Question

An iron object is plated with a coating of cobalt to protect against corrosion. Does the cobalt protect iron by cathodic protection? Explain.

Short answer

No, the cobalt coating does not provide cathodic protection to the iron object. This is because iron has a lower oxidation potential (\(E^0 = -0.44 V\)) than cobalt (\(E^0 = -0.28 V\)), meaning iron has a higher tendency to lose electrons and get oxidized when compared to cobalt. For effective cathodic protection, a metal with a lower oxidation potential than iron should be used as a sacrificial anode or coating.

Step-by-step solution

Understanding Cathodic Protection

Cathodic protection is a technique used to prevent the corrosion of a metal surface by making it the cathode of an electrochemical cell. In this process, the metal that needs protection is connected to a more easily oxidized metal, called the sacrificial anode. The sacrificial anode corrodes preferentially, protecting the cathode (the metal we want to protect) from corrosion.

Oxidation Potentials of Iron and Cobalt

To determine if cobalt can protect iron by cathodic protection, we need to compare their oxidation potentials. Oxidation potentials are the tendencies of elements to lose electrons and get oxidized. The lower the oxidation potential, the more easily an element can get oxidized. The standard oxidation potentials of iron (Fe) and cobalt (Co) are as follows: Iron (Fe): \(Fe \to Fe^{2+} + 2e^-\) ; \(E^0 = -0.44 V\) Cobalt (Co): \(Co \to Co^{2+} + 2e^-\) ; \(E^0 = -0.28 V\)

Comparing Oxidation Potentials

Comparing the oxidation potentials, we can see that iron has a lower oxidation potential (\(E^0 = -0.44 V\)) than cobalt (\(E^0 = -0.28 V\)). This means that iron has a higher tendency to lose electrons and get oxidized when compared to cobalt.

Conclusion

Since iron has a higher tendency to lose electrons and get oxidized, cobalt does not provide cathodic protection to the iron object when used as a coating. To effectively protect the iron object by cathodic protection, a metal with a lower oxidation potential than iron should be used as a sacrificial anode or coating.