Document page
chemistry igcse acapprinted 86 · PDF 86
145 pagesrevision 46934
printed 86 · PDF 86
Page image rendered from the stored file at 110 dpi; it sharpens as you zoom. Outlines are placed from each region’s stored position on the page (612 × 792 pt).
readable
Source of this text: embedded text layer. The better of the embedded text and OCR is kept.
86
The carbon anodes (made of graphite ) need to be replaced after some time because the oxygen at
the anode reacts with the carbon in graphite , forming carbon dioxide .
7. Corrosion and Rusting
Corrosion: Gradual degradation of metals, primarily due to reactions with water, oxygen,
or acids.
Iron Corrosion (Rusting): Rusting specifically refers to the formation of iron oxide (rust)
on iron.
Conditions Needed for Rusting:
Both water and oxygen are essential for rust to form on iron.
Rusting Reaction: 4Fe + 3O2 + 6H2O → 2Fe2O3⋅6H2O
Rust Prevention Methods:
Barrier Methods: Painting, oiling, or plastic coating to prevent oxygen and water contact.
Galvanization: Coating iron with a layer of zinc; zinc reacts first due to its position in the
reactivity series.
Sacrificial Protection: Using a more reactive metal (e.g., magnesium) that corrodes in place
of iron.