Question

It requires substantial energy to reduce metal ore to pure metal. The reverse process, corrosion, happens spontaneously. The rusting of iron, the tarnishing of silver, and the formation of patina on copper and brass are some common examples of corrosion.

Rusting is the greatest corrosion problem because it occurs rapidly and because so many objects are made of iron and steel. A great deal of the annual production of iron goes simply to replace that lost by rusting. Iron will not rust in dry air or in water that is completely free of air. Oxygen gas and water must be present for iron to rust. Describe chemistry and electrochemistry of corrosion of iron and copper. In each redox reaction, specify the element that is being oxidized, the element that is being reduced, and identify the oxidizing and the reducing agent. Why cars rust more rapidly near the beach or in cold climate where salt is used to de-ice the roads?

Answer 1

Rusting of iron is a electrochemical process where there will be an anode formation, one cathod formation and one electrolyte (moisture)

Anodic reaction :

Fe----> Fe²⁺ + 2e-

Cathodic reaction :

2H₂O + 2 e-   -----------> 4OH-

overall reaction : Fe²⁺ + 2 OH-   ------------> Fe(OH)₂ --------> Fe(OH)₃ ----------> Fe₂O₃. xH₂O

                                                                                                                       rust

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Corrosion of Copper

Anodic reaction :

Cu----> Cu²⁺ + 2e-

Cathodic reaction :

2H₂O + 2 e-   -----------> 4OH-

overall reaction : Cu²⁺ + 2 OH-   ------------> Cu(OH)₂

In both this type of corrosion, metal is oxidized and H₂O is reduced. Metal is reducing agent and H₂O is oxidising agent.

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During rusting of metal moisture present in the environment act as electrolyte. Near the see coast the amount of salt in the environment is more. salt increases the electrical conduction of the electrolyte. Thus corrosion process will be faster.