Question

mini project on corrosion

Answer 1

Project Report "Corrosion" : As soon as the metals are extracted from their ores, the reverse process begins, i.e. nature tries to convert them back into the form in which they occur. This is due to the attack of the gases present in the atmosphere on the surface of the metal converting it into compounds such as oxides, sulphides, carbonates sulphates etc.

Topic - Corrosion

Def. - The process of slowly eating away of the metal due to attack of the atmospheric gases on the surface of the metal resulting into the formation of compounds such as oxides, Sulphides carbonates and sulphates is called corrosion.

Mechanism or theory of Corrosion
The most common example of corrosion is the rusting of iron. Rust is hydrated ferric oxide, Fe2 O3 x H2O. Some other example include tarnishing of silver, development of green coating on copper and bronze etc.

Mechanism or Theory of Corrosion :The theory of corrosion can be explained by taking the example of rusting of iron. The theory is called electrochemical theory because it explains the formation of rust on the basis of the formation of electrochemical cells on the surface of metal.

The formation of rust on the basis of this theory may be explained in the following steps :

(i) The water vapours on the surface of the metal dissolve CO2 and O2 from the air. Thus the surface of the metal is covered with the solution of CO2 in water, that is carbonic acid (H2 CO3)

H2O + CO2 -------> H2 CO3

This acts as an electrolytic solution of the cell. The carbonic acid and water dissociate to small extent as follows :

                    H2CO3                         2H+ + CO23-   

                       H2O                           H+ + OH–

(ii) Iron in contact with the dissolved CO2 and O2 undergoes oxidation as follows :

Fe -----------------------> Fe2+ + 2e- (Eo = 0.44V)

Thus the sites where the above reaction take place act as anodes. As a result of the above reaction, iron is converted into ferrous (Fe2+) ions.

(iii) The electrons lost by iron are taken up by H+ ion present on the surface of the metal which were produced by the dissociation of H2CO3 and H2O. Thus H+ ions are converted into H atoms.

H+ + e- --------------> H                         ---- 4

These H atom either react with the dissolved oxygen or oxygen from the air to form water.

4H + O2 ---------> 2H2 O                            ..5

Multiplying eqn. (4) with 4 and adding to eqn(5), the complete reduction reaction may be written as