
Cathode
Denoted by a positive sign since electrons are consumed here
A reduction reaction occurs in the cathode of an electrochemical cell
Electrons move into the cathode
Anode
Denoted by a negative sign since electrons are liberated here
An oxidation reaction occurs here
Electrons move out of the anode
Types of Electrochemical Cells:
Galvanic cells (also known as Voltaic cells)
Chemical energy is transformed into electrical energy.
The redox reactions are spontaneous in nature.
The anode is negatively charged and the cathode is positively charged.
The electrons originate from the species that undergo oxidation.
Electrolytic cells
Electrical energy is transformed into chemical energy.
The redox reactions are non-spontaneous.
These cells are positively charged anode and negatively charged cathode.
