Rusting

• Rust is a chemical reaction between iron, water and oxygen to form the compound hydrated iron(III) oxide (rust)

  • Oxygen and water must be present for rust to occur
• During rusting, iron is oxidised

  • iron +  water + oxygen  →  hydrated iron(III) oxide
• To investigate the conditions required for rusting, prepare three test tubes as shown in the diagram

  • The oil in the 2nd tube keeps out air and the water has been boiled so that no air is left in it
  • The calcium chloride in the 3rd tube is used to remove any moisture in the air
  • After a few days, the iron nail in the 1st tube will be the only nail to show signs of rust
• Diagram showing the requirements of oxygen and water for rust to occur: only the nail on the left rusts

  A) air

  B) water

  C) boiled

  D) oil

  E) water

  F) air

  G) calcium chloride

  H) air

  I) water

  
• Barrier methods

  • Rust can be prevented by coating iron with barriers that prevent the iron from coming into contact with water and oxygen
  • However, if the coatings are washed away or scratched, the iron is once again exposed to water and oxygen and will rust
• Barrier methods

  A) grease

  B) oil

  C) paint

  D) plastic

  
• Only iron or steel (an alloy made from iron) can rust. If any other metal oxidises in air causing the metal to break down, you should say that the metal has corroded
• Rust is an orange-red colour and the reaction that takes place is called corrosion
• Conditions for rusting

  • Oxygen
  • Water
  • Can also be encouraged by salt
• Barrier methods:

  • painting e.g. ships, vehicles, bridges
  • oiling or greasing moving parts e.g. moving machinery
  • coating with plastic
  • plating e.g. cans, car bumpers