C15.1 Rusting
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How is corrosion caused?
By the chemical reactions between the metal and substances in the environment
What is rusting?
The corrosion of iron
How does rusting work?
Rust forms on the surface of iron and most steels This rust is a soft crumbly substance - it soon flakes off - exposing fresh iron so that more iron cna rust
What is the purpose of anhydrous calcium chloride?
To absorb water
What is the equation for the rusting of iron?
Iron + oxygen + Water = Hydrated Iron(III) oxide
How can you prevent rustng?
Coating the iron or steel with paint - oil or grease - plasitc
What is electroplating?
Metal coating can be applied to iron or steel by dipping the object in molten metal or by electroplating
What is galvanising?
The process of applying a protective zinc coating to steel or iron
Why is zinc good at coating?
Zinc is more reactive then iron Zinc is a stronger reducing agent then iron - stronger tendency to form positive ions As zinc atoms lose electrons they become oxidised Therefore any oxygen or water reacts with zinc rather than iron
What is sacrificial protection?
When a more reactive metal is sacrificed to protect the iron
What are some alternatives for zinc to protect iron?
Magnesium or aluminium
When is sacrificial protection used?
Used under harsh conditions such as when the iron is in contact with seawater Used where the coating is likely to be scratched such as when emptying commercial wheeli bins
What is the chemical name for rust?
iron oxide