Cheat Engine

[GG]

The basic chemical formula for rust is Fe2O3 right? Yes. So why do you need water to cause rust? There is no Hydrogen in the end result. Where does the Hydrogen go? Does it fall off and bond to something else?

Also why do hot water systems have magnesium running through the centre? How does this stop rust?

Thanks, good answer = +rep (for rep whores)

[Cheat Engine User]

[DanielG]

Part 1 of your question:

When a droplet of water containing a little dissolved oxygen falls on an iron pipe, the iron under the droplet oxidizes:

Fe(s) «» Fe2+(aq) + 2 e-
The electrons are quickly snatched up by hydrogen ions and oxygen at the edge of the droplet to produce water:

4e- + 4 H+(aq) + O2(aq) «» 2 H2O(l)
More acidic water is expected to increase corrosion so long as there is a sufficient supply of oxygen. If the pH is very low, and there isn't enough oxygen, the hydrogen ions will snatch up the electrons anyway, making hydrogen gas instead of water:

2 H+(aq) + 2 e- «» H2(g)

But where's the rust? The equations above tell only a small part of the story.

Hydrogen ions are being consumed by the process. As the iron corrodes, the pH in the droplet rises. Hydroxide ions (OH-) appear in water as the hydrogen ion concentration falls. They react with the iron(II) ions to produce insoluble iron(II) hydroxides:

Fe2+(aq) + 2 OH-(aq) «» Fe(OH)2(s)
The iron(II) ions also react with hydrogen ions and oxygen to produce iron(III) ions.

Fe2+(aq) + 4 H+(aq) + O2(aq) «» 4 Fe3+(aq) + 2 H2O(l)
The iron(III) ions react with hydroxide ions to produce hydrated iron(III) oxides (also known as iron(III) hydroxides).

Fe3+(aq) + 3 OH-(aq) «» Fe(OH)3(s)
These can dry to make plain iron(III) oxide, Fe2O3. This is the red, powdery stuff we call "rust".

Since these processes involve hydrogen ions or hydroxide ions, they will be affected by changes in pH.


Part 2 of your question:

If you have other ions like calcium, carbonate or magnesium present, they make a variety of precipitates that mix in with the iron hydroxide precipitates to produce a crusty, gnarled coating which can slow corrosion under some circumstances by cutting the iron off from the acid, water, and air supply.

[Arcobaleno]

Its cos of the oxygen dissolved in the water (Reason fish can breathe underwater). You don't need water to rust, it just increases the rate of it.

[GG]

Thanks for the answers. My teacher said that H2O was like a road for the electrons to transfer...