1. What is the chemical function of magnesium when it is connected to an iron pipe with a conducting wire?

Question

1. What is the chemical function of magnesium when it is connected to an iron pipe with a conducting wire?

Answer 1

Oxidation (rusting) is an electrochemical reaction.  Rusting of iron or steel pipes and tanks can be inhibited by connecting the iron-bearing thing to another metal that will accept the electron more readily than the iron.  This makes the other metal undergo the corrosion rather than the pipe or the tank.  Common sacrificial metals used to prevent rusting of steel and iron piping and tanks are zinc, aluminum, and magnesium.

iron goes to iron 2+ (which can then combine with hydroxide to make rust), giving off two electrons.  This means that the surrounding material (usually containing water) is grabbing two electrons.  The surrounding material doesn't care where the electrons come from, it just wants them.  So another metal that we don't care about what happens to it is provided instead, so that the electrons are grabbed from it instead of from the iron.  Instead of iron going to iron +2, you get zinc going to zinc +2 or magnesium going to magnesium +2.  This lets the tanks and piping last a lot longer without a lot of rusting.

EDIT small oops, I should have said "give up" rather than "accept" the electrons in the first paragraph.  Brain cramp, sorry.