A piece of magnesium can be attached to the iron hull of a boat to prevent it from rusting. (a) Why is the magnesium called a sacrificial metal? (b) How does the Mg keep the iron hull from rusting? (c) Which can be thought of as the positive cathode, the \(\mathrm{Mg}\) or the steel hull? Explain. (d) Putting a block of \(\mathrm{Mg}\) on a steel boat hull does not create a battery. Why not?

(a) Magnesium is called a sacrificial metal because it preferentially oxidizes instead of the iron in the steel hull, due to its higher reactivity, thus protecting the iron from rusting. (b) Magnesium protects the iron hull from rusting by forming a galvanic cell, releasing electrons upon corrosion that are then absorbed by the iron, preventing oxidation and consequently rusting. (c) The steel hull can be thought of as the positive cathode, as it accepts electrons transferred from the corroding magnesium (the anode) in the galvanic cell setup. (d) A block of magnesium on a steel boat hull does not create a battery because the main purpose is corrosion protection, not storing electrical energy. There is no complete electrical circuit, and the electrochemical reaction is not reversible, which is required for batteries.