9.3 Corrosion of Metals

Define corrosion

destruction of metal occurring in nature

Rusting requires H__ & __, & the metal atom loses __ to form ions
> thus is __ (redox)

h2o, o2, e, oxidation

Define rusting

corrosion of iron metal

Steel is an alloy of iron. Can it rust?

yes

Conditions w/ Iron Nails
1. A__ + H₂O
> p__ conditions for rust

air, perfect

Conditions w/ Iron Nails
2. B__ H₂O + oil
> No __ as H₂O boiled (gas diminishes)
> Oil layer prevents O₂ from e__
= no rust

boiled, o2, entering

Conditions w/ Iron Nails
3. D__ air
> A__ c__ c__ removes H₂O(g) from air
= no rust

dry, anhydrous calcium chloride

Conditions w/ Iron Nails
4. S__ water
> soln acts as e__
> so iron loses e- more easily
= s__ rusting

salt, electrolyte, speeds

Preventing Rust
1. Protective coat
> p__, greasing, thin plastic coating, tin plating
DISADV: needs to be constantly r__

painting, renewed

Preventing Rust
2. Preventing oxidation via s__ protection (galvanising)
> coat iron/steel w/ more r__ metal e.g. Zn
> if scratched, the coat corrodes f__, preventing iron from losing e-
DISADV: Zn ions are p__, so can’t be used for f__ storage

sacrificial, reactive, faster, poisonous, food