New iron articles are shiny, but iron left exposed develops reddish-brown rust. When a metal is attacked by moisture, acids or other substances around it, the metal is said to corrode and the process is called corrosion.

• Iron forms reddish-brown rust.
• Silver develops a black coating.
• Copper develops a green coating.

Corrosion damages car bodies, bridges, iron railings, ships and other metal objects. Rusting causes serious economic loss because damaged iron must be repaired or replaced. Paint limits the contact of iron with air and moisture, so it slows rusting.

Board extension: Copper corrosion and material choice

This extension prepares you for a current CBSE application pattern. It is not an additional NCERT section.

• Copper exposed to moist air slowly develops a green coating of basic copper carbonate.
• This coating stays attached and helps shield the copper below from further attack.
• Iron rust is loose and flaky. When it falls away, fresh iron is exposed and corrosion can continue.
• Copper is malleable, so it can be made into thin sheets and shaped for roofs, domes and similar structures.

For a material-choice answer, do not write only “copper corrodes less.” Name the coating, compare what the two coatings do, and connect the chosen material property to its use.

When fats and oils are oxidised, their smell and taste change. This spoilage is called rancidity.

Rancidity can be slowed by:

• adding antioxidants to food containing fats and oils;
• keeping food in airtight containers;
• flushing packets with nitrogen so oxygen cannot easily reach the food.

Recall Activity 1.1

Magnesium burns with a dazzling flame in oxygen and changes into white magnesium oxide. Magnesium gains oxygen, so it is being oxidised.