Chapter 20.2, Problem 18SSC

Interpretation Introduction

Interpretation:

Function of sacrificial anode and its functional similarity with galvanization is to be explained.

Concept introduction:

Corrosion is the slow process of degradation of metal due to attack of atmospheric gases on its surface. Attack by ambient atmosphere leads to the formation of oxides, sulfates, carbonates of metal. Rusting is a type of corrosion in which iron get converted to hydrated ferric oxide.

Factors that promote corrosion:

• Reactivity of the metal
• Presence of impurities in metal
• Presence of air and moisture
• Presence of electrolyte

Corrosion can be protected by various methods such as barrier protection, sacrificial protection and electrical protection.

Answer to Problem 18SSC

Active metal or more electropositive metal like magnesium, aluminum and titanium, which lose electron (oxidize) more readily in exposure with moist air in comparison to iron hence protect it from rusting are called sacrificial anode.

Sacrificial anodes are likened to galvanization as in the latter process too iron is coated with more electropositive zinc by electroplating or dipping iron in molten zinc, which get preferentially oxidized when moist air comes in contact of iron surface.

Explanation of Solution

To prevent corrosion, iron surface is covered by active metal or more electropositive metal like magnesium, aluminum and titanium, which lose electron(oxidize) more readily in exposure with moist air in comparison to iron hence protect it from rusting. They are referred as sacrificial anodes as they get corroded to protect iron from corrosion.

Function of magnesium as sacrificial anodes can be shown as follows:

At anode: $\text{Mg}\left(\text{s}\right)\to {\text{Mg}}^{2+}\left(\text{aq}\right)+2{\text{e}}^{-}$

At cathode: ${\text{O}}_2\left(\text{g}\right)+4{\text{H}}^{+}\left(\text{aq}\right)+4{\text{e}}^{-}\to 2{\text{H}}_2\text{O}\left(\text{l}\right)$

Sacrificial anodes are likened to galvanization as in the latter process, iron is coated with more electropositive zinc by electroplating or dipping iron in molten zinc.

Similar to sacrificial anode, zinc too get preferentially oxidized when moist air comes in contact of iron surface.

Conclusion

Active metal or more electropositive metal like magnesium, aluminum and titanium, which lose electron (oxidize) more readily in exposure with moist air in comparison to iron hence protect it from rusting are called sacrificial anode.

Sacrificial anodes are likened to galvanization as in the latter process too iron is coated with more electropositive zinc by electroplating or dipping iron in molten zinc, which get preferentially oxidized when moist air comes in contact of iron surface.