Chemistry – Metals - Corrosion of metals | e-Consult

(a) Magnesium is used to protect the steel beam because magnesium is more reactive than iron. According to the reactivity series, magnesium is positioned above iron. This means magnesium has a greater tendency to lose electrons and is therefore more readily oxidized than iron. As a result, magnesium will corrode preferentially, protecting the iron from corrosion.

(b) When the magnesium strip is attached to the steel beam, it acts as the anode and the steel beam acts as the cathode. The magnesium atoms lose electrons to become magnesium ions (Mg²⁺), which dissolve into the solution. These electrons flow to the steel beam. This influx of electrons causes the iron atoms in the steel beam to gain electrons and remain in their metallic state, preventing them from oxidizing and corroding. The magnesium 'sacrifices' itself to protect the iron by providing a more readily oxidizable metal.