Question

For $Zn$ acts as sacrificial or Cathodic protection to prevent rusting of iron because:
A. $E_{OP}^ -$ of $Zn < \;\;E_{OP}^ -$ of $Fe$
B. $E_{OP}^ -$ of $Zn > \;\;E_{OP}^ -$ of $Fe$
C. $E_{OP}^ -$ of $Zn = E_{OP}^ -$ of $Fe$
D. $Zn$ is cheaper than iron

Answer 1

In electrochemistry, electrode potential is the electromotive force of a galvanic cell built from a standard reference electrode and another electrode to be characterized. By convention, the reference electrode is the standard hydrogen electrode (SHE). It is defined to have a potential of zero volts.

Complete step by step answer:
In an electrochemical series, zinc is placed above iron in the series down the group and from top to bottom, the value of reduction potential increases and from bottom to top, the value of oxidation potential decreases. This means that the oxidation of zinc into its corresponding bivalent ion in the electrolyte is possible rather than the conversion of iron into its corresponding ions in the electrolyte. This means that the oxidation potential of zinc is greater than the oxidation potential of iron and can be represented as follows:
${(E_{OP}^ - )_{Zn}} > {(E_{OP}^ - )_{Fe}}$
The conversion of $Zn \to Z{n^{2 + }}$ takes place instead of $Fe \to F{e^{2 + }}/F{e^{3 + }}$ . Due to this phenomenon, the rusting of iron is prevented and there is no formation of rust in the presence of air or moisture.
Thus, the correct option is B. $E_{OP}^ -$ of $Zn > \;\;E_{OP}^ -$ of $Fe$.

Note:
Rust is an iron oxide, a usually reddish brown oxide formed by the reaction of iron and oxygen in the presence of water or air moisture. Several forms of rust are distinguishable both visually and by spectroscopy, and form under different circumstances. Rust consists of hydrated iron(III) oxides $F{e_2}{O_3}\cdot{H_2}O$ and iron(III) oxide-hydroxide $\left( {FeO\left( {OH} \right),{\text{ }}Fe{{\left( {OH} \right)}_3}} \right)$ . It is typically associated with the corrosion of refined iron.