[abcdef]

why does a nail oxidizes faster in salt water than in common water?

[constant thinker]

It has to do with conductivity. The Na+ and Cl- ions make the water more conductive which speeds up rusting.

Try looking it up on http://wikipedia.org , they may have an article on rusting. It's to laggy for me to access and give you a link sorry.

[Donaldson Tan]

Rusting is an electrochemical process.

In water, the following reaction occurs:
Fe -> Fe²⁺ + 2e

The electrons then travel within the water medium to the surface of the water where there is oxygen. Oxygen then accepts these electrons by the following reaction:
O₂ + 2H₂O + 4e -> 4OH^-

The iron(II) ions undergo furthur oxidation with atmospheric oxygen to produce Fe³⁺.

Fe³⁺ combines with the hydroxide ions to produce rust.

The slowest step in the reaction mechanism is actually the reduction of oxygen. The rate of electron transport from the Iron metal to atmospheric oxygen can be increased if the the conductivity of the aqueous medium increases. Note that water has a high dielectric constant, so it favours the aqueous solvation of ions. Adding salt increases the conductivity of the solution, thus increase the rate of electron transport. This aids in quickening the rate determing step.

Hence, rust occurs faster in salt solution.

[abcdef]

great, thanks a lot!