Rusting (2)

Mechanism of rusting (1)

The surface of the iron in the middle of the water droplet where the concentration of oxygen is low serves as the anode (negative terminal)

Mechanism of rusting (2)

Iron atom, Fe loses electrons and undergoes oxidation to form iron(II) ions, Fe2+

Mechanism of rusting (3)

Half equation of oxidation at the anode: Fe(s) → Fe2+(aq) + 2e−

Mechanism of rusting (4)

Electrons flow through the iron, Fe to the end of the water droplet where the concentration of oxygen is higher

Mechanism of rusting (5)

The iron, Fe surface at that part becomes the cathode (positive terminal), where reduction occurs

Mechanism of rusting (6)

Oxygen, O2 that dissolves in water accepts electrons and undergoes reduction to form hydroxide ion, OH−

Mechanism of rusting (7)

Half equation of reduction at the cathode: O2(g) + 2H2O(l) + 4e− → 4OH−(aq)

Mechanism of rusting (8)

The iron(II) ion, Fe2+ produced reacts with hydroxide ion, OH− to form iron(II) hydroxide, Fe(OH)2

Mechanism of rusting (9)

Fe2+ is green but rust is brown because Fe(OH)2 undergoes continuous oxidation with oxygen to form Fe2O3.xH2O (rust)

Properties of fron(III) oxide, Fe2O3 or rust (1)

Is brittle, permeable and does not stick strongly