Q1: Protection of ship hulls against sea water corrosion is done by coating with zinc because of the fact that zinc compared to iron is

ANS:C - oxidised preferentially.

Protection of ship hulls against sea water corrosion is done by coating with zinc primarily because zinc undergoes preferential oxidation compared to iron. Explanation:

1. Galvanic Corrosion:
   • When two dissimilar metals are in contact in the presence of an electrolyte (such as seawater), galvanic corrosion can occur.
   • In this electrochemical process, one metal acts as the anode (where oxidation occurs), and the other metal acts as the cathode (where reduction occurs).
2. Preferential Oxidation:
   • Zinc has a higher tendency to undergo oxidation (lose electrons) compared to iron.
   • In the presence of seawater, zinc sacrificially corrodes, releasing electrons (oxidation reaction), while the iron hull of the ship remains protected.
   • This sacrificial corrosion of zinc helps prevent or significantly reduce the corrosion of the iron hull, extending the lifespan of the ship.
3. Galvanic Protection:
   • Coating the iron hull of the ship with a layer of zinc sacrificial anodes ensures that the zinc corrodes preferentially, acting as a sacrificial cathode to protect the iron.
   • This method of corrosion protection is known as cathodic protection or galvanic protection.
4. Advantages of Zinc:
   • Zinc is commonly used for sacrificial anodes due to its high reactivity and low cost.
   • It is more easily oxidized than iron, making it an ideal sacrificial material for cathodic protection in marine environments.
   • Additionally, zinc sacrificial anodes are relatively lightweight and easy to install, making them practical for use in ship hull coatings.
5. Other Considerations:
   • While cost and weight are factors in material selection, the primary reason for using zinc sacrificial anodes in ship hull coatings is their ability to sacrificially protect the underlying iron hull from corrosion.

In summary, coating ship hulls with zinc sacrificial anodes protects against sea water corrosion by sacrificially corroding in preference to the iron hull, thereby extending the lifespan of the ship. This sacrificial protection mechanism exploits the preferential oxidation of zinc over iron in marine environments.